CHAPTER 34 Safety, Security, Comfort Systems, and ...

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INTRODUCTION Each year brings more advanced features to automo-biles. What was only found on expensive luxury vehi-cles a few short years ago is now commonplace on many cars. Safety, security, and navigation systems are covered in this chapter as well as other systems like sound systems, which are common features on today’s vehicles. Some comfort systems are added to a new vehicle in the aftermarket or at the dealer, while oth-ers are provided as original equipment by the manu-facturer. Figure 34.1 shows some typical safety and comfort enhancements on a modern car.

SUPPLEMENTAL RESTRAINT SYSTEMSIt is estimated that somewhere in the world, a person dies in an automobile accident every second. During a collision, the force of a 2-ton vehicle must come to a

active alarm systemactive restraintair bag moduleamplitude modulationcrossoverfrequency modulation

inertia wheelmultistage ABSoccupant sensor system (OSS)passive alarm systempassive restraintresistance key

safi ng sensorsshorting barsquibstransponder key

KEY TERMS

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OBJECTIVESUpon completion of this chapter, you should be able to:■ Explain how passive restraints work.■ Give examples of passive and active restraints.■ Describe air bag system operation.■ Demonstrate knowledge of the operation and service of security systems.■ Describe the operation of vehicle comfort systems and electrical accessories.■ Explain the operation of and differences among various vehicle sound systems.■ Troubleshoot problems with electrical accessories.

Safety, Security, Comfort Systems, and Electrical Accessories

stop very fast. The force on the vehicle is great because its momentum changes instantly, but the passenger’s momentum has not changed—yet. Seat belts and air bags are examples of supplemental restraint systems. They are designed to stop the passenger’s momentum with as little damage as possible. This is a huge objec-tive. The driver and passengers are located very close to the steering wheel and dash, and a fraction of a sec-ond is all that is available to accomplish the task. That small space in time is enough of a lifesaving opportu-nity to allow the system to slow the passenger, instead of allowing an instant halt to his or her motion.

Automobile manufacturers realize that safety rat-ings are very important to the public. Their vehicles are designed to be able to absorb the force of an acci-dent. Intensive crash tests are performed on vehicles from the front, side, and rear.

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Safety, Security, Comfort Systems, and Electrical Accessories 503

One in four accidents is a side impact, in which the passengers are especially vulnerable. Side impact beams are installed during manufacturing. They are designed to minimize injury to the passenger from collisions from the side. Additionally, pillars are installed to protect the passengers in case of a rollover.

ACTIVE AND PASSIVE RESTRAINTSPassenger protection includes active and passive restraints:■ An active restraint is one that the passenger

must activate. An example of an active restraint is a manually buckled seat belt.

■ A passive restraint is something that takes place automatically to protect the occupant of a vehicle. Automatic seat belts or air bag systems are examples of passive restraints (Figure 34.2).

Seat BeltsThe fi rst seat belt in an American car was installed on a 1956 Ford. By 1964, seat belts were available as standard equipment. In 1967, they were mandatory equipment. Today seat belts and air bags are required on all cars and light trucks.

Energy absorbing steering column

Multistage front air bags with occupant classification system

Tire pressure monitoring

Antilockbrake system

Collisionavoidance

radar

Power adjustable pedals

Inflatableknee blockers

Three-pointshoulder belts

Seat beltpretensioners

LATCH child seat anchor system

Electronic stability program

Rear park assist system

Three-rowside curtain air bags

Adaptivehead lights

Figure 34.1 Modern vehicles have many safety and comfort enhancements.

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Figure 34.2 An example of passive restraint: an air bag system as seen from above.

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A seat belt is often a combination of a lap belt and a shoulder belt. This is called a three-point belt. The belt that goes across a person’s lap is called a lap belt. A shoulder belt is the part of the belt that extends across a person’s shoulders and chest. One end of the belt has a buckle, and the other end is attached to an anchor that attaches it to the fl oor or seat (Figure 34.3). The buckle must be able to withstand a 2-ton load without releasing.


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Five-point safety harnesses are used in children’s seats and in racing (Figure 34.4). The lap part of the belt is connected to a harness between the legs. Six-point har-nesses used in racing have two leg harnesses because this is the area most likely to fail in a high-speed collision.

Early seat belts were sometimes diffi cult to buckle and/or adjust. In 1968, Volvo introduced the seat belt inertia wheel. It allowed the belt to be more comfortable for the passengers and eliminated the need to adjust the belt for each passenger. Today’s modern vehicles have belt pretensioners or retractors (Figure 34.5). Late-model, smart seat belts control the slack in seat belts during a collision. These are cov-ered later in this chapter.

Front seat belt

Shoulder anchoradjuster

Rear seat belt Child seatanchor plate

Rear center belt andrear seat belt buckles

Front seatbelt buckles

Figure 34.3 Parts of a seat belt system.

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Figure 34.4 A fi ve-point harness used for racing has a center strap.

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Figure 34.5 A seat belt retractor.

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■■ HISTORY NOTE ■■

The three-point safety belt was invented by Nils Bohlin and patented by the Swedish auto maker Volvo in 1959. Volvo was a pioneer in the fi eld of automotive safety. By 1963, all Volvos came equipped with three-point belts. Three years later, in 1966, Volvo released a report called “the 28,000 accident report” showing that thousands of lives had been saved already by three-point belts. This report proved to be the basis for the 1977 legislation requiring the installation of passive seat belts in all cars sold in the United States by the 1984 model year.



Current seat belt use is estimated at only 70%.There are three different styles of pretensioners:

■ Mechanical pretensioners use an inertia wheel, a pendulum-like device that locks during sudden deceleration (Figure 34.6).

■ Electric pretensioners are activated by a sensor. They can be a part of the air bag circuitry.

■ Pyrotechnic tensioners work with air bags. They are also activated by a sensor. An explosive charge removes slack and locks the belt. They must be replaced once they have been used. These devices are covered later in this chapter.

Seat belt systems also include a sensor and a warn-ing system consisting of an instrument panel light as well as a bell or buzzer. With a passive system, the warn-ing light is illuminated for a few seconds. If the belt is not buckled, an audible warning sounds. The audible system can also sound when a door is open.

In a passive seat belt system, electric motors oper-ated by the ignition switch move shoulder belts across the driver and front seat passenger (Figure 34.7). The shoulder and lap belts are separate, so there are two retractors.

Air BagsAir bag systems are truly remarkable. As you read the following information, air bag systems are called air bags, supplemental infl atable restraints (SIR), supple-mental air restraints (SAR), or supplemental restraint systems (SRS). Driver-side air bags were installed on many cars beginning in 1995. Driver- and passenger-side air bags have been required on all new cars, light trucks, and vans sold in the United States since 1999. The National Highway Traffi c Safety Administration (NHTSA) estimates that front air bags reduce head-on fatalities by 29% when drivers are wearing seat belts and 34% when they are not. When the seat belt is com-bined with air bags, serious head and chest injuries are reduced by 65% to 75%.

An air bag is a fl exible nylon bag that infl ates almost instantaneously in the event of a serious

Figure 34.6 An inertia wheel locks during sudden deceleration.

Weight

Inertia wheel

Figure 34.7 A passive seat belt system.

Kneepanel

Belt guide

Emergency lockingretractor assembly

Outer beltassembly(manual lap belt)

Inner belt assembly(manual lap belt)

Motor

Rail andmotor assembly

Emergency releasebuckle

Shoulderbelt

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collision. The infl ating bag protects the passenger from a serious upper body or head injury. The air bag infl ates at about 200 mph. The entire infl ation and defl ation cycle occurs in less than one-half second. The average speed of all manufacturers’ air bag deploy-ment is 33 mS.

In the early air bag systems, the force of a collision suffi cient to deploy the air bag needed to be equivalent to that of a vehicle running into a wall at approxi-mately 14 miles per hour (mph). Hitting a solid wall at this speed is equivalent to a moving vehicle collid-ing with a stationary vehicle at about 28 mph. This threshold prevented accidental deployment due to hit-ting a curb or during a panic stop. With the car parked and the ignition off, deployment was unlikely because there was no power to the circuits to deploy the air bag. Newer systems have far more sophisticated deployment criteria; they are discussed later in the chapter.

Driver-side air bags are mounted in the steering wheel. The air bag is folded with talcum power or cornstarch in a cover that is designed to break open when the bag is deployed (Figure 34.8). The steering wheel cover in a car with an air bag usually is labeled (Figure 34.9) with SRS or SIR.

Early, simple air bag systems included remote mechanical impact sensors with an additional sensor in the control module to deploy a single driver-side air bag (Figure 34.10). Like today’s electronic systems, these systems used a pyrotechnic device for infl ation. Today’s systems, however, have become considerably more sophisticated and complicated.

The following are some of the additional types of air bags available:■ Passenger-side air bags■ Side air bags in seat backs■ Side curtain air bags above the headliner■ Knee air bags■ Rear seat air bagsThese are all used with seat belt pretensioners, which remove the slack from seat belts.

Passenger Air Bags. A passenger-side air bag is located in the top of the dashboard on the passenger side, contained under a small door (Figure 34.11). The windshield is an integral part of the passenger-side air bag system, and it must be correctly glued in place. In some passenger air bag systems, the air bag deploy-ment bounces off the windshield and is very violent. A passenger-side air bag deployment will often break the windshield. When an air bag inflates and the win-dows are all up, doors can be forced open and damage to the vehicle body can occur due to the increase in passenger compartment pressure.

Most often both front air bags are deployed together. It is rare that only one goes off. For that reason, an undeployed bag is usually replaced along with the one that deployed. From accident reports, it has been estimated that 1% to 2% of air bags do not deploy due to system failure.

Side Air Bags. The side area of the vehicle is very close to the driver. One-quarter of all injuries from

Figure 34.9 A driver-side air bag mounted in the center of the steering wheel.

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Igniter

Seals

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Figure 34.8 (top) Cutaway of a driver-side air bag and infl ator. (bottom) An igniter assembly is beneath the bag.

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automobile accidents are from side impacts. Yet these accidents account for over a third of the serious inju-ries and fatalities. At least half of the injuries resulting from side impacts are head injuries. The United States

Department of Transportation estimates that one-quarter of all automobile-related deaths could be pre-vented by side air bags designed to protect the head.

Side air bags have infl ator modules in either the front door or front seat (Figure 34.12) on either side of the vehicle. There is very little time to infl ate the bag in a side collision. The bag must infl ate in less than 10 mS. Side curtain air bags are discussed later.

Figure 34.10 An earlier, simpler air bag system.

Control module

Driver-sidedoor switch

Tunnel sensorand safing

sensor

Electricalwiring

Left impactsensor

Center impactsensor

Right impactsensor

Air bag module Clock spring

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Figure 34.11 A passenger-side air bag.

Windshield

Dash coverbreaks away here.

Air bag

Inflator

Hinge

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Figure 34.12 A side air bag in the seat.

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passenger wearing a seatbelt survives an accident dur-ing which an air bag deploys, leg injuries account for most of the injuries (Figure 34.15). Sixty percent of the leg injuries are below the knee.

The knee air bag reduces the risk of the person sliding free under the seat belt during an accident. It also keeps the person in a better position for front air bag protection.

Rear-Seat Air Bags. Rear-seat air bags are relatively uncommon. They are installed in the rear cushion of the front seats in some luxury automobiles to protect passengers in the rear in the event of a front impact.

Air Bag System PartsA modern air bag system has an electronic control unit (ECU). The air bag and its infl ator are called an air bag module. If there is a passenger-side air bag, there are two modules. The air bag system also includes sensors, an ignition device, an explosive propellant, and other parts.

The instrument panel has an air bag warning lamp that lights when the system detects a problem.

A clock spring makes the connection between the steering wheel and column (Figure 34.16).

A computer-controlled module monitors the sys-tem. It has an electrical storage capacitor that provides a safety backup in the event that the battery is dam-aged or disconnected during a collision.

More advanced air bag systems, called second-generation air bags, have a sensing diagnostic mod-ule (SDM) that controls multiple-stage front air bag deployment. Second-generation systems, which first appeared in 1994, include side air bags, electronic frontal sensors, and occupant detection and posi-tion sensors. The SDM has energy reserve in case the battery is disconnected, but unlike the first-generation system, the SDM completes the electrical

Figure 34.13 This seat belt tensioner has an explosive charge that pulls the belt tighter when the air bag is deployed.

Pyrotechnicdevice

Buckleretracts

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Figure 34.14 A knee air bag.

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Figure 34.15 Leg injuries account for a majority of injuries where an air bag is deployed.

Head/faceinjury

Leg injury50

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Seat Belt Pretensioners. Seat belt pretensioners are sometimes used in combination with an air bag. They are located on the seat belt buckles. A small explosive charge can take up to 6" of slack out of the lap and shoulder harnesses during a front collision (Figure 34.13). Pretensioners are usually deployed at the same time as the driver- and passenger-side air bags. The belt tensioner can only deploy if the seat belt is buckled.

When a seat belt tensioner deploys, the system has more time to infl ate the air bag. Today‘s systems infl ate the bag in stages, depending on the severity of the crash. More time allows for gentler infl ation, which results in fewer injuries caused by the air bag. Air bag deployment can result in injuries, but most are scrapes and abrasions. Serious injuries are rare.

Knee Protection Systems. The part of the dashboard designed to protect the knees of the driver and pas-senger is called a knee bolster. Some air bags are for the knees (Figure 34.14). General Motors’ Delphi Automotive calls theirs an active knee bolster. When a



The amount of physical damage to the vehicle is not what determines whether or not an air bag will be deployed. In fi rst-generation systems, there are usu-ally three or more crash sensors that work with the control module to determine the difference between a crash and a noncrash by measuring the severity of the impact. Sensors are located either on the outside or the inside of the vehicle, depending on their function. Front impact sensors, sometimes called discriminating sensors, are usually found in the engine compartment near the radiator.

Inside sensors are called safi ng, or arming, sensors. Their function is to determine whether there has actually been a crash. Safi ng sensors are most often located in the center console. They can also be located in different locations in the passenger compartment, depending on the manufacturer. Sometimes they are part of the control module.

During sudden deceleration, a sensor’s contacts close electrically and send a signal to the control mod-ule. Before any action can be taken, the module fi rst needs to receive a signal from the safi ng sensor, at the rear of the vehicle.

NOTE: At least two sensors must say there is a crash before an air bag will be deployed. The safing sensor is on the power side of the circuit. One of the front discriminating sensors must provide the ground to the squib or no deploy-ment will take place.

In fi rst-generation systems, most impact sensors operate when a suffi cient impact occurs within a 60-degree window, 30 degrees to either side of the vehicle centerline (Figure 34.17). When sensing is only within this one direction, this is called single-point sensing. Multipoint sensing systems have remote sensors in other vehicle locations. Second-generation systems are able to sense impacts at 90 degrees to either side of the vehicle.

A sensor can be electronic or mechanical. The ball-and-magnet is one type of mechanical sensor (Figure 34.18). The sensing mass is a gold-plated ball that is normally held in place by a magnet. During a crash, the force from the impact breaks the ball away from the magnet, where it completes an electrical circuit between two contacts. The ball only makes electrical contact for a short time before it is drawn back to the magnet once again. The strength of the magnet and the weight of the ball determine the calibration of the sensor. Correct sensor installation in the vehicle is also critical to its calibration.

A different sensor design has a stainless steel ribbon rolled up inside. The sensor is airtight and is filled with nitrogen gas to prevent corrosion. During an impact the ribbon unrolls and closes an electrical circuit. The ribbon rolls back when the force stops.

An electronic accelerometer, sometimes called a strain gauge, is a recent addition to automotive safety

VINTAGE AIR BAGSThe earliest air bags, called fi rst-generation air bags, were fi rst used on vehicles in the late 1980s. General Motors’ (GM’s) computer was called a diagnostic energy reserve module (DERM). The DERM was not required for the deployment of the air bag. Arming and discriminating sensors completed the electrical path for the deployment. Early and late systems have an electrical energy reserve in case the battery becomes disconnected during a crash.

Figure 34.16 (a) A clock spring allows electrical conti-nuity when the steering wheel turns. (b) Bottom and top views of a clock spring.

Clock spring electrical unit

Air bag

(a)

(b)Clockspring

Bottom view Top view

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circuit and deploys the bags. A dual-stage system has twin deployment circuits, so it has a special clock spring.

Collision Sensors. First-generation systems that used electromechanical crash sensors are covered here first. Later systems have improved due to advances in microelectromechanical technology. Most use a single, very sophisticated electronic sensor. These systems are covered later.


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systems. This technology, called micro electromechan-ical systems (MEMS), advanced in the 1990s to the point where it could survive the harsh environment of the automobile. An accelerometer is an electronic sen-sor that can sense impact (Figure 34.19). The MEMS accelerometer senses a net change in forward velocity and can sense up to �90 degrees.

■■ SCIENCE NOTE ■■

MEMS integrates mechanical parts (sensors/actuators) and electronics on a common silicon substrate. This miniaturization is called microfabrication technology. A human hair is 100 microns. The following are sizes of other typical MEMS devices:■ miniature gear — 300 microns diameter■ pressure sensor — 200 microns wide■ resonant gyroscope — 100 microns wide

accelerometer■ angular rate yaw — 50 microns wide

sensor

Biaspermanent magnet

Steel ball

Direction of travel

Electrical contacts

Steel ball

Electrical contacts

Impact

Figure 34.18 A ball-and-magnet sensor at rest and during impact.

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Figure 34.19 An accelerometer registers the force of a collision electronically.

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Figure 34.17 A modern air bag system.

30˚30˚

Coneof influence

Passenger compartment sensor

Driverair bag

Passenger air bag

Impactsensor

Impactsensor

(arming)

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Air Bag Electronic Control Module. The electronic control module used with today’s air bags has become very sophisticated. Early modules only had to deal



with the driver-side air bag. New ones must deal with passenger-side air bags and seat belt pretensioners as well. The module is in the steering wheel with the driver-side air bag and above the glove compartment for a passenger-side air bag.

Squibs. An air bag control module receives input from the impact sensor and matches deployment to the conditions of impact. One or more fuse-like ignition devices called squibs are used in each air bag (Figure 34.20). A squib, sometimes called an initiator or an igniter, is the heating element that ignites the gas-gen-erating material to inflate the bag. It has an electrical igniter and a small explosive charge.

New-Generation Air BagsThe latest air bag systems are called smart restraint systems or third-generation air bags. Smart air bag sys-tems match the speed of deployment, the crash char-acteristics of the vehicle, and the size and weight of the passenger. Multistage systems can have approximately 18 deployment loops with up to six side air bags and seat belt tensioners.

Ultrasonic sensors monitor:■ the front passengers for seat position and weight■ the position of the driver in relation to the steering

wheel■ seat belt usage■ the severity of the crash A multistage ABS, in which air bags can have more than one squib, can infl ate an air bag in stages (Figure 34.21). In a less severe crash, only one of the squibs will be fi red by the computer. In an intermediate col-lision, one squib will fi re, followed by the other a few milliseconds later. In severe impacts, both squibs are fi red at once.

Figure 34.21 A multistage air bag with two squibs.

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Air Bag DeploymentThe deployment process takes about 0.1 second from start to fi nish from the moment a crash is detected. First, the sensors must confi rm that a collision has occurred. On systems with driver-side-only air bags, about 2 amps of current is directed to an igniter. On multiple air bag systems, the sensor signal is evalu-ated by the ECU, which directs electrical current to the correct air bag’s squib. The current heats a fi lament, which ignites a capsule. The heat from the capsule ignites solid pellets, which generate harmless nitrogen gas when they burn. The rapidly expanding gas infl ates the air bag. Remember that this entire process takes about 0.1 second.

The air bag breaks its way through the steering wheel cover or the plastic or fabric dashboard on the passenger side. Following deployment, the air bag begins to defl ate immediately. The harmless gas vents through holes in the back of the bag or through the fabric.

Most systems use a pyrotechnic infl ator that uses sodium azide pellets (rocket fuel) to produce nitrogen gas to fi ll the air bag. Some newer systems use heated gas infl ators (HGI). They use a nontoxic gas (hydro-gen) and air, which turn to water vapor when released after the bag deploys. Other systems use high-pressure stored argon gas to help infl ate the bag. These systems are more common for use in passenger-side air bags. A cross-section cutaway of a hybrid infl ator is shown in Figure 34.22.

A two-stage bag has two chambers with cartridges full of argon gas compressed to 3,000 psi and a solid propellant. When the squib fi res, it ignites the solid propellant in one of the chambers. The rapidly burn-ing propellant heats the cool argon gas, which helps to infl ate the bag. Firing multiple squibs results in even more expansion.

Propagation of fire

Flow of nitrogen gas

To the bag To the bagScreens

Igniter charge

Gas generant pellets

Inflater cross section

Squib

Figure 34.20 A squib fi res the igniter.

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deployment can be violent, especially for smaller pas-sengers and infants. The Federal Motor Vehicle Safety Standard 208 has been amended to protect passengers weighing less than 100 pounds (45 kg) by using a less violent deployment based on the severity of the impact. The safety amendment also specifies that the air bag be disabled when the front seat is occupied by an infant in a rear-facing baby seat or a child weigh-ing less than the average 6-year-old. A warning light must illuminate when the passenger seat is occupied and the air bag is disabled (Figure 34.24).

One method of occupant sensing uses a silicone-fi lled bladder under the seat foam (Figure 34.25). A pressure sensor is connected to the bladder by a hose and the pressure reading is analyzed by the

NOTE: The air bag sensing and diagnostic modules on later vehicles record data during deployment that can be accessed by accident investigators when determining the cause of a collision. Crash event recordings can tell the speed of the vehicle, whether the brakes were applied and antilock brake system (ABS) was engaged, how far the throttle was open and the rpm of the engine, whether the seat belts were in use, and the amount of change in velocity of the vehicle during the crash.

Side Air Bag Deployment. Side air bags (see Figure 34.12) deploy individually when there is an impact on either side of the vehicle but not during a front or rear impact or a rollover. Both side air bags cannot deploy at the same time unless the vehicle is hit from both sides. Side air bags have a single-point sensing system controlled by a side impact module. An accelerometer (see Figure 34.19) is located in the side pillar behind the front door. When an impact of sufficient magni-tude is sensed, the control module supplies the squib with enough current to light it off. When the air bag deploys, it splits the seat back fabric or trim. Unlike front air bags, side air bags are unvented so they deploy three times as fast. Side curtain air bags use the same kind of sensor/controller but are located in the headliner and stretch all along the side of the car (Figure 34.23). They protect passengers from head injuries in a side collision.

