Wide-band Air Fuel SensorWide-range, WRAF Wide-band, WAFRLinear Air Fuel, A/FLean Air/Fuel, LAFAir Fuel Ratio Sensor, AFS

Wide-Band Oxygen Sensorallows engines to operate as;Lean as 23:1 (40:1)Rich as 10:1While maintaining closed-loop operation.more accurately reflects the oxygen content in the exhaust vs a conventional oxygen sensor.

Comparison of signalsRegular O2 sensor only measures in a narrow band at 14.7:1Worthless for low emission vehicles!

Wideband has a much wider band to measure from 10:1 to 20:1Necessary for the new direct injection fuel systemsNecessary for clean air!

OperationOxygen causes the Nernst cell to generate a voltage just like an ordinary O2. The oxygen PUMP Cell compares the change in voltage to the control voltage from the PCM, balances to maintain an internal oxygen balance. CURRENT FLOW is altered creating a positive or negative current signal that indicates the exact air/fuel ratio of the engine.The current flow isn't much, usually only about 0.020 amps or less. PCM converts the current output into a voltage signal to be read on a scan tool.Amperage flows here!

Comparison of signalsRegular o2 outputs voltage

WRAF outputs CURRENT

OperationThe volume ratio at 1 bar air-pressure would be about 4500 liter air for 1 lb of fuel.1 bar is 14.5 psi.

an oxygen pump pulls oxygen from the exhaust into a diffusion gap to maintain a constant Voltage.Creating AMPERAGE! .020 ampsCurrent Flows! to maintain voltage!Voltage created by PCM for the scan tool!

When the air-fuel ratio is lean, the sensor produces a positive current ranges from zero to 2.0 milliamperes as the mixture gets leaner up to 22:1, or leaner. (2.2 bar is 31.9:1)

Testing a wide-band oxygen sensor usually involves using a scan tool.

Amperage!Neat Russian Graphics!

Lean Air-Fuel Ratio Sensors May uses 4, 5, 6, or 7 wires. Power wire 1 or 2 wires for the electric heater (power & ground) 3 or 4 sensor wiresNumber of WiresCurrent

LAF Conversions - OBDII ScannersMost PCMs display the rich and lean status of the exhaust, BE CAREFUL! many show the operation of the oxygen sensor in millivolts from zero to 1000 just as if the sensor were a conventional zirconia oxygen sensor. But it is not the actual sensor data.

Normalized OBDII Voltage is the data the PCM will show the scan tool - It is not an actual measurement

Hondas

Looks like regular O25 wires or 6Dual Nernst Cell1200F operation tempRecommends scan tool for diagnosis

Toyota A/FS -Linear A/F 4 Wire1996 appearanceLooks like regular O24 wiresSingle Nernst Cell1200F operation tempRecommends scan tool for diagnosis

Linear A/F signalsHeater pulse widthVoltage reference signals 3.3v & 3.0vLambda value compared to rich lean Substituted HO2S values - slow & minimal movement.

Toyota Testinga. Disconnect the A/F sensor connector.b. measure the resistance between terminals +B and HT. Resistance: 0.8 - 1.4* ohms at 20C (68F). 2007 FJ 1.8 - 3.4 ohmsIf the resistance is not as specified, replace the sensor.Torque: 44 Nm (440 kgf.cm, 31 ft.lbf)c. Reconnect the A/F sensor connector.

Toyotas sensor output is not a changing analog voltage, but rather a small (< 0.020 amps) bi-directional current.RICH exhaust produced a positive 4.89 milliamps a LEAN exhaust produced a negative 1.53 milliamps. The sensor has two signal lines. One line has 3.3 volts, and the other has 3.0 volts on it (relative to engine ground).These two voltages do not change. Voltage (300 millivolts) across the sensors two signal lines does not change.

LEAN Negative AmperageRICH Positive Amperage

Toyotas Intelligent TesterA/F CONTROL Change injection volume Lower 12.5 % or increase by 25 % test at less than 3,000 rpm A/F CONTROL enables checking and graphing of A/F(Air Fuel Ratio) sensor and Heated Oxygen (HO2) sensorvoltage outputs To conduct test, select following menu items:ACTIVE TEST / A/F CONTROL / USER DATA /AFS B1S1 and O2S B1S2,and press YES and ENTER

Verify Proper Operation - Toyota A/FS

Bosch Air Fuel SensorPorsche says all 2010 models will be equipped with the new sensor!Diagnose with Factory scan tool.Compare lambda values on scan tool and emissions machineWatch valuseCreate RICHCreate LEAN

Testing a Bosch compare Lambdathe Best way to diagnose this A/F ratio sensor Scan tool & Gas Analyzer,

Lambda values should should match, if notmore diagnostics will be required.

