Download Heavy Duty Truck Systems Chapter 11

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 be
accessed 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 circuit
diagnosis using a DMM.
• Identify the function codes on a typical DMM.
• Test some common input circuit components
such as thermistors and potentiometers.
• Test semiconductor components such as
diodes and transistors.
• Describe the full range of uses of a ProLink
9000 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 by
replacing the PROM chip(s) or data cards.
• Define the objectives of a snapshot test.
• Outline the procedure required to use a PC
and 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 generally
used in the trucking industry to cover a range of
electronic service instruments from on-board
diagnostic/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 be discussed
in any great detail in this text because they 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 6pin Deutsch connector.
• The more recent J1939
connector uses a 9-pin
Deutsch 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 can
trigger codes in functional circuits and
components.
Using Digital Multimeters (1 of 2)
• Most electronic circuit
testing requires the use
of a DMM.
• This instrument should
displace the analog
multimeter and circuit
test light in the
truck/bus technician’s
toolbox.
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 low
as 0.1Ω. Some will measure high resistance values
up to 300MΩ (megohms).
• Infinite resistance or resistance greater than the
instrument can measure is indicated as OL or
flashing 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 the
test 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 that
distinguishes 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 the
cathode.
• Additionally, a diode will not conduct until the forward voltage
pressure 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 is
delivered through the device to indicate continuity; reversing the
test leads should indicate an open circuit in a properly
functioning 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 separate
set of input jacks, and the current to be
measured flows through the meter.
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.
Measuring Current (3 of 3)
• Current probe accessories
– When making current measurements that
exceed the DMM’s rated capacity, a current
probe can be used. Current probes are not
particularly 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 a
breakout box or breakout T.
• Breakout devices are designed to be T’ed
into an electrical circuit to enable circuit
measurements 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 an
active electronic circuit, for instance, while an
engine is running.
Caution
• When a troubleshooting sequence calls for
the use of breakout devices, always use the
recommended tool.
• Never puncture wiring or electrical harnesses
to enable readings in active or open
electronic circuits.
• The corrosion damage that results from
damaging wiring conduit will create problems
later on and the electrical damage potential
can 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 other
inappropriate devices.
• Even more important, remember that it is
always possible to cause costly electrical
damage by shorting and grounding circuits in
a separated electrical connector.
Shop Talk
• When performing a multiple-step, electronic
troubleshooting sequence on a large multiterminal connector, photocopy the coded face
of the connector(s) from the service manual
and use it as a template.
• The alphanumeric codes used on many
connectors can be difficult to read and using
a 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 the
circuitry 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 as
solenoid testing
– Reprogram customer data parameters on engine and chassis
systems
– Act as a serial link to connect the vehicle ECM via modem to a
centrally located mainframe for proprietary data programming
(some systems only)
– Snapshot system data parameters to assist intermittent faultfinding 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 to
support ProLink with the software required to do
anything other than read a system.
ProLink Data Connection Hardware
ProLink Head, Software
Cartridge, and Cables
Multiprotocol Cartridge
• The ProLink MPC
(multiprotocol cartridge) is
updated simply by replacing
the MPC card.
• Some of the MPC cards are
equipped with a general
heavy-duty reader that
permits ProLink to read all
the SAE- coded data.
• Replacement of an outdated
MPC card by a current
version means that no
cartridge disassembly is
required to update software.
– This simplifies the upgrade
procedure for ProLink data
cartridges.
Caution
• Exercise extreme care when altering
customer data.
• Significant performance problems and
component damage may result from
incorrectly programming data to an ECM.
Shop Talk
• Always double-check that the password has
been 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
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 other
OEMs’ electronic systems.
Protocols
• Message identifier (MID) is used to describe a major vehicle
electronic system, usually with independent processing
capability.
• Parameter identifiers (PIDs) are usually primary subsystems
common to all different OEM types covered by the MID.
• Subsystem identifiers (SIDs) describe subsystems that fall within
the major system (MID) and often include systems or
components used specifically by one manufacturer.
• Failure mode indicators (FMIs) are indicated whenever an active
or historic code is read using ProLink or a PC.
– The code actually displayed in the electronic service tool may
be the OEM’s code, but all North American truck electronics use
FMIs so system failures can at least be read by their
competitor’s diagnostic software.
Common MID,
SID, PID, and FMI Codes
• Common MID, SID, PID, and FMI codes are
used by all the OEMs manufacturing trucks in
North America.
• Unlike OBD codes in automobiles, which
cover 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.
FMIs
• 0 = Data valid but above
normal operating range
• 1 = Data valid but below
normal operating range
• 2 = Data erratic, intermittent,
or incorrect
• 3 = Voltage above normal or
shorted high
• 4 = Voltage below normal or
shorted low
• 5 = Current below normal or
open circuit
• 6 = Current above normal or
grounded circuit
• 7 = Mechanical system not
responding properly
• 8= Abnormal frequency, pulse
width, or period
• 9 = Abnormal update rate
• 10 = Abnormal rate of change
• 11 = Failure mode not
identifiable
• 12 = Bad intelligent device or
component
• 13 = Out of calibration
• 14 = Special instructions
• 15 = Reserved for future
assignment
Electrical Wiring,
Connector, and Terminal Repair
• Metri-pack Connectors
– Installation of Metri-Pack 150 connectors
– Installation of Metri-Pack 280 connectors
• Deutsch connectors
Splicing Guidelines (1 of 2)
Splicing Guidelines (2 of 2)
• Three-wire splice
– Three-way splice
connectors are
commercially available
to accommodate
three-wire splices.
– The technique is the
same as a single butt
splice connector.
Circuit Symbols and Diagrams
• The technician should
be able to easily
identify most of the
symbols displayed here
because they are so
commonly used.
• They do vary slightly
depending on the
OEM. Note the twisted
pair symbol used for
the vehicle data bus.
ISO Wiring Codes
• Most manufacturers are either currently using
or plan to use ISO wire color codes on their
chassis electrical systems.
• See Table 11-1 on page 316 of the textbook.
Shop Talk
• Diagnostic trees are often used by truck OEMs to
troubleshoot malfunctions.
• The “root” of the tree is the problem.
• The “branches” are the various different paths that
circuit 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 software
and may have hundreds of steps.
Summary (1 of 8)
• The ESTs used to service, diagnose, and
reprogram 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)
• ProLink 9000 with the appropriate OEM
software 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)
• ESTs designed to connect with the vehicle
ECM(s) do so via the SAE/ATA J708/1939
connector.
• Most electronic circuit testing requires the
use of a DMM.
• Continuity is a quick resistance check that
distinguishes between an open and a closed
circuit.
• A dark band identifies the cathode on a
diode.
Summary (4 of 8)
• Circuit resistance and voltage are measured
with the test leads positioned parallel to the
circuit.
• Direct measurement of current flow is
performed with the test leads located in
series with the circuit.
• A Hall-effect probe can be used to
approximate high current flow through a DC
circuit.
Summary (5 of 8)
• The ProLink 9000 EST is used to access
active and historic codes, read system
identification data, perform diagnostic testing
of electronic subcomponents, reprogram
customer 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)
• A snapshot test is performed to analyze multiple
data 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)
• The PC is connected to the vehicle data bus
by means of a 6- or 9-pin connector known
as an ATA connector.
• Once connected, the OEM software
accesses the appropriate MID so that the
system can be read and diagnosed.
• Technicians should remember that any
system using J1587 or J1939 protocols can
at least be read using simple general heavyduty software.
Summary (8 of 8)
• System parameter (PID) failures are
identified by FMIs, making circuit diagnosis
easy.
• Sealed electronic circuit connectors must be
assembled using the correct OEM tooling
and components.