Smart Air Bags. The smart air bag system uses various inputs, including speed at impact and passenger body weight and location, to automatically adjust the force of the air bag deployment. It can sense when to step down the force of the deployment. It can also decide that a deployment is not needed.

Occupant Sensing System. One feature of a smart air bag system is the occupant sensor system (OSS), which determines where passengers are located—leaning forward, back, or to the side. It also learns if there is a large or small passenger, or a baby seat, sitting in the front seat on the passenger side. Air bag

Figure 34.22 Cutaway of a hybrid infl ator.

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Side Curtain Air Bags

Figure 34.23 Side curtain air bags protect the heads of the driver and passengers.

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Figure 34.24 A warning light illuminates when the passenger seat is occupied and the air bag is disabled.

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occupant-sensing module. A belt tension sensor, located at the bottom of the seat belt, indicates how tightly the belt has been fastened because a tightly cinched belt around a baby seat can change the weight reading from the bladder and pressure sensor. The occupant-sensing module is sometimes called the occupant classifi cation module.

Another method of weight sensing uses a strain gauge at each corner of the seat frame (Figure 34.26) where they support the seat. A circuit board bonded to each gauge has a metallic foil grid that changes resistance under strain. When the weight on the seat changes, sensor voltage output information to the occupant-sensing module changes as well. Driver- and passenger-side seat track position sensors are also part of some systems. All of this information is analyzed by the computer when it deploys the air bags.

Bladderand sensor

Figure 34.25 An occupant classifi cation system with an integrated electronic control module.

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■■ SCIENCE AND MATH NOTE ■■

Air bag deployment is based on the rate of change in acceleration measured by the accelerometer. The rate of change, called JERK, is mapped through time by a mathematical algorithm. The algorithm, based on a genetic model, is used to make the complex decisions during a crash regarding whether, and how to, deploy the system. The algorithm improves each year as more is learned about crash protection.

The computer repeatedly monitors the acceler-ometer value during fractions of a second. In GM’s system, when an average of four consecutive samples exceeds a force of 1–2 g, the algorithm is enabled and determines whether a deployment should occur. This decision is made very fast (in less than 20 mS). An air bag is usually fully infl ated within 50 mS of impact. A millisecond is 1/1000 of a second. Fully infl ating an air bag in 50/1000 of a second is remarkable.

Although the mathematical calculations regard-ing crashes are becoming more sophisticated with experience, accidents like collisions with a tree or pole are diffi cult for the algorithm to resolve because they provide a slower event. Imagine driving into a saw blade that cuts the car in half but does not provide the accelerometer with a measurable “g” force.

Newer systems are able to consider vehicular forces during a rollover. An angular rate sensor tells how quickly the vehicle is rolling over and how many times it rolls. It includes automatic fuel cutoff and automatic battery disconnect. Current systems allow the air bag to stay infl ated for up to 7 seconds. Chances of a roll-over lasting longer than this are remote.

When a vehicle has a satellite communication sys-tem, computers that are part of the air bag system can sense that an accident has occurred and send emer-gency vehicles to the site.

Radar-based systems can sense when a vehicle will not be able to stop in time to avoid an accident and the computer will begin air bag deployment. The same system is used for adjustable distance cruise control, discussed later.

RESTRAINT SYSTEM SERVICEWhen a vehicle has been in an accident, all of the parts of the passive restraint system will have to be checked. The seat belts are inspected for fraying and ease of operation. Pull the web all the way out of the retractor to give it a thorough inspection. Connect the ends of the buckle to be sure it clicks and releases correctly. If a problem is found, replace the belt assembly.

Check the centrifugal belt retractor by pulling it hard. Centrifugal force should make it catch. The belt should be able to move out of the retractor when it is pulled slowly. A pendulum belt retractor depends on the vehicle stopping quickly to provide inertia to set the belt. During a road test, brake suddenly at a speed over 10 mph to determine if this retractor is working.

Figure 34.26 A strain gauge used at the corners of a passenger seat frame for occupant sensing.

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When seat belts are equipped with pretensioners, you can tell they were deployed if the belts are diffi cult to buckle. A pretensioner that has been deployed must be replaced.

Air Bag ServiceUse the manufacturer’s service and diagnostic informa-tion when servicing air bag systems. A typical informa-tion library will include the system’s components and how they operate. Repair procedures typically provide a chart listing the procedure to follow when making a repair. Detailed wiring diagrams and component locators are also provided. Air bags are explosive devices, so safety precautions are described as well. Cautionary labels can be found in the engine compartment, on the back of sun visors, on the back of the air bag (Figure 34.27), and on the wiring harness (Figure 34.28). Also note that air bag connectors are colored cautionary yellow.

Diagnostic trouble codes can be used to deter-mine the cause of active codes, which are those that illuminate the SRS instrument panel light. Diagnostic trouble codes (DTCs) can also tell you which squibs in a multistage system have fi red. Stored codes can help you determine the cause of an intermittent problem.

Newer systems have special tools that can be sub-stituted for parts of the system to simulate a resistance during testing. A problem can sometimes be isolated by substituting into the circuit a resistance that is known to be good. Be certain that all connectors are in good condition and that none are bent.

One manufacturer’s test sequence calls for remov-ing the air bag and installing a load tool in its place. If the problem exists when the battery is reconnected and the ignition key is turned on, it is not because of the air bag module. The battery should be discon-nected once again and the clock spring disconnected. The load tester is installed in place of the clock spring while the battery is reconnected and the key is ener-gized. If the code is not active any longer, the problem has been isolated to the clock spring.

Many manufacturers have a safety device called a shorting bar that automatically shorts the circuit

when an air bag module connector is disconnected. If the shorting bar does not release as designed, a prob-lem can occur when the connector is reconnected. The air bag will remain short-circuited, and the diagnostic module will set a code and illuminate the air bag light.

When a new computer is installed in a vehicle, it must be programmed with the correct vehicle identi-fi cation number (VIN) or the system will not operate. The VIN tells the computer what type of system is installed in the vehicle. Does it have side air bags, for instance?

Replacing an Air BagAir bags are expensive and cannot be reused once they have been deployed. Many manufacturers stipu-late additional parts to be replaced when an air bag has deployed. If all of the vehicle’s air bags have been deployed, this can be enough to cause an insurance company to declare a vehicle a total loss.

When one air bag deploys but the other does not, both air bags are often replaced because the bag that did not go off could be defective. Some shops explode the replaced undeployed air bag inside a cage.

Sun visor label Air bag module

Air bag cautionlabel

Figure 34.27 Air bag caution labels from the back of a sun visor and on the back of an air bag module.

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Figure 34.28 Air bag wiring harness connectors are colored cautionary yellow.

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An air bag explosion is a violent event. A driver who survives a crash during which an air bag has been deployed often has burn marks on his or her arms from holding the steering wheel when the bag went off. The surface of a deployed bag will be covered with powder and by-products of the chemical reaction. The powder is mostly cornstarch or talc. One of the by-products is sodium hydroxide, or lye. This caustic mixture reacts very quickly with the air to form sodium carbonate and sodium bicarbonate (baking soda). Although it is unlikely that the dust on a deployed air bag will be corrosive, use gloves and goggles to protect yourself just in case.

Figure 34.29 shows the parts of a typical driver-side air bag assembly. Details on air bag care, removal, and disarming are given in Chapter 66. That chapter deals with steering wheel service. It is presented there because all new vehicles are now equipped with air bags.

Air Bag Sensor ServiceAir bag sensors are sensitive to damage from mishan-dling. Do not use an impact wrench around a sensor, and be careful not to drop it. When installing a sensor, it must be positioned so that the arrow on its housing is aimed to the front of the car.

Use caution when adjusting a door strike plate. Hitting the pillar with a hammer while the key is on could deploy a side air bag.

SECURITY, NAVIGATION, AND ELECTRICAL ACCESSORIES

Automobile theft is a serious problem. Security systems have been on automobiles for many years in an effort to make automobile theft more diffi cult. Antitheft devices include locking systems, alarms, and disabling systems.

Door LocksSince the early days of the automobile, locks have been provided for the doors and trunk. Newer sys-tems include electronically coded resistance keys, key-less entry systems, and light delay systems. Internal and external hood locks prevent a thief from gaining

access to the under-hood area. This makes it diffi cult to electrically disconnect an alarm system’s siren or horn. Most cars have a release cable or electrical switch accessed from inside the vehicle to open the fuel fi ller door. This helps prevent the theft of gasoline.

Electric Door Locks. A popular feature on many vehi-cles is electric door locks (Figure 34.30). They can be operated by a switch, but electric door locks also allow manual operation in case of electrical failure. Some cars do not have electric controls on the rear doors, and others only have them on the driver’s door. When they are on all doors, for child safety, the driver’s side has a switch position that makes unlocking of the other doors possible from that seat only. Some doors automatically lock when the shift selector is moved out of the park position, and some engage automati-cally at speeds over 8 mph.

A solenoid or permanent magnet motor operates the locks (Figure 34.31). Large solenoids were used on old cars. Since the mid-1970s, permanent magnet reversible motors have been used to operate the rod that moves the lock. They do not require a ground,

SIR

Air bag module

Igniterassembly

Inflater Air bagassembly

LinerCover

Figure 34.29 Parts of a typical driver-side air bag assembly.

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Door lockcontrolswitch

Door lockactuator

Pushbutton

Figure 34.30 An electric door lock.©

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Figure 34.31 A permanent magnet electric door lock motor, disassembled to show the armature.

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fob receives a radio signal from the computer each time the engine is started. The signal for each car is unique. Otherwise one signal would operate the doors and ignition systems of all cars. To make unique indi-vidual signals, manufacturers use rolling codes. This system changes the frequency transmitted by the key fob every time the lock or unlock switch is activated. The new frequency is stored on the module within the vehicle. The key fob transmits that signal to the vehicle the next time it is used. This prevents car thieves from using a portable electronic device to hack key fob sig-nals. Rolling codes are encrypted with billions of pos-sible codes. The transponder’s signal is different each time the engine starts, but the computer knows what the signal should be. If the signal is not as expected, the starting, fuel, and ignition systems are disabled.

In the unlikely event that a signal is scrambled between the transmitter and control module, the sys-tem will no longer operate. On some systems, holding both the lock and unlock buttons down at the same time for 10 seconds will reset the system and allow the doors to open and the engine to start.

Keyless EntryToday, even the most inexpensive vehicles come with some type of keyless entry system that allows the driver to open the doors or trunk (Figure 34.33). The system uses a key fob transmitter (Figure 34.34) (some Fords use a keypad on the driver’s door). Interior lights and the security alarm are also operated by the transmit-ter. Some systems can open the windows and sunroof, too. Holding down the door unlock key is the usual method of activating this feature.

NOTE: The frequency of keyless entry system transmis-sions is between 300 and 400 megahertz. This is far above the range of audible sound. Therefore, a signal from a key fob cannot be transmitted over a cell phone.

Electronic Key SystemsSome vehicles use an electronic key that transmits a radio frequency to open and close door locks and the trunk. Some have a metal key that slips out of the key fob to operate an ignition switch without conven-tional tumblers. The “key” uses infrared technology to unlock the steering column and start the engine.