Testing a BoschCheck Heater Circuit for Current or VoltageDisconnect harness, check resistance of the trimming resistor, located on Input and Output pump current wires. Bosch spec is 30 - 300 ohms.Reconnect harness , use DVOM check reference ground, Bosch spec is 2.4 - 2.7 volts (refer to actual specs)Heater Circuit pattern

Testing a Bosch4. Scope the pump cell & Nernst signal use sensor reference ground that you just checked. Set scope to AC-coupled mode to see negative swingsNernst voltage signal remains at .45 volts at all timesPump cell voltage should vary about .5 to .6 volts switching across 0 volts Drive fuel mix rich then lean expect change in voltage of greater than 1.0 volts.

Pump cell pumps oxygen ions from one side of the sensor to the other. PCM monitors the Nernst signal attempting to keep the voltage at .45 volts. PCM will increase and decrease the current flow to the pump cell to maintain that voltage level.Current pump sensor60 seconds of road test after replacement shows proper operationCheck Mode 6 DataVerify Proper Operation - Bosch LSU 4

Nissan Maxima 2004

Infiniti 2008 EX35

Tech TipsTECH TIPSHonda 5-wire "Lean Air Fuel" (LAF) sensors, the 8-pin connector pin for the sensor contains a special "calibration" resistor. The value of the resistor can be determined by measuring between terminals 3 and 4 with an ohmmeter, and will be 2.4K ohms, 10K ohms or 15k ohms depending on the application. If the connector is damaged and must be replaced, the replacement must have the same value as the original. The reference voltage from the PCM to the sensor on these engines is 2.7 volts.Saturn also uses a special trim resistor in the WRAF sensor connector (pins 1 & 6). The resistor is typically 30 to 300 ohms. The PCM supplied reference voltage is 2.4 to 2.6 volts. If a WRAF sensor has failed because of coolant contamination, do not replace the sensor until the leak has been repaired. The new sensor will fail otherwise.Some early vehicle systems caused a "simulated" voltage to be displayed on a scan tool. The actual value was divided by 5 to comply with early OBD II regulations. Those regulations have since been revised, but be aware if you get a "funky" display on your scan tool

Tech tips continuedvariable current signal that can travel in one of two directions (positive or negative). The signal gradually increases in the positive direction when the air/fuel mixture becomes leaner. At the "stoichiometric" point when the air/fuel mixture is perfectly balanced (14.7 to 1), the current flow stops and there is no current flow in either direction. And when the air/fuel ratio becomes progressively richer, the current reverses course and flows in the negative direction.The PCM sends a control reference voltage (typically 3.3 volts on Toyota applications, 2.6 volts on Bosch and GM sensors) to the WRAF sensor through one pair of wires, and monitors the sensor's output current through a second set of wires. The sensor's output signal is then processed by the PCM, and can be read on a scan tool as the air/fuel ratio, a fuel trim value and/or a voltage value depending on the application and the display capabilities of the scan tool.For applications that display a voltage value, anything less than the reference voltage indicate a rich air/fuel ratio while voltages above the reference voltage indicates a lean air/fuel ratio. On some of the early Toyota OBD II applications, the PCM converts the WRAF sensor voltage to look like that of an ordinary oxygen sensor (this was done to comply with the display requirements of early OBD II regulations).

ReferencesSupersniffers: Why Air/Fuel Ration SensorsBob Pattengale, MOTOR.com Dec. 2005FJ Cruiser Service Manual, 2007, section ES-313ATTS Training, Import Computers, 2008Sam Bell, Ralph Birnbaum & G Jerry TrugliaAdvanced Engine Performance Diagnostics, Halderman, 4th ed. 2009.Alflash.com.ua photos by al tech pageToyota Wide Range Air:Fuel Sensor, John Thornton, Underhood Service, January 2002

44The voltage measured at the A/F sensor will remain constant and will not match the scan tools display. The Voltage shown on the scan tool is created by the PCM for OBDII Diagnostics. Amperage is the measurement!4444