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Chapter 11
Diagnosis and Repair
of Electronic Circuits
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Objectives (1 of 5)
• Explain what is meant by sequential
electronic troubleshooting.
• Perform tests on some key electronic
components including diodes and transistors.
• Define the acronym EST.
• Identify some types of EST in current use.
• Identify the levels of access and
programming capabilities of each EST.
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Objectives (2 of 5)
• Explain why electronic damage may be
caused by electrostatic discharge and by
using inappropriate circuit analysis tools.
• Describe the type of data that can beaccessed by each EST.
• Identify what type of data may be read using
the on-board flash codes.
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Objectives (3 of 5)
• Perform some basic electrical circuitdiagnosis using a DMM.
• Identify the function codes on a typical DMM.
• Test some common input circuit componentssuch as thermistors and potentiometers.
• Test semiconductor components such asdiodes and transistors.
• Describe the full range of uses of a ProLink9000 reader/programmer.
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Objectives (4 of 5)
• Connect a ProLink to the vehicle data bus via
the SAE/ATA data connector and scroll
through the display windows.
• Update a ProLink software cartridge byreplacing the PROM chip(s) or data cards.
• Define the objectives of a snapshot test.
• Outline the procedure required to use a PCand OEM software to read, diagnose, and
reprogram vehicle electronic systems.
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Objectives (5 of 5)
• Understand the importance of precisely
completing each step when performing
sequential troubleshooting testing of
electronic circuits.• Interpret the SAE J1587/1939 codes for
MIDs, PIDs, SIDs, and FMIs using SAE
interpretation charts.• Repair the sealed electrical connectors used
in most electronic wiring harnesses.
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Types of EST
• The term electronic service tool (EST) is generallyused in the trucking industry to cover a range ofelectronic service instruments from on-boarddiagnostic/malfunction lights to sophisticated
computer-based communications equipment.• The use of generic ESTs and procedures will be
reviewed in this section.
• Proprietary ESTs are designed to work with an
OEM’s specific electronics and will not bediscussed in any great detail in this text becausethey are system-specific.
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ATA Connectors
• ESTs capable of reading
ECM data are connected to
the on-board electronics by
means of standard
connectors.• An ATA connector as used
in J1587/1708 system is a
6-pin Deutsch connector.
• The more recent J1939
connector uses a 9-pinDeutsch connector with a
key in the A-pin recess.
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Flash or Blink Codes
• Flash or blink codes are designed to read
active system fault codes.
• Depending on the system, sometimes historic
or inactive codes can also be read.
• Where multiple codes are displayed, OEM
troubleshooting literature should be consulted
because certain types of circuit failure cantrigger codes in functional circuits and
components.
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Using Digital Multimeters (1 of 2)
• Most electronic circuit
testing requires the use
of a DMM.
• This instrument shoulddisplace the analog
multimeter and circuit
test light in the
truck/bus technician’stoolbox.
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DMM Input Terminals
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DMM Rotary Switch
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DMM Pushbuttons
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Using Digital Multimeters (2 of 2)
• Resolution
• Accuracy
• Caution: Whenever a truck circuit has an
electronic control module, ensure that a
digital multimeter (DMM) is used to make
voltage measurements.
– Analog voltmeters can damage ECM circuits.
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Measuring Voltage
• Checking circuit supply voltage is usually one
of the first steps in troubleshooting.
• Voltage measurements determine:
– Source voltage
– Voltage drop
– Voltage imbalance
– Ripple voltage
– Sensor voltages
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DMM Setup for
Making Voltage Measurements
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Measuring Resistance (1 of 2)
• Most DMMs will measure resistance values as lowas 0.1Ω. Some will measure high resistance valuesup to 300MΩ (megohms).
• Infinite resistance or resistance greater than the
instrument can measure is indicated as OL orflashing digits on the display. – For instance, an open circuit would read OL on the
display.
• Resistance and continuity measurements should be
made on open circuits only. – Using the resistance or continuity settings to check a
circuit or component that is energized will damage thetest instrument.
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DMM Setup for Measuring Resistance
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Measuring Resistance (2 of 2)
• Resistance measurements determine:
– Resistance of a load
– Resistance of conductors
– Value of a resistor
– Operation of variable resistors
• Continuity is a quick resistance check thatdistinguishes between an open and a closed circuit.
• Continuity tests determine:
– Fuse integrity
– Open or shorted conductors
– Switch operation
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Diode Testing
• Current flows only when the anode is more positive than thecathode.
• Additionally, a diode will not conduct until the forward voltagepressure reaches a certain value, 0.3V in a silicon diode.
• Some meters have a diode test mode.
– When testing a diode with the DMM in this mode, 0.6V isdelivered through the device to indicate continuity; reversing thetest leads should indicate an open circuit in a properlyfunctioning diode.
• If both readings indicate an open circuit condition, the diode is
open.• If both readings indicate continuity, the diode is shorted.
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Measuring Current (1 of 3)
• Current measurements are made in series,
unlike voltage and resistance readings, which
are made in parallel.
• The test leads are plugged into a separateset of input jacks, and the current to be
measured flows through the meter.
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Measuring Current (2 of 3)
• Current measurements determine:
– Circuit overloads
– Circuit operating current
– Current in different branches of a circuit
• A DMM should have current input fuse
protection of high enough capacity for the
circuit being tested. – This is mainly important when working with
high pressure (220V+) circuits.
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Measuring Current (3 of 3)
• Current probe accessories
– When making current measurements thatexceed the DMM’s rated capacity, a currentprobe can be used. Current probes are notparticularly accurate. There are two types:
• Current transformers – A current transformer measures AC current only. The
output of a current transformer is 1mA per 1A. This
means that a current flow of 100A is reduced to 100mA,which can be handled by most DMMs.
• Hall-effect probe – The output of a Hall-effect probe is 1 mV per ampere. It
will measure AC or DC.
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Breakout Boxes and Breakout “T”s
• The DMM is often used in conjunction with abreakout box or breakout T.
• Breakout devices are designed to be T’ed
into an electrical circuit to enable circuitmeasurements to be made on both closed(active) and de-energized circuits.
• A primary advantage of breakout diagnostic
devices is that they permit the reading of anactive electronic circuit, for instance, while anengine is running.
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Caution
• When a troubleshooting sequence calls forthe use of breakout devices, always use therecommended tool.
• Never puncture wiring or electrical harnessesto enable readings in active or openelectronic circuits.
• The corrosion damage that results from
damaging wiring conduit will create problemslater on and the electrical damage potentialcan be extensive.
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Caution
• The terminals in many connectors are
especially vulnerable to the kind of damage
that can be caused by attempting to insert
DMM probes, paper clips, and otherinappropriate devices.
• Even more important, remember that it is
always possible to cause costly electricaldamage by shorting and grounding circuits in
a separated electrical connector.
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Shop Talk
• When performing a multiple-step, electronic
troubleshooting sequence on a large multi-
terminal connector, photocopy the coded
face of the connector(s) from the servicemanual and use it as a template.
• The alphanumeric codes used on many
connectors can be difficult to read and usinga template is a good method of orienting the
test procedure.
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Diagnostic Connector Dummies
• Diagnostic connector dummies are used to
read conditions in a circuit that has been
opened by separating a pair of connectors.
• The dummies are a means of accessing thecircuitry with a DMM without damaging the
connector sockets and pins.
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Testing Semiconductors
• See Figure 11-11 on page 288 in textbook.
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ProLink 9000
• MPSI ProLink 9000 is a generic reader /programmer EST.
– Access active and historic codes
– Erase historic(inactive) codes
– View all system identification data
– View data on system operation with the engine running or the
truck moving – Perform diagnostic tests on system subcomponents, such assolenoid testing
– Reprogram customer data parameters on engine and chassissystems
– Act as a serial link to connect the vehicle ECM via modem to acentrally located mainframe for proprietary data programming(some systems only)
– Snapshot system data parameters to assist intermittent fault-finding solutions
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Shop Talk
• As truck electronic systems have become more
complex, the limitations of ProLink have made it
much less likely that OEMs will recommend its use.
• Today ProLink will read most systems when
connected to the chassis data bus but may not be
capable of doing much else.
• OEMs tend to recommend PC-based diagnostics
and reprogramming and are therefore less likely tosupport ProLink with the software required to do
anything other than read a system.
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ProLink Data Connection Hardware
ProLink Head Software
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ProLink Head, Software
Cartridge, and Cables
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Multiprotocol Cartridge
• The ProLink MPC(multiprotocol cartridge) isupdated simply by replacingthe MPC card.
• Some of the MPC cards areequipped with a generalheavy-duty reader thatpermits ProLink to read allthe SAE- coded data.
• Replacement of an outdatedMPC card by a current
version means that nocartridge disassembly isrequired to update software. – This simplifies the upgrade
procedure for ProLink datacartridges.
C i
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Caution
• Exercise extreme care when alteringcustomer data.
• Significant performance problems and
component damage may result fromincorrectly programming data to an ECM.
Sh T lk
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Shop Talk
• Always double-check that the password hasbeen correctly input.
• After a password has been input to a system,
no future access can be achieved without it.• Read the number back to yourself to ensure
that it is correctly input.
SAE/ATA
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SAE/ATA
J1587/J1708/J1939 Protocols
• SAE J1587 covers common software protocols.
• SAE J1708 covers common hardware protocols.
• SAE J1939 covers both hardware and software
protocols.• These data bus protocols enable the interfacing of
electronic systems manufactured by different OEMs
on truck and bus chassis, and provide any
manufacturer’s software to be able to read otherOEMs’ electronic systems.
P t l
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Protocols
• Message identifier (MID) is used to describe a major vehicleelectronic system, usually with independent processingcapability.
• Parameter identifiers (PIDs) are usually primary subsystemscommon to all different OEM types covered by the MID.
• Subsystem identifiers (SIDs) describe subsystems that fall withinthe major system (MID) and often include systems orcomponents used specifically by one manufacturer.
• Failure mode indicators (FMIs) are indicated whenever an activeor historic code is read using ProLink or a PC.
– The code actually displayed in the electronic service tool maybe the OEM’s code, but all North American truck electronics useFMIs so system failures can at least be read by theircompetitor’s diagnostic software.
Common MID,
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,
SID, PID, and FMI Codes
• Common MID, SID, PID, and FMI codes areused by all the OEMs manufacturing trucks in
North America.
• Unlike OBD codes in automobiles, whichcover only emissions-related components,
truck data bus codes are fully comprehensive
of all on-board electronic systems and allow
one OEM’s diagnostic instrument to at least
read their competitor’s diagnostic codes.
FMI
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FMIs
• 0 = Data valid but abovenormal operating range
• 1 = Data valid but belownormal operating range
• 2 = Data erratic, intermittent,
or incorrect• 3 = Voltage above normal or
shorted high
• 4 = Voltage below normal orshorted low
• 5 = Current below normal oropen circuit
• 6 = Current above normal orgrounded circuit
• 7 = Mechanical system notresponding properly
• 8= Abnormal frequency, pulsewidth, or period
• 9 = Abnormal update rate
• 10 = Abnormal rate of change• 11 = Failure mode not
identifiable
• 12 = Bad intelligent device orcomponent
• 13 = Out of calibration• 14 = Special instructions
• 15 = Reserved for futureassignment
Electrical Wiring,
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g,
Connector, and Terminal Repair
• Metri-pack Connectors
– Installation of Metri-Pack 150 connectors
– Installation of Metri-Pack 280 connectors
• Deutsch connectors
Splicing Guidelines (1 f 2)
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Splicing Guidelines (1 of 2)
Splicing Guidelines (2 f 2)
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Splicing Guidelines (2 of 2)
• Three-wire splice
– Three-way splice
connectors are
commercially available
to accommodatethree-wire splices.
– The technique is the
same as a single butt
splice connector.
Circuit Symbols and Diagrams
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Circuit Symbols and Diagrams
• The technician shouldbe able to easilyidentify most of thesymbols displayed here
because they are socommonly used.
• They do vary slightlydepending on theOEM. Note the twistedpair symbol used forthe vehicle data bus.
ISO Wiring Codes
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ISO Wiring Codes
• Most manufacturers are either currently usingor plan to use ISO wire color codes on their
chassis electrical systems.
• See Table 11-1 on page 316 of the textbook.
Shop Talk
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Shop Talk
• Diagnostic trees are often used by truck OEMs totroubleshoot malfunctions.
• The “root” of the tree is the problem.
• The “branches” are the various different paths thatcircuit testing will route the diagnostic technician.
• These tests are sometimes referred to as “leaves.”
• Never skip tests or sections within a diagnostic tree.
Some diagnostic trees are driven by OEM softwareand may have hundreds of steps.
Summary (1 of 8)
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Summary (1 of 8)
• The ESTs used to service, diagnose, andreprogram truck engine management systems are
on-board diagnostic lights, DMMs, scanners,
generic reader/programmers, proprietary
reader/programmers, and PCs.
• Flash codes are an on-board method of accessing
diagnostic codes.
– Most systems will display active codes only. Some will
display active and historic (inactive) codes.
Summary (2 of 8)
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Summary (2 of 8)
• ProLink 9000 with the appropriate OEMsoftware cartridge has become the industry
standard portable shop floor diagnostic and
customer data programming EST.• Most OEMs use the PC and proprietary
software as their primary diagnostic and
programming EST.
Summary (3 of 8)
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Summary (3 of 8)
• ESTs designed to connect with the vehicleECM(s) do so via the SAE/ATA J708/1939connector.
• Most electronic circuit testing requires theuse of a DMM.
• Continuity is a quick resistance check thatdistinguishes between an open and a closed
circuit.• A dark band identifies the cathode on a
diode.
Summary (4 of 8)
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Summary (4 of 8)
• Circuit resistance and voltage are measuredwith the test leads positioned parallel to the
circuit.
• Direct measurement of current flow isperformed with the test leads located in
series with the circuit.
• A Hall-effect probe can be used toapproximate high current flow through a DC
circuit.
Summary (5 of 8)
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Summary (5 of 8)
• The ProLink 9000 EST is used to accessactive and historic codes, read system
identification data, perform diagnostic testing
of electronic subcomponents, reprogramcustomer data, act as a serial link for
mainframe linkage, and perform snapshot
data analysis.
• A ProLink OEM software cartridge is updated
by replacing the PROM chips.
Summary (6 of 8)
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Summary (6 of 8)
• A snapshot test is performed to analyze multipledata frames before and after a trigger, usually a
fault code or manually keyed.
• SAE J1587 and J1939 codes and protocols
numerically code all on-board electronic systems,parameters, and failure modes.
• Most truck manufacturers have made the PC their
primary reader, programming, and diagnostic EST
but some sub-system manufacturers still require the
use of a proprietary reader programmer.
Summary (7 of 8)
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Summary (7 of 8)
• The PC is connected to the vehicle data busby means of a 6- or 9-pin connector knownas an ATA connector.
• Once connected, the OEM softwareaccesses the appropriate MID so that thesystem can be read and diagnosed.
• Technicians should remember that any
system using J1587 or J1939 protocols canat least be read using simple general heavy-duty software.
Summary (8 of 8)
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Summary (8 of 8)
• System parameter (PID) failures areidentified by FMIs, making circuit diagnosis
easy.
• Sealed electronic circuit connectors must beassembled using the correct OEM tooling
and components.