Intelligent Key SystemsAn intelligent key, or a smart key, system allows control of engine starting, door unlocking and locking, and seat position adjustment without using a mechani-cal key. This system, found most often on luxury and hybrid vehicles, replaces the traditional key with a smart key and a push-button start switch.

The intelligent key (Figure 34.35) communicates with the intelligent key module in the vehicle when the transponder is within approximately 31.5 inches

because the motor’s polarity switches with the direc-tion of current fl owing through its two wires. The ground connection for the entire system is at the mas-ter door lock switch.

SECURITY SYSTEMSThere are several types of key entry systems, including smart keys with remote engine start capability. Active and passive antitheft systems are covered here as well.

Pass Key SystemsSecurity keys often have a resistor or a transponder to protect against unauthorized copying of the key. Although a replacement key will fi t the lock, the engine will be prevented from starting if the computer does not sense the correct key. With a pass key system, the ignition system cannot be bypassed by “hot-wiring.”

Electronic ValetSome systems have an electronic valet feature. A valet key will unlock the car door and start the engine but will not open the trunk, glove compartment, or console.

Resistance KeyA resistance key is a normal key imbedded with a resistance pellet (Figure 34.32). The computer recog-nizes its small resistance and realizes this is the key that should go with the vehicle. There are several resistance values that can be assigned to the vehicle, and both the resistor and lock tumblers must match. If the resistance is incorrect, the computer opens the starter circuit and will not allow the engine to crank. Depending on the vehicle, it might also disable other systems.

Transponder KeyA transponder key is used in many late-model vehi-cles as a theft deterrent. The transponder in the key

Resistor pellet

Pass key module

Ignition lock

PCM(fuel disable)

Starter

Power feedto solenoid

Frequency link to PCM

Figure 34.32 A resistance key unlocks this security system.

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(80 cm) of the receiving antenna for the driver- and passenger-side doors and the back door (Figure 34.36). Two sensitive outside antennae are located in the mirrors or door handles and there are three inside antennae as well.

NOTE: Smart key operation can be hampered by interfer-ence from powerful electrical generation facilities like elec-trical substations and TV broadcasting.

The intelligent key module identifi es his and hers keys and responds by setting the car seat position and mirrors before the driver enters the vehicle.

Ford has a smart key, called MyKey, that parents can give to younger drivers. The key fob, which looks

Figure 34.34 Examples of keyless entry transmitters.

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Transponderkey fob

Figure 34.35 An intelligent key can automatically open doors or start the engine when it comes within range of the system’s antennae.

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Trunk latch switch

Trunk key switch

Ignition key switch

Driver’s doorlock switch

Keylessreceiver unit

Right reardoor switch

Left reardoor switch

Key cylinder switch

Key cylinder switch

Door lock actuator switch


Door switchDoor lock actuator switch

Door switch


Figure 34.33 A keyless entry system.

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Figure 34.36 An intelligent key system has antennae at each front door and at the back for the trunk or hatchback.

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Illuminated EntrySome vehicles have an illuminated entry feature that turns on the interior lights when the outside door han-dle is moved and the doors are locked. On many vehi-cles, the keyhole in the door also illuminates.

Theft-Warning SystemsVehicle alarm systems are either passive or active. ■ A passive alarm system is “armed” when the

key is removed from the ignition, all the doors are locked, and the hood and trunk are closed.

■ An active alarm system must be turned on. Older systems used the key, a keypad, or a switch. Newer systems are activated by the keyless entry transmitter.

Doors can be locked using the key, the button, or the remote control transmitter. The system can be disarmed only by using the key or remote control. An alarm is triggered if the door, trunk lid, or hood is opened with-out using the key or remote control transmitter.

The alarm system uses several simple mechani-cal switches to provide signals to a computer. Figure 34.38 shows a typical system. The chart lists pin num-bers that would be used with the electrical wiring dia-gram when troubleshooting problems in the system. The switches provide an “on” or “off” ground signal to the computer. When the system is armed, an alarm is triggered if the computer loses a ground signal from any of the switches.

Some systems use ultrasonic motion sensors. A drawback to these systems is that they generate annoy-ing false alarms that can be triggered by someone lean-ing on the vehicle or bumping against it.

identical to a normal key, prevents speeds above 80 mph, and sounds a chime as road speed increases beyond 45, 55, and 65 mph. When the vehicle has been started using MyKey, traction control cannot be disabled. The warning that sounds when the fuel level drops too low comes when estimated time until empty is 75 miles instead of 50. The smart key also limits the volume of the sound system to 44% of its total potential.

Some smart keys, BMW, for instance, have uses outside of the vehicle after unlocking and starting the car. A radio frequency chip in the smart key allows the purchase of fuel, can pay tolls, and can charge pur-chases in grocery stores and restaurants.

The Toyota hybrid smart key system has a steer-ing lock ECU that unlocks the steering wheel using a motor.

Some systems have a mechanical key within the transponder that can mechanically operate the sys-tem. If the battery in the key transponder goes dead while the car is being driven, the engine will continue to run, but it will not restart again after the ignition has been shut off.

Key Fob BatteryThe ECM looks for a signal from the key fob four times every second. To protect the key fob battery from run-ning down when the vehicle is out of use, after 5 days it checks less frequently. If the key fob has not been used within 13 days, it shuts off. Pushing the lock and unlock buttons will bring it back to life.

Smart key battery life expectancy is listed as only 1–2 years, although batteries often last up to 4–5 years. To test the battery charge condition, push the button three times; the battery light should fl ash. The bat-tery in a smart key can discharge if it is within 3 feet (1 meter) of anything that produces electromagnetic waves, including anything that communicates with the Internet.

If the smart key battery is dead, the smart immo-bilizer system can be bypassed by holding the smart key within 1" of the power button. This will allow the engine to start when the button is pressed.

Remote Engine StartingRemote engine starting has long been a popular after-market addition to vehicles, especially in cold climates where it is desirable to have the engine warm and the heater working before entering the vehicle. Intelli-gent key systems can be programmed to allow remote engine starting without installing the key.

NOTE: Add-on features sometimes cause problems when they are not compatible with sophisticated vehicle elec-tronic systems. Original equipment engine starting systems prevent this problem. Aftermarket car alarms have also been known to cause problems with vehicle electronics.

Figure 34.37 shows a schematic for an engine start-ing system.

Intelligentkey

Key ID

Intelligent key unit

Search

Each inside key antenna

Ignition knob switch

Key switch

Steering lock unit

Computer areanetworkcommunication

Combination meter

BCM

Intelligentpowerdistributionmodule

Intelligent key warningbuzzer (instrument panel)

Starter motor

M

Figure 34.37 An intelligent key schematic with engine starting capability.

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Transponder Passive Antitheft SystemsMany vehicles produced since the mid-1990s use similar passive antitheft systems with an encoded transponder ignition key. The following is a generic description of one of the simpler systems.

A transponder, which is an electronic device installed permanently in the key, has its own unique identifi cation code. Each key must be programmed to match the vehicle’s computer before it will start the engine. Also, if a powertrain control module (PCM) is replaced, the engine will not start unless the PCM is reset to match the transponder.

Some manufacturers’ antitheft systems disable the starter motor, whereas others’ do not. Most systems

If the computer determines that the vehicle is being tampered with while the alarm is armed, it will disable the starter and lock the car. Typically, the horn sounds and/or the headlights fl ash for 2 or 3 minutes. The system then resets, provided that the intruder is no longer attempting to enter the car. This prevents the battery from going dead.

NOTE: If the alarm system is accidentally triggered, a typi-cal system can be shut off by turning a key in the door lock.

Some alarm systems are equipped with a “panic” feature. Holding the button down on the remote con-trol will activate the alarm.

The front door key cylinder switches are an impor-tant part of the theft deterrent system. A pair of mag-netic reed switches is mounted on the body of each of the lock cylinders (Figure 34.39). A magnet on the key cylinder sweeps past one of the reed switches when the key is turned to the unlock position. It sweeps across the other one when turned to the lock position. The trunk lock uses a similar system. It puts the system on standby when the trunk is opened with the key while the system is armed. Closing the trunk rearms the system.

If an alarm triggers too easily, check the adjustment and switch position for the door, trunk, or hood. Some systems have a key cylinder tampering switch. This prevents the door or trunk locks from being punched out during a burglary. The switch can also be triggered by unlocking a door with a Slim Jim. A Slim Jim, some-times called a lockout tool, is a long, thin spring steel strip used by towing companies to unlock a car door without using a key. It is slid between the window and its rubber seal. The tool has a hook on one end that a skilled operator can engage with the rod to operate the lock. Newer vehicles often have barriers beneath the window to prevent the use of these tools.

Magnet

Reed switches

Figure 34.39 A door lock switch for an alarm system. When the key is turned, a magnet sweeps across a reed switch to signal the computer that the door is unlocked.

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Attached to keycylinders on the leftand right front doors

29, 30Door keycylinder switches

Reports if door lock is turnedwith the key

Door jambof each door

14, 15, 34Door switches Reports if door is open or closed(shared with dome light)

Switch Pin #s Location Function

Top of inner fender28Hood switch Reports if hood is open or closed

Trunk latch25Trunk switch Reports if trunk is open or closed(shared with trunk light)

Attached to trunkkey cylinder

26Trunk keycylinder switch

Reports if trunk lock is turnedwith the key

Part of door lockactuators in each door

11, 12, 13Door lockactuator switches

Reports if door is lockedor unlocked

Part of ignitioncylinder assembly

23Ignition key“in” switch

Reports if key is in or outof ignition switch

Figure 34.38 An example of a theft-warning system using a series of simple switches as sensors.

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will start the engine for 1 second. A transceiver mod-ule located near the steering column verifi es the signal from the key during the start attempt by comparing it to information stored in nonvolatile memory. If a problem is sensed, the fuel pump and fuel injectors are disabled and the engine dies. Once a car starts and runs for 1 second, the antitheft system is disabled; therefore, if the engine runs for longer than 1 second, the antitheft system is not the cause of engine stalling.

Manufacturers use many variations of this system and diagnosing problems requires a scan tool with dedicated software.

Antitheft System Electrical OperationThe following is an example of how one theft pre-vention system operates. When the vehicle starts, the computer must see a permission code; there are dif-ferent types. A security code, or S Code, is one that is programmed into the key and is stored in the ID code box. A lock code, or L Code, is stored in the steering lock ECU and the ID code box. When there is an elec-trically locked steering wheel, it will not unlock with-out this code. After the S Code and L Code have been met, a 3-bit code enables the fuel and spark to operate effi ciently during engine starting. Finally, a go code, or G Code, allows the vehicle to continue to operate.

Transponder Key ReplacementManufacturers have different processes for replacing keys. All of them are expensive; for example, if you lost all but one key on a Lincoln, you would not be able to make another because you need two keys to program the new one. The car learns the frequency that the key transmits. To program a new key with this system, put the fi rst key in the ignition and cycle it on and off. Cycle the second key and then cycle the new key to program it. Additional keys can be programmed by cycling them at this time.

A vehicle was towed into a shop following a no-start. In the service bay, the vehicle started and the problem would not repeat. The owner’s wife picked up the car and

drove it home without a problem. The next morning, the man attempted to start the car. It would not start, so it was towed once again to the shop. Further investi-gation by the service advisor determined that there was a gasoline speed-pass on the man’s key ring, next to the transponder key. A speed-pass is a transponder as well, and it transmits on the same frequency as the key transponder. When two transponders are on the same key ring, they interfere with each other and the key is disabled. The wife’s key ring did not have a speed-pass, so she was able to drive the car without a problem. A tollway pass can also cause this problem.

CASEHISTORY

CASEHISTORY

VEHICLE TRACKING/NAVIGATION SYSTEMSIn 1993, the United States Air Force launched the 24th Navstar satellite into orbit to complete a network of satellites called the global positioning system (GPS). GPS is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations. The satellites are “man-made stars.” GPS uses these as reference points to calculate positions to closer than 1 centimeter, giving every square meter of the Earth its own address.

Developed by the United States Department of Defense for use at sea during the Cold War, the objec-tive of GPS was to be able to pinpoint the exact posi-tions of nuclear submarines on the surface of the ocean in minutes. The cost of system development was $12 billion.

Some newer vehicles are equipped with naviga-tion systems tracked by the GPS (Figure 34.40). Many navigation systems are incorporated into the radio and use a GPS antenna to provide the exact location of the vehicle. A gyroscope determines when

Figure 34.40 A GPS navigation system can display a vehicle’s exact location.

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Ultrasonic Rear Parking AssistBehind the rear bumper is a blind spot in the driver’s fi eld of rear vision. The blind spot is from about 10 inches above the pavement to the top of the trunk to a depth of up to 5 feet. Rear assist systems operate when-ever a vehicle is in reverse to help a driver determine the distance to a still or moving object when backing (Figure 34.41). It can also help the driver into a tight parking spot, although the system does not detect small objects that are close to the ground. The sensor is hidden in a hole behind the bumper fascia to protect it from low-speed impacts.

Rear assist systems are either ultrasonic or radar based. Radar-based systems can detect objects at greater distances (Figure 34.42), providing a driver with more time to brake. A typical radar-based sys-tem uses dual-beam continuous wave (non-Doppler)

the vehicle is making a turn. Navigation road maps are shown on a thin fi lm transistor (TFT) liquid crys-tal display (LCD) color display. Newer systems can respond to voice prompts using the hands-free phone system.

Many new car systems have special services available by subscription. For instance, roadside assistance is available through the satellite connec-tion when needed. If keys are left in the vehicle, the driver can also call roadside assistance and have the vehicle unlocked. When an air bag is deployed, information is relayed by satellite so police and ambulance agencies can be notifi ed. If a vehicle is stolen, the vehicle-tracking system can pinpoint its exact location.

Night VisionInfrared technology is used to assist a driver in avoid-ing hazards when driving at night. The system can “see” fi ve times farther than the driver can with the headlights on low beam. A camera-like sensor located in the grille reacts to an object’s infrared energy. The computer processes the information and projects it as a video image on the windshield, left of center, through a heads-up display. Warmer objects (people, animals, and moving vehicles) appear light in color or white. Colder objects (sky, signs, and parked vehicles) are darker in appearance.

The night vision feature requires little service. Removal of mud and snow from the camera lens is essential. If the camera requires aiming, refer to the service information for the procedure.

Figure 34.41 Ultrasonic rear parking assist.

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Figure 34.42 A rear assist system calculates the distance to an object.

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radar to monitor an area behind the vehicle approxi-mately 5 meters in depth and 2.1 meters wide. A speed-sensitive algorithm triggers an audible imminent collision warning. Some systems have optional visual alerts, and some smart CAN-based systems can give optional braking commands, too. The distance-based alert changes frequency depending on how close the vehicle is to an object.

Rear View CameraA camera above the license plate in the rear bumper pro-vides backing and parking assistance (Figure 34.43). Some systems project the image on the navigation sys-tem screen, whereas others use a portion of the rear view mirror.

OTHER COMFORT SYSTEMSSome of the following systems are installed on vehicles at the factory, whereas others are installed in the after-market. Aftermarket accessories are not covered by the manufacturer’s warranty. When installed incorrectly, some of these devices can interfere with the vehicle’s electrical system, causing serious hard faults and inter-mittent electrical problems that can void the warranty. Quality grounds must be provided in suffi cient quan-tity. For most devices, the power feed should be fused to an ignition-controlled circuit so power only comes on with the engine on.

Audio SystemsToday’s audio systems are of very high quality due to the advances in electronics but are still made up of the same components as earlier systems: receiver, antenna, amplifi er, and speakers. Today’s systems use electroni-cally tuned receivers (ETRs).

AM Radio. AM stands for amplitude modulation, which varies the strength, or amplitude, of the broad-cast signal. Frequencies range from 550 to 1,600 kilo-

hertz. AM signals bounce off the ionosphere (part of the atmosphere), so they can be received a long distance from where they are transmitted. When the antenna is not of sufficient quality or when the station’s signal is weak, AM is subject to a higher amount of radio fre-quency interference (RFI) than is FM.


The fi rst sound system for a car was the tube-type AM radio in 1929. A hybrid tube-type AM radio with a transistor-type power supply was installed on the 1957 Chevrolet. In the late 1960s, FM began to be the fre-quency of choice. The AM car radio was invented by William Lear, of Lear Jet fame, in the early 1920s. He sold his patent rights to Paul Galvin in 1924. In 1929, Galvin produced the Motorola car radio. The name was developed by combining “motor” and “Victrola.” Philco was another popular make of early radios. By the end of the 1930s, one in fi ve automobiles came equipped with factory-installed AM car radios.


The FM theory was fi rst envisioned by an American named John Carson in 1922. Another man, Howard Armstrong, patented the technology in 1933. Few radio companies were interested in the idea because AM was already well entrenched. The German company Blaupunkt, the mobile elec-tronics division of Robert Bosch, claims to have pro-duced the fi rst FM car radio. FM stereo came of age in the 1960s and was soon being installed in vehicles because of the superior sound quality that it produced.

FM Radio. FM stands for frequency modulation. Whereas AM varies the strength of the broadcast signal, FM varies the frequency of the signal. FM radio signals range between 88 megahertz and 108 megahertz. This frequency is very high compared to AM and is not reflected off the ionosophere. The range of the FM broadcast is restricted to “line-of-sight” distances, typi-cally 35 miles, or more if the station’s signal strength is higher. The signal can be blocked by a hill or a group of buildings. In large cities where the radio signal is strong, the FM waves can bounce off other tall build-ings to provide reception that ordinarily would not be possible.

FM broadcasts are free of RFI noise compared to AM broadcasts. Changes in amplitude (AM radio) are more susceptible to noise interference than changes in frequency (FM radio).

Figure 34.43 A rear view camera provides backing and parking assistance.

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Antenna. A typical electromagnetic radio signal received from the broadcast antenna only has a strength of about 25 microvolts (0.000025 V). Such a small signal requires an antenna to increase its strength. AM radios work best with the longest antenna possible, but FM antennas should be exactly 31 inches (79 centimeters) long. FM windshield antennas are exactly this long. A power antenna that is not achieving its full height of 31 inches will not provide a strong signal to an FM radio. When an antenna is defective, AM reception will suffer most.

Listening to the radio can help determine whether an antenna is good or bad. A bad cable to the antenna will tend to give very poor AM reception, while FM reception will be weaker than normal. If you check the cable with an ohmmeter, it should read infi nite resis-tance between the center antenna case and its center lead. The antenna case must also have a good ground to the vehicle body.

Interference. An antenna picks up different voltages as signal strength varies. Voltage variations can cause radio noise called “whine.” Any device that contains a coil can cause radio interference. The ignition system and the alternating current (AC) generator are pos-sible sources of radio noise. Either of these noises will change in pitch, following variations in engine rpm. A capacitor or a coil-like device called a choke can be installed on the power side connection to reduce or eliminate radio noise. Direct current (DC) generator whine is controlled by installing a choke in series with the power feed to the radio. Ignition noise can be con-trolled by installing a capacitor on the positive side of the ignition coil. The capacitor must be connected to a good ground. Two or more capacitors can be installed in parallel if more capacitance is needed.

Most noise complaints come after the installation of an aftermarket amplifi er, graphic equalizer, or other radio accessory. Antenna amplifi ers or poor ground connections are probable causes of radio noise.

Power Antenna. An electrically powered antenna (Figure 34.44) has an antenna mast attached to a nylon cord. Some power antennas are replaced as a unit. Others have a replaceable cord and mast assem-bly (Figure 34.45).

A power antenna uses a reversible electric motor powered through a relay, most often with a circuit breaker. Most power antennas operate automatically when the radio is turned on. The antenna assembly includes upper and lower limit switches.

To clean a power antenna mast, wipe it with a cloth and then apply oil. Testing is the same as with an ordinary antenna. When testing between the center antenna terminal and the grounded housing, there should be an infi nite ohmmeter reading.

Speakers. Amplified electrical energy from the radio, tape, CD, or mp3 player is turned into acoustical

energy by a speaker (Figure 34.46). A speaker’s sound comes from the vibration of its diaphragm. A perma-nent magnet surrounded by a coil of wire causes the speaker to vibrate in response to the acoustical energy,

Figure 34.44 A power antenna.

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Figure 34.45 A broken electric antenna insert and a new replacement cartridge.

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NOTE: You can usually locate a tweeter by listening, although you often will not be able to find the location of bass speakers.

Midrange speakers produce sound from 400 Hz to 5 KHz. These are relatively easy to locate by listening as well.

Woofer. A woofer produces low-frequency bass sound in the range of 125 Hz or less. It is sometimes called a sub-woofer. Bass sounds are not directional, so you cannot tell where they are coming from. This means they can be located almost anywhere in the vehicle, although they are usually in the rear, where there is more room for them because they are large. There are also midbass speakers that produce frequencies between 100 Hz and 500 Hz.

Coaxial Speakers. A coaxial speaker includes more than one speaker contained within its frame. It has a separate midrange and tweeter to provide a wider frequency range than an ordinary single cone speaker. Triaxial speakers have three speakers within the frame.

Speaker Impedance. Speakers should have the same imped-ance (total resistance in the circuit). If two rear speak-ers each have 6 ohms of resistance, connecting them with parallel wiring will provide 3 ohms of resistance. The front speakers should also have an equal load. Rear speakers are typically bass speakers that have more electrical load. The front speakers can be con-nected in series to raise and balance the load. Connect-ing the rear speakers in parallel will lower the load.

Speaker Wiring. Wires must be large enough to provide the specified power to the speakers. Speaker wire is some-times as small as 22 gauge. A more practical size to use is 14 gauge, especially if larger, higher-impedance speakers might someday be installed on the same wiring.

NOTE: Remember, a lower gauge number, 14 for instance, is a larger wire size.

Soldering the connections ensures a quality connection.

Amplifying DevicesA crossover is a device that blocks certain frequen-cies to a speaker. For instance, to make tweeter cir-cuits more effi cient at producing mid- and high-range sound, a capacitor and coil bass blocker is sometimes used to keep low-frequency sound from reaching the smaller speakers. This is called a high-pass fi lter. A low-pass fi lter is one that passes (transfers) only low-fre-quency sound. Higher frequencies are blocked.

A passive crossover does not use an external power source. An electronic crossover, also called an active crossover, is a more expensive device with fi lters that are powered (amplifi ed). At least two amplifi ers are needed to make an effective active crossover. One amplifi er cov-ers high and midrange; the other is for the woofers.

Making deep bass sounds consumes a large amount of electrical current. A large capacitor is installed in the power line to the amplifi er because battery power is often too slow to respond to the current demand. Remember that a capacitor is a device that stores an

which moves air. The vibration produces pressure waves that make sound.

One speaker is not capable of reproducing sound in the entire range that can be heard by the human ear. Your ear can hear sounds ranging from 20 hertz (cycles per second) at the low end to as high as 20 kilohertz (20,000 Hz). To produce different ranges of sound, different speakers are needed. Figure 34.47 shows the layout for a complete sound system.

Tweeter. A tweeter produces high-frequency sound (4 to 10 kilohertz). Tweeters produce directional sound, which is why they are usually mounted higher on a door panel or on the top of the instrument panel.

2"speaker

2"speaker5" × 7"

speaker

5" × 7"speaker

5" × 7"speaker

5" × 7"speaker

Controlpanel

Electricantenna

Antennalead

Digital CDplayer in trunk

Rear chassisunit

Cell phoneconnection

Figure 34.47 Chart showing the layout of a typical audio system.

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Cone Dome

Connector

Magnet

Voice coil Pole piece

Frame

Figure 34.46 Amplifi ed electrical energy is turned into acoustical energy by a speaker.

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and the antenna is blocked by an overpass or a tall build-ing, a buffer prevents brief disruptions in the service.

MultiplexerWhen different audio sources are to be connected to a radio that does not have multiple accessory plugs, a mul-tiplexer is used. This device allows the addition of inputs like a CD, DVD, satellite radio service, or hands-free cell phone. The multiplexer acts as an electronic switch between the items, sending the signal output to the radio. Figure 34.50 shows a schematic for a multiplexer.

Active Noise CancellationReducing or cancelling unwanted sounds can be done electronically with active noise cancellation. This is accomplished by generating noise of the same fre-quency as the original sound but 180 degrees out of phase, which cancels the noise.

electrical charge. The capacitor, in this case called a power line capacitor, attempts to maintain a consistent voltage level at the amplifi er by discharging current when it senses a demand.

A capacitor must be precharged before installation. Otherwise it will draw too much current and blow the in-line fuse. To precharge the capacitor, follow the instructions that come with it. A typical procedure would be to connect the capacitor’s negative terminal to ground and then connect its positive terminal to a battery with a 12-volt lamp in series between the two. While the capacitor is charging, the 12-volt lamp will be lit. It will go out when the capacitor is fully charged. The capacitor can then be connected to the circuit without blowing the fuse.

Satellite RadioSatellite radio receivers can be original equipment (Figure 34.48) or they can be added to a vehicle in the aftermarket (Figure 34.49). Satellite subscription serv-ice purchased by the vehicle owner is received as a digital signal from an orbiting satellite. The signal is received by a satellite digital audio receiver (SDAR) and is routed by the regular radio amplifi er to the speakers. If the signal is lost, no interference noise is heard. The regular radio will still work, but that mode must be selected fi rst.

A satellite antenna is often located at the center-line of the roof. When communication between the satellite

Figure 34.48 An original equipment radio with satellite capability.

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Figure 34.49 An aftermarket satellite radio.

S &

R P

hoto

Acq

uisi

tion

s, In

c.

SDARreceiver

SDARmultiplexerAntenna

Videoscreen

CD/DVD

Navigationalunit

Hands-freemodule

Radio

AmpSpeakers

Center IP

RF door

RF door

LF door

LF door

RR door

LR door

Subwoofer

Figure 34.50 A multiplexer acts as an electronic switch, sending the selected signal to the radio.

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526 CHAPTER 34

system is capable of recognizing several cell phones from within the vehicle once a phone is paired to the system during a setup process. The hands-free module stores the cell phone’s IP address, and the cell phone learns the module’s IP address.

The radio broadcasts cell phone calls through the vehicle’s audio system. If the radio is already playing, the cell phone has priority. When a cell phone call is begun, the radio stores its volume level and tuning information so it can return to those settings when the call is over. The speaker volume fades and the call is broadcast on the speakers.

The hands-free system is operated using voice recognition software. A microphone module for the system can be located in the mirror, in the center console, or on the dash panel. The module includes the microphone, a preamplifi er, and electronics. The module is adaptive and can learn a voice as it improves system operation.

Complaints of loss of signal are most often related to the service provider. A cell phone’s transmitting power is quite low, usually less than 3 watts. This is possible because of the close proximity of the cel-lular phone network’s antennas. One “cell,” as they are called, transmits to another, and so on. When the distance from the transmitter (cell phone) to the receiver becomes too great, the signal becomes weak or is lost. When the distance doubles, the signal strength becomes one-quarter of what it was.

Electrical interference from the engine and power accessories can cause cell phone problems. Defective spark plug wires will cause a pop heard during conver-sations. Test the operation of the phone with all of the vehicle’s power off to see if a problem goes away.

Rear Window DefoggersMost cars have an electric grid baked onto the rear window. When activated, it warms the glass to above 80°F to melt frost or clear the window of dew. A switch

Sound is a compressed wave in the air. As it is com-pressed, a sound wave gains higher pressure than the surrounding air. This is the positive part of the sound wave. Then it decompresses and becomes less than the surrounding air. This is the negative part of the sound wave. When the positive pressure and negative pres-sure in the sound wave are added to each other in the correct opposite phase, they cancel each other out and the pressure becomes the same as the surrounding air.

Noise cancellation is relatively easy to do with simple sounds. The human voice and other sounds are complex, however, which makes reducing noise more diffi cult. Some sounds are made up of so many different frequencies that they cannot be cancelled out by generating exact opposite sounds. Electronic noise cancellation selects an average of a narrow band of fre-quencies and cancels those noises. Although it is not perfect, it provides a defi nite improvement.

The best noise cancellation can be done when noise is cancelled close to its source. Noise cancelling headsets work well because the sound is contained and cancelled near your ears.

An automobile noise cancellation system uses microphones in the passenger compartment to pick up music from the car stereo as well as any other sounds within the vehicle. The module creates opposite sound waves and transmits them through the passenger com-partment using the speakers in the sound system. This reduces unwanted noise within the car but allows the audio system to work normally.

Active noise cancellation can also generate oppo-site phase noise to the engine drone noise that occurs when an engine idles. It is especially helpful with quieting diesel engine noise. Engine noise can be refi ned to give a diesel engine a high-performance sound or make a small four-cylinder engine sound like a large V8.

DVD SystemsDigital video disc (DVD) systems are available on many vehicles. Some DVD monitors are installed in the rear of a front headrest or seat, but most fl ip down from the ceiling (Figure 34.51). Audio plays through the regu-lar audio system using surround sound when a DVD is playing. This sends more of the sound to the rear of the vehicle.

Jacks often permit connection to video games or video cameras. Wireless headphones are available as well. With headphones, the speakers can play the radio or CDs while the children in the back seat watch and listen to DVDs through the headphones.

Hands-Free Cellular PhonesThere are different types of wireless cellular phone technologies. One type is Bluetooth™, which allows different modules to communicate, such as a cell phone and the on-board receiver in the vehicle. The

Figure 34.51 A DVD system with monitors in the headrests.

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thin, practically invisible metallic coating to be part of the inside of the windshield. Silver bus bars fused to the coating at the top and bottom of the windshield provide power and ground connections (Figure 34.54). A sen-sor that monitors voltage drop within the windshield will shut off power to the circuit if the window has been damaged.

Heated Mirrors. Some vehicles have heated mirrors. They are sometimes tied into the same circuit as a heated windshield or rear window.

Intelligent Windshield Wipers. Intelligent windshield wiper systems that are sensitive to moisture are found on some cars. Rain-sensing wiper systems are covered in Chapter 32.

Power MirrorsPower mirrors are common on many cars. A “joystick” controls both the driver and passenger side mirrors. Each mirror has a dual motor drive, which allows up/down and side/side mirror movement (Figure 34.55).

timer relay controls its operation. The window grid draws a relatively high amount of current, up to 30 amps. When cold, resistance is less so current fl ow is higher. The timer limits “on” time to about 10 min-utes. If needed again, the driver can reset the switch to allow an extra 5 minutes of operation. Figure 34.52 shows a rear defogger circuit. If the vehicle has heated mirrors, they are also activated by the timer switch through a separate fused circuit.

The grid is easily damaged. Damage to the grid can sometimes occur when tape or a decal is removed using a razor or knife blade. The horizontal wires of the grid are connected in parallel, so if one row fails the rest will continue to work.

A short broken section of grid can be repaired using an epoxy repair kit. The kit resembles a bottle of fi ngernail polish and applicator. An epoxy-based liquid that conducts electricity is applied to the break in the grid wire and allowed to dry. Clean the win-dow with alcohol and apply two rows of tape to the window to construct a clean channel for the epoxy to fl ow into (Figure 34.53). Allow 24 hours for the epoxy to cure.

If no part of the grid works, check for power at the grid with a test light or meter. If there is no power, check at the relay timer and switch. Most systems have a lighted switch, which is a pretty good indication of power availability. A bad ground on the side of the grid opposite the power side can also cause the outage.

Some vehicles use the rear window grid as the radio antenna, too. Operation of the radio can be affected when there is damage to the grid.

Heated WindshieldSome newer vehicles are equipped with a self-defrosting windshield that melts ice and frost faster than a con-ventional system that uses air supplied by a blower motor. A wire grid like the one used in the rear glass, would interfere with the driver’s vision. Improved pro-duction techniques in glassmaking allow an extremely

Rear window grid line structure

Fuse

Relay

Off

OnNormal

SwitchB

P

L

Y

Tobattery

Toignition

Indicatinglight

Figure 34.52 A rear defogger circuit.

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Figure 34.53 Repairing a short section of electric grid on the rear window: Apply two rows of tape to the win-dow to construct a clean channel for the epoxy.

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528 CHAPTER 34

measures the intensity of light on the mirror. When the light on the mirror reaches a set point in relation to ambient light, a solenoid moves the mirror to a dif-ferent position.

Power SeatsPower seats allow easy adjustment of seat position (Figure 34.57). Seat position is controlled by switches

Control of the right or left side is selected by rotat-ing the joystick knob clockwise or counterclockwise, or with a separate switch.

Automatic Rear View Mirrors. Some interior rear view mirrors have a directional compass displayed on the lower left corner. Some newer vehicles have electro-chromic or photochromatic mirrors that provide auto-matic, power-free glare reduction like eyeglasses that automatically darken in response to sunlight.

Electrochromic Mirrors. Inside and outside mirrors can be electrochromic. To provide self-dimming in response to glare, automatic day/night inside rear view mirrors have two layers of conductive glass with an electrochromic material sandwiched between. The driver can switch this feature off, except when the transmission is shifted into reverse. Photosensors fac-ing the front and rear adjust the reflection level of the mirror (Figure 34.56). A faulty mirror cannot be serviced but must be replaced.

Automatic Tilt Rear View Mirrors. Some vehicles have inside rear view mirrors that tilt automatically when too much light is reflected into the driver’s eyes. The mirror housing has two photocells: one measures the light within the vehicle (ambient light), and the other

Lower bus

Upper bus Coating

+ –Figure 34.54 A self-defrosting windshield has silver bus bars fused to the coating at the top and bottom of the windshield to provide power and ground connections.

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Lumbarsupportadjuster

Seatbackadjuster

Seatpositionwidth

Figure 34.57 Seat position is controlled by switches or a joystick.

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Mirror glass

Motor

Figure 34.55 Parts of a power mirror.

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Rear facing sensor

Electrical connector

Forward facing sensor Switch

Figure 34.56 An automatic day and night mirror.

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or a joystick. Motors and gear drives are located either under or within the seat. A typical seat uses multi-ple reversible DC motors. The rotating motion of the motor is changed to linear motion to move the seat. The motion of the motor is transmitted to the seat tracks by a steel cable that resembles an older mechani-cal speedometer cable with a very thick steel housing. Some seat drives are rack and pinion, but most are screw driven. Electrically, they operate the same.

Power seats are typically four-way or six-way adjustable, although seats in some luxury cars have more adjustment. In a four-way seat, the entire seat moves up or down and forward or backward. A six-way seat operates in the same way, but it also allows

independent adjustment of front and rear seat height. Up and down adjustment is a desirable feature for taller or shorter individuals. Figure 34.58 shows a schematic of a six-way seat system. Power is supplied to the seats at all times; the ignition key does not need to be turned on.

Four-way systems are used on bench seats; six-way systems tend to be used on bucket or split bench seats. Two motors are usually used for four-way seats. Three are used on six-way seats (Figure 34.59), although some seats use a single motor and a transmission to provide all six movements. Some seats have as many as eight motors to control the six-way functions and also headrest height, seat length, and side bolsters.

Up Dn Frwd Rwd Dn Up Up Dn

Front of seat Entire seat Rear of seat

Right seat control switch

Rd/

Lt B

lu

Bk/

Wt

Bk

Yl/W

t

Rd/

Wt

Yl/L

t Blu

Rd/

Lt G

n

Yl/L

t Gn

Bk/Wt

Bk/Wt

Bk

Left seatcontrol switch(left seat assemblyidentical to right)

CB #12

Rd/

Lt B

lu

Yl/W

t

Rd/

Wt

Yl/L

t Blu

Rd/

Lt G

n

Yl/L

t Gn

CBCBCB

Front heightmotor

Fwd/rwdmotor

Rear heightmotor

Right seat assemblyInsulated side

Ground side

5 6 1 2 3 4 7 8

M M M

Figure 34.58 A schematic for a power seat.

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530 CHAPTER 34

defective. A test light should light up on both sides of the circuit breaker, usually located on the fuse panel. Remove the seat control and check for voltage and ground connections.

Sometimes a power seat problem is not electrical. The causes of the problems vary based on the design of the system. Check the manufacturer’s service informa-tion for details of the repair procedure.

Memory SeatsWhen a vehicle has memory seats, a computer remem-bers the seat position for different drivers. Some com-puters remember the steering wheel position and rear view mirror position as well. Typically, system memory includes the ability to program at least two driver’s seat positions (Figure 34.60). To program the module, the seat is moved to the desired position. Then a button is depressed and held to enter the position into memory. For safety reasons, the power seat memory in many cars only works if the transmission selector is in park or neutral. Be sure the selector is in the correct position if you are reprogramming seat position.

Adaptive SeatsAdaptive seats use memory seat positions but move the adjustment to fi t the driver as she or he shifts in the seat. Some luxury vehicles have massaging seats that move rows of rollers up and down 2" for a few seconds after the driver presses a button.

Adjustable Pedal HeightTo accommodate shorter drivers, some cars have an elec-tric motor–operated assembly that can raise the brake and accelerator pedals up to 3" higher (Figure 34.61). This system can be part of the seat memory as well.

Heated SeatsSome luxury cars have heated seats that warm seat cushions in cold weather (Figure 34.62). A pair of

Troubleshooting Power Seats. Use common sense when troubleshooting electric seats. If only the up and down positioning has failed, check that motor and circuit first. If both seats are not working, look to the power source. The most common problems with power seats are with the switches and motors.

Power is supplied to the seats at all times. If the seats do not operate, fi rst check the fuse or circuit breaker. Most vehicles use circuit breakers because there is a possibility that something could become physically lodged between the seat and the fl oor.

Sometimes the relay clicks when the switch is activated but the seat does not move. This means the breaker is operating but the relay or motor could be

Figure 34.60 Seat memory and adjustment switches. This one has two memory settings.

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TrimotorShield

Driver side shown

Cushion assembly

Shield

Trackassembly

Figure 34.59 A six-way seat with three motors in one unit.

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Bucket seats were used in early airplanes. The name comes from the French word for “cockpit,” which is baquet. Bucket seats became popular in small Euro-pean cars during the late 1940s after World War II. Bench seats had been traditional. However, the location of the gear shifter in the top of the manual transmis-sion, as well as the center parking brake handle, left no room for a middle passenger.



Figure 34.61 Some vehicles have pedal height adjust-ment operated by a motor.

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Head support

Lumbar support air mat

Fans

Fans

Figure 34.62 A seat with adjustable lumbar and head-rest support. The fans are part of the seat’s heating and cooling system.

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■■ SCIENCE NOTE ■■

The Seebeck effect converts differences in heat into elec-tricity. Also called the thermoelectric effect, it is named after the physicist Thomas Johann Seebeck, who dis-covered in 1821 that a voltage developed between two ends of a piece of metal when there was a difference in temperature in the metal. Thermocouple thermometers are based on this principle. In 1834, Jean Peltier discovered the opposite of the Seebeck effect. The Peltier effect is when a difference in heat is created when current is applied to a thermocou-ple. Current passed through the two dissimilar metals of a thermocouple connected at two junctions creates a temperature difference as the current pushes heat from one of the junctions to the other. As one of the junctions cools, the other heats up. In modern applications of the Peltier effect, n-type and p-type semiconductors, used in place of a thermocouple, are connected to each other at the two junctions. When several semiconductors are con-nected to the circuit, the Peltier effect is increased. N-type and p-type semiconductors are covered in Chapter 45.

large resistance wires or more than one multiple heat-ing element is routed through the seat cushions. Acti-vating the seat warmer switch energizes its holding relay, which stays on as long as it remains energized. The relay routes current to heat the seats until the key or switch shuts it off.

When checking for a lack of heating look for power and ground problems, and check the switch and relay. If power reaches the heating element but it does not heat, it has an opening in its circuit and needs to be replaced.

Climate-Controlled SeatsClimate-controlled seats have a seat control unit under the seat. A thermoelectric device heats and also cools the seat (Figure 34.63). The unit does not heat as well as a conventional heating unit, and the circuit has only a 15-amp fuse. A blower motor beneath the seat cush-ion pushes heated or cooled air through perforations

Peltierelements

Climate control fan

Figure 34.63 Seats can be heated and cooled using the Peltier effect.

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in the leather seat, producing a light feeling of air movement (Figure 34.64). The heating and cooling operation of a climate-controlled seat is made possible by the Peltier effect.

Although the Peltier effect is not as effi cient as other heating and cooling methods, Peltier devices are easily adjustable and they are accurate. In climate-controlled seats, the Peltier effect creates a small heat pump using


532 CHAPTER 34

on the driver’s door (Figure 34.67). Power for the individual switches is distributed by the master switch. The two switches are wired in series, so a problem with either of them will prevent the window from operating.

Most systems use permanent-magnet DC motors. These motors can be driven in either direction, depend-ing on the polarity of the wires to the motor. Bat-tery power is supplied to the center of a double-pole, double-throw switch. To operate the window, battery positive (B�) power is directed through the motor from the center terminal and fl ows back to ground through the other side of the switch (Figure 34.68). Moving the switch in the other direction reverses the polarity of the motor to move the window in the opposite direction. The motor is not grounded to the door but receives its ground through a connection at the master switch.

Each motor is protected by its own internal cir-cuit breaker. Problems that can trip a circuit breaker include:■ A window jammed up due from ice formation■ A window out of adjustment in its track■ Binding in a mechanism or track

Some vehicles have a window lock on the master switch activated by the driver that prevents individual switches at the other doors from operating the win-dows. This is a safety feature designed to protect chil-dren. Another safety feature is that power windows can only operate when the ignition switch is in the run or accessory position.

Many power window systems have a time delay that allows windows to be powered for a short time after the engine is shut off. This feature, which allows passengers to close windows prior to leaving the car, is defeated if a door is opened.

Windowmotor

Regulatorassembly

Window

Figure 34.66 The door skin has been removed to reveal the motor and regulator for an electric window.

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Upper junction

Lower junction(a)

Heat

Cooling

(b)

Upper junction

Lower junction

Heat

Cooling

Figure 34.65 The Peltier effect. (a) When current fl ows toward the upper junction it gives off heat as the lower junction absorbs heat. (b) When current is reversed the upper junction absorbs heat as the lower junction gives off heat.

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the same unit to both heat and cool the seat. When current fl ows through the circuit (Figure 34.65), heat is produced at the upper junction and absorbed at the lower junction. Reversing the current fl ow causes the upper junction to absorb heat while the lower junction produces heat.

Power Lumbar SupportsSome seats have power lumbar supports, usually on the driver side. The lumbar area is the lower area of your back. A bladder in the lower seat back is infl ated or defl ated according to commands from the person in the seat (see Figure 34.62).

Power WindowsElectric windows are opened and closed by drive motors. The motors drive a window regulator similar to the ones on hand-crank windows (Figure 34.66). The window regulator, attached to the window, is a gear drive that opens and closes the window. Window adjustments for upper and lower stops and the tilt of the glass are the same as for manual windows.

The motors are controlled by individual switches at each window or by a master switch, usually located

Blowermotor

Figure 34.64 A blower motor beneath the seat cushion pushes heated or cooled air through perforations in the seat.

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get their fi ngers stuck in windows. Some systems sense when the window contacts something, causing it to reverse its operation. Others use an infrared light sen-sor. When the infrared light beam is interrupted by an obstruction, the window reverses direction.

Troubleshooting Electric Window Problems. When trou-bleshooting electric window problems, try all of the windows to see if a problem is something they have in common. An open circuit in one of the control wires from the master switch to a motor can result in a window that operates in only one direction. If one of the directional wires from the window switch to the master switch has an open circuit, the window will not operate at all.

When both rear windows fail to operate, check the circuit for the window lockout. If all windows are not working, check the fuse or circuit breaker fi rst. Then check the ground wire connection at the master switch in the driver’s door panel or below the instrument panel.

When a window does not operate in either direc-tion, a defective motor could be the cause. The circuit breaker could also be opening the circuit if a window is binding in the track. Grab the edge of the window and try to pull it to see if it is free to move. If it is, the window should be able to move the glass.

To test a circuit, verify that both the master switch and the individual switch have voltage. Moving the switch from the up position to the down position should result in a switch of B� (battery positive) from one side of the switch to the other.

After testing the switches, the motor can be tested by jumping its terminals to B� and ground. The window should operate. Reversing the jumper leads

Many vehicles open the driver’s side window all the way when the window switch is held down for more than a third of a second, then released. The window can be stopped anywhere in its travel by depressing the switch once again. An electronic mod-ule energizes a relay to power the motor. When the window reaches its bottom stop, current increases and the module responds by opening the circuit.

Some sophisticated power window systems can sense when something is in the way. This safety fea-ture is especially benefi cial for children, who tend to

B+Ignitionswitch

Windowswitch

Master switchMotor

Figure 34.68 Schematic of a simple power window circuit.

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Passenger'sunderdashfuse/relay box

Masterswitch

Window motors

Window motors

Windowswitch

Windowswitches

Figure 34.67 Parts of a power window system.

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534 CHAPTER 34

should operate the window in the opposite direction. A power probe is handy for this test.

Power door locks are covered earlier in this chapter as part of the security system.

Removing a Door PanelWhen repairing an electric window motor or electric door lock, the inner door panel is removed. This is accomplished by removing the armrest, window crank and door handles, and any other pieces of trim. Window cranks and door handles are retained by either a screw or a clip. A hooked tool or bent wire can be used to pull the clip from its groove (Figure 34.69). To fi nish remov-ing the door panel, pop loose the plastic or metal clips attaching the outside of the door panel to door. There are special tools available for this purpose (Figure 34.70).

NOTE: Door handles sometimes leak. The plastic inside the door panel is important in helping prevent problems from this. Be careful not to damage the plastic.

To locate water leaks, wash the car with soapy water. Then run the air conditioning

(A/C) on full blower to pressurize the cabin. Check for soap bubbles at suspected leak points.

SHOPTIPSHOPTIP

Removing a WindowWhen a window is disconnected from the window frame and hardware, it can fall freely within the window slides. Suction cups are available to hold the window in place while working on the door lock (Figure 34.71).

CRUISE CONTROLMost new vehicles are equipped with a cruise control system capable of maintaining a constant speed above 30 mph without pushing on the accelerator pedal. Vehi-cle speed is controlled from a switch on the steering

Trim clips

Trim clipsTrim clips

Figure 34.70 Removing trim clips. (a) The center pin is pressed into the trim clip to

expand it. (b) A tool for removing a trim clip. (c) The interior panel is removed to allow access.

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Clip

HandleRegulator shaft

Figure 34.69 The window crank is removed by pulling the retaining clip, using a hooked piece of wire or a special tool.

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Figure 34.71 Suction cups are used to hold the window up while working on a window motor.

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VINTAGE CRUISE CONTROLBefore the advent of sophisticated electronic controls, vehicle cruise control systems used a vacuum-operated servo and a transducer. Virtually all vehicles were rear-wheel drive. The transducer sensed road speed by monitoring how fast the driveshaft was turning. Vehicle speed increased in response to vacuum applied to a servo and decreased when vacuum was exhausted.

wheel or at the end of the turn signal lever (Figure 34.72). A light on the instrument panel displays when cruise control is active. Stepping on the brake or clutch pedal deactivates the cruise control, allowing the vehi-cle to decelerate. Selecting “resume” reinstates cruise control to the originally selected vehicle speed.

Coast Accelerate

SetResume

Coast Accelerate

Set Resume

Turn signal lever

MistMist

OffOff

OnOn

LoLoCruiseCruise

WiperWiper

Off On RIA

Off On RIA yytt

eeSS

DDeellaa

PushPush

Hold for coast

Mode control, steering wheel, and on-offrocker switch

Figure 34.72 The cruise control switch on the turn signal lever or steering wheel is used to set speed, accelerate, or resume after braking. The coast position does not apply the brake lights in case a law enforcement vehicle is behind you.

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Electronic Cruise ControlThe electronic cruise control module analyzes and acts on inputs of vehicle speed and engine load. Some vehicles use a stepper motor that pulls on a strap to move the throttle. Many newer vehicles use “drive by wire,” in which the throttle is controlled by a com-puter. These vehicles are basically on full-time cruise control, which is continuously selected by throttle position as the driver moves the gas pedal. Electronic cruise control inputs include a vehicle speed sensor to sense vehicle speed and switches to release the clutch and/or brake (Figure 34.73).

Intelligent Cruise ControlSome newer vehicles have intelligent cruise control, also called adaptive cruise control, that maintains a selected distance from the vehicle ahead dependent on its speed (Figure 34.74). A radar or infrared sensor in the grille of the vehicle detects objects in front and sends a signal to a module (Figure 34.75). An electri-cal diagram of the system is shown in Figure 34.76. The computer can detect a vehicle at up to 390' (120 m) and determine its speed. It applies either the brakes or accelerator to maintain the designed distance. Typi-cal distance settings at 60 mph are 195', 130', and 90'. The brakes can apply at 25% braking power, which is a substantial amount of braking. When the road ahead is clear, the system accelerates once again to the pre-set speed. During slowing, the system illuminates the brake lights. A driver of a vehicle with an intelligent system has the option of using conventional cruise control as well.

There are times when the intelligent cruise control cannot perform all of its duties:■ The system disengages during wet weather

to prevent contamination of the sensor and confusion of the computer.


536 CHAPTER 34

■ Intelligent cruise control performance can be poor on winding roads. The distance sensor has a narrow range of operation so it does not see oncoming vehicles on narrow roads.

■ The sensor can only sense hard objects like a motorcycle but cannot detect soft objects like animals or humans.

Cruise Control ServiceWhen diagnosing cruise control problems, begin by checking the fuse. Check throttle linkage to see that it is not broken or binding up. On older cruise control systems look for damaged vacuum hoses and bad elec-trical connections. Check the driveshaft sensor or vehi-cle speed sensor on the transmission. Service literature for older mechanical cruise control provides instruc-tions for calibration so the vehicle does not accelerate or decelerate too roughly.

Always check the brake lights to see that they illuminate. The brake on and off switch is an essential part of cruise control, and if the brake lights do not work, cruise control cannot operate.

Computer-controlled cruise control diagnosis begins by reading the service information. Next use a scan tool to fi nd defective sensors and switches or to locate a problem in an electrical circuit.

COLLISION AVOIDANCE SYSTEMSCollision avoidance systems use a camera and radar sensors that work with other adaptive cruise control sensor inputs to sense the speed and location of other vehicles (Figure 34.77).

A heads-up dash display and audible alarm warn the driver as the brake support system arms the anti-lock brake system for an emergency stop. When the control module senses the likelihood of a collision and the driver does not react quickly enough, the brakes will apply automatically. Vehicle speed before a colli-sion can be reduced by 5 mph or more. Even a small

Figure 34.74 Adaptive cruise control maintains a selected distance from the vehicle in front.

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Figure 34.75 A sensor located in the grille senses the distance to a vehicle in front and provides information to the control module.

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Coast

Accelerate

Resume

Speed controlswitch assembly

On

Off

Speed control amplifier

Speed control motor

Brake on/offswitch

Vehiclespeed sensor

Connects tothrottle linkage

Figure 34.73 Electronic cruise control inputs include a vehicle speed sensor (VSS) and a brake on/off switch.

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reduction in speed can potentially result in fewer inju-ries to passengers in the vehicle.

LANE DEPARTURE WARNING SYSTEMA lane departure warning (LDW) system uses a camera that sees the lines on the road. A module fl ashes a light and sounds a chime to alert the driver if the vehicle moves too close to the paint stripe marking either edge of the lane. The system does not operate below 45 mph or when the turn signal has been activated on the side of the vehicle that is approaching the paint stripe.

A typical LDW system has a camera lens with a control unit beneath the headliner. LDW is on the

Figure 34.77 A collision avoidance system senses the speed and location of other vehicles and applies the brakes if needed.

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ECM

Distancecontrol ECU

Gateway ECU

Skid controlECU

Meter ECU

Vehicle speedsensor

Stoplightswitch

Acceleratorpedal positionsensor

Cruise controlswitch

Throttle controlmotor

ECT solenoids

Steering sensor

Yaw rate sensor

VSC warningbuzzer

Brake actuator

Steering padswitch

Laser radarsensor

Data bus Data bus

Databus

Databus

Figure 34.76 An electrical schematic of a laser radar system.

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controller area network (CAN) system, so it uses very few wires. Figure 34.78 shows a CAN schematic for an LDW system.

Service to the system is minimal. The calibration process for the camera is done electronically follow-ing service instructions that aim the camera at a tar-get a specifi ed distance to a wall. A scan tool does a self-calibration.

CameraSwitch

Buzzer

Indicator

Turn signal switch

Speedsensor

Controller Area Network

Figure 34.78 A CAN schematic for a lane departure warning system.

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538 CHAPTER 34

position and seat belt usage and adjust the force of the air bag deployment?

9. A sodium azide pyrotechnic inflator produces ____________ gas to fill the air bag.

10. Where is the ground connection for the entire system located on electric window systems?

11. What is the name of the worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations?

12. How much farther can infrared night vision “see” than the driver can with the headlights on low beam?

13. Which kind of radio signal varies the strength of the broadcast signal? What kind varies the frequency of the signal?

14. What kind of radio speaker produces nondirectional sound (you have trouble telling where it comes from)?

15. Which radio speaker is more likely to be located high on a door panel, a woofer or a tweeter?

REVIEW QUESTIONS

1. Automatic seat belts or air bag systems are examples of ____________ restraints.

2. What is a combination lap belt and shoulder belt called?

3. Since the year ____________, supplemental restraint systems have been required on all new cars sold in the United States.

4. The ____________ air bag reduces the risk of the person sliding free under the seat belt and keeps him or her in a better position for protection by a front air bag.

5. The air bag control module has an electrical storage capacitor as a safety backup in the event that the vehicle’s ____________ is damaged in the collision.

6. What is the name of the sensor used to determine that there has actually been a crash?

7. What are three names for the fuse-like ignition device used in an air bag?

8. What is the name of a restraint system with ultrasonic sensors that monitor passenger

1. All of the following are true about cruise control except:

a. Stepping on the brake or clutch pedal will deactivate cruise control.

b. A driver-controlled switch can reinstate cruise control to the originally selected vehicle speed.

c. Adaptive cruise control uses radar or a laser sensor mounted near the rear bumper.

d. On some systems if the brake lights do not work, cruise control cannot operate.

2. Technician A says that FM radio is subject to a higher amount of interference than AM radio. Tech nician B says that the range of the AM broadcast is restricted to “line-of-sight” distances. Who is right?

a. Technician A c. Both A and B

b. Technician B d. Neither A nor B

3. Technician A says that it is rare for both front air bags to deploy together. Technician B says that at least two sensors must say there is a crash before an air bag will be deployed. Who is right?



4. Each of the following statements about antitheft systems is true except:

a. Each key must be programmed to match the vehicle’s computer before it will start the engine.

b. If a PCM is replaced the engine will not start unless the PCM is reset to match the transponder.

c. All manufacturers’ antitheft systems disable the starter motor.

d. If an engine starts and runs for longer than 1 second, the antitheft system is not the cause of engine stalling.

5. Which of the following is/are true about electric seats?

a. Four-way seats usually have two motors.

b. Some six-way seats have one motor.

c. Some seats have eight motors.

d. All of the above

6. Technician A says that window motors must be properly grounded in the door. Technician B says that the polarity of a window motor changes with the direction of current flow through its two wires. Who is right?



ASE-STYLE REVIEW QUESTIONS



9. Two technicians are discussing power seats. Technician A says that most vehicles use a fuse in the power feed to the seat. Technician B says that a four-way seat allows independent adjustment of the front or rear height of the seat. Who is right?



10. Technician A says that electric windows are powered by two switches wired in parallel. Technician B says that a problem with either the window switch or the master switch will prevent the window from operating. Who is right?



7. Technician A says that FM radios need the longest antenna possible. Technician B says that AM antennas should be exactly 31 inches (79 centimeters) long. Who is right?



8. Each of the following statements is true about adaptive cruise control except:

a. A brake switch signal shuts off the cruise control.

b. Adaptive cruise control can apply the brakes.

c. The distance sensor can see oncoming vehicles on narrow roads.

d. The distance sensor cannot detect animals.


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CHAPTER 34 Safety, Security, Comfort Systems, and ...

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