phone ISUZU TF SERIES 2004 Workshop Manual

8A-420 ELECTRICAL-BODY AND CHASSIS


No. Connector face No. Connector face
B-55
White
J/B I3 B-65
SilverWeld splice 2 (Ground)
B-56
White
J/B I4 B-66
White44 switch
B-57
White
HVAC control unit B-67
(6VE1)
BlackCruise main
B-58
Black
Check connector B-68
(6VE1)
(4JH1-TC)
Immobilizer
B-59
White
Combination switch-A B-69
Door lock switch
B-60
White
Combination switch-B B-70
(6VE1)
(4JH1-TC)
Immobilizer Coil
B-61
Black
Flasher relay B-71
YellowHorn
B-62
White
Ignition switch (IGSUB : G1) B-72
YellowSRS
B-63
White
Ignition switch (IGSUB : G2) B-73
BlackWeld Splice 3
B-64
Silver
Weld splice 1 (Illumination) B-74
WhiteCellular phone

4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS 6E–79
–Are there areas subjected to vibration or
movement (engine, transmission or
suspension)?
–Are there areas ex posed to moisture, road salt
or other corrosives (battery acid, oil or other
fluids)?
–Are there common mounting areas with other
systems/components?
–Have previous repairs been performed to wiring,
connectors, components or mounting areas
(causing pinched wires between panels and
drivetrain or suspension components without
causing and immediate problem)?
–Does the vehicle have aftermarket or dealer-
installed equipment (radios, telephone, etc.)
Step 2: Isolate the problem
At this point, you should have a good idea of what could
cause the present condition, as well as could not cause
the condition. Actions to take include the following:
Divide (and separate, where possible) the system or
circuit into smaller sections
Confine the problem to a smaller area of the vehicle
(start with main harness connections while removing
panels and trim as necessary in order to eliminate
large vehicle sections from further investigation)
For two or more circuits that do not share a common
power or ground, concentrate on areas where
harnesses are routed together or connectors are
shared (refer to the following hints)
Hints
Though the symptoms may vary, basic electrical failures
are generally caused by:
Loose connections:
–Open/high resistance in terminals, splices,
connectors or grounds
Incorrect connector/harness routing (usually in new
vehicles or after a repair has been made):
–Open/high resistance in terminals, splices,
connectors of grounds
Corrosion and wire damage:
–Open/high resistance in terminals, splices,
connectors of grounds
Component failure:
–Opens/short and high resistance in relays,
modules, switches or loads
Aftermarket equipment affecting normal operation of
other systems
You may isolate circuits by:
Unplugging connectors or removing a fuse to
separate one part of the circuit from another part
Operating shared circuits and eliminating those that
function normally from the suspect circuit
If only one component fails to operate, begin testingat the component
If a number of components do no operate, begin tests
at the area of commonality (such as power sources,
ground circuits, switches or major connectors)
What resources you should use
Whenever appropriate, you should use the following
resources to assist in the diagnostic process:
Service manual
Technical equipment (for data analysis)
Ex perience
Technical Assistance
Circuit testing tools
5d. Intermittent Diagnosis
By definition, an intermittent problem is one that does
not occur continuously and will occur when certain
conditions are met. All these conditions, however, may
not be obvious or currently known. Generally,
intermittents are caused by:
Faulty electrical connections and wiring
Malfunctioning components (such as sticking relays,
solenoids, etc.)
EMI/RFI (Electromagnetic/radio frequency
interference)
Aftermarket equipment
Intermittent diagnosis requires careful analysis of
suspected systems to help prevent replacing good
parts. This may involve using creativity and ingenuity to
interpret customer complaints and simulating all
ex ternal and internal system conditions to duplicate the
problem.
What you should do
Step 1: A cquire information
A thorough and comprehensive customer check sheet
is critical to intermittent problem diagnosis. You should
require this, since it will dictate the diagnostic starting
point. The vehicle service history file is another
source for accumulating information about the
complaint.
Step 2: A nalyze the intermittent problem
Analyze the customer check sheet and service history
file to determine conditions relevant to the suspect
system(s).
Using service manual information, you must identify,
trace and locate all electrical circuits related to the
malfunctioning system(s). If there is more than one
system failure, you should identify, trace and locate
areas of commonality shared by the suspect circuits.

6E–82 4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS
GENERAL SERVICE INFORMATION
Serviceability Issues
Non-OEM Parts
All of the OBD diagnostics have been calibrated to run
with OEM parts. Accordingly, if commercially sold
sensor or switch is installed, it makes a wrong diagnosis
and turns on the check engine lamp.
Aftermarket electronics, such as cellular phones,
stereos, and anti-theft devices, may radiate EMI into the
control system if they are improperly installed. This may
cause a false sensor reading and turn on the check
engine lamp.
Poor Vehicle Maintenance
The sensitivity of OBD diagnostics will cause the check
engine lamp to turn on if the vehicle is not maintained
properly. Restricted oil filters, fuel filters, and crankcase
deposits due to lack of oil changes or improper oil
viscosity can trigger actual vehicle faults that were not
previously monitored prior to OBD. Poor vehicle
maintenance can not be classified as a “non-vehicle
fault”, but with the sensitivity of OBD diagnostics,
vehicle maintenance schedules must be more closely
followed.
Related System Faults
Many of the OBD system diagnostics will not run if the
ECM detects a fault on a related system or component.
Visual/Physical Engine Compartment
Inspection
Perform a careful visual and physical engine
compartment inspection when performing any
diagnostic procedure or diagnosing the cause of an
emission test failure. This can often lead to repairing a
problem without further steps. Use the following
guidelines when performing a visual/physical
inspection:
Inspect all vacuum hoses for punches, cuts,
disconnects, and correct routing.
Inspect hoses that are difficult to see behind other
components.
Inspect all wires in the engine compartment for
proper connections, burned or chafed spots, pinched
wires, contact with sharp edges or contact with hot
exhaust manifolds or pipes.
Basic Knowledge of Tools Required
NOTE: Lack of basic knowledge of this powertrain
when performing diagnostic procedures could result in
an incorrect diagnosis or damage to powertrain
components. Do not attempt to diagnose a powertrain
problem without this basic knowledge.
A basic understanding of hand tools is necessary to
effectively use this section of the Service Manual.
ON-BOARD DIAGNOSTIC (OBD)
On-Board Diagnostic (Self Diagnosis
System) Tests
A diagnostic test is a series of steps, the result of which
is a pass or fail reported to the diagnostic ex ecutive.
When a diagnostic test reports a pass result, the
diagnostic ex ecutive records the following data:
The diagnostic test has been completed since the
last ignition cycle.
The diagnostic test has passed during the current
ignition cycle.
The fault identified by the diagnostic test is not
currently active.
When a diagnostic test reports a fail result, the
diagnostic ex ecutive records the following data:
The diagnostic test has been completed since the
last ignition cycle.
The fault identified by the diagnostic test is currently
active.
The fault has been active during this ignition cycle.
The operating conditions at the time of the failure.
The Diagnostic Executive
The Diagnostic Executive is a unique segment of
software which is designed to coordinate and prioritize
the diagnostic procedures as well as define the protocol
for recording and displaying their results. The main
responsibilities of the Diagnostic Ex ecutive are listed as
follow s:
Commanding the check engine lamp on and off
DTC logging and clearing
Current status information on each diagnostic
Diagnostic Information
The diagnostic charts and functional checks are
designed to locate a faulty circuit or component through
a process of logical decisions. The charts are prepared
with the requirement that the vehicle functioned
correctly at the time of assembly and that there are not
multiple faults present.
There is a continuous self-diagnosis on certain control
functions. This diagnostic capability is complemented
by the diagnostic procedures contained in this manual.
The language of communicating the source of the
malfunction is a system of diagnostic trouble codes.
When a malfunction is detected by the control module, a
diagnostic trouble code is set and the check engine
lamp is illuminated.
Check Engine Lamp
The check engine lamp looks the same as the check
engine lamp you are already familiar with, the “Check
Engine” lamp.
Basically, the check engine lamp is turned on when the

4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS 6E–361
SYMPTOM DIAGNOSIS
PRELIMINARY CHECKS
Before using this section, perform the “On-Board
Diagnostic (OBD) System Check” and verify all of the
following items:
The engine control module (ECM) and check engine
lamp (MIL=malfunction indicator lamp are operating
correctly.
There are no Diagnostic Trouble Code(s) stored.
Tech 2 data is within normal operating range. Refer to
Typical Scan Data Values.
Verify the customer complaint and locate the correct
symptom in the table of contents. Perform the
procedure included in the symptom chart.
VISUAL/PHYSICAL CHECK
Several of the symptom procedures call for a careful
visual/physical check. This can lead to correcting a
problem without further checks and can save valuable
time. This check should include the following items:
ECM grounds for cleanliness, tightness and proper
location.
Vacuum hoses for splits, kinks, and proper
connection. Check thoroughly for any type of leak or
restriction.
Air intake ducts for collapsed or damaged areas.
Air leaks at throttle body mounting area, mass air flow
(MAF) sensor and intake manifold sealing surfaces.
Wiring for proper connections, pinches and cuts.
INTERMITTENT
Important: An intermittent problem may or may not turn
on the check engine lamp (MIL=malfunction indicator
lamp) or store a Diagnostic Trouble Code. Do NOT use
the Diagnostic Trouble Code (DTC) charts for
intermittent problems.
The fault must be present to locate the problem.
Most intermittent problems are cased by faulty electrical
connections or wiring. Perform a careