Chapter 11 Bennet

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Chapter 11

Diagnosis and Repair

of Electronic Circuits



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.



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.



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.



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.



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.



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.



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.



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.



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.



DMM Input Terminals



DMM Rotary Switch



DMM Pushbuttons



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.



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



DMM Setup for

Making Voltage Measurements



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.



DMM Setup for Measuring Resistance



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



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.



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.




• 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.




• 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.



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.



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.



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.



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.



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.



Testing Semiconductors

• See Figure 11-11 on page 288 in textbook.



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



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.



ProLink Data Connection Hardware

ProLink Head Software



ProLink Head, Software

Cartridge, and Cables



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



Caution

• Exercise extreme care when alteringcustomer data.

• Significant performance problems and

component damage may result fromincorrectly programming data to an ECM.

Sh T lk



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



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



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,



,

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



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,



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)



Splicing Guidelines (1 of 2)

Splicing Guidelines (2 f 2)



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



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



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



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)



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)



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)



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)



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)



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)



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)



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)



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.

Chapter 11 Bennet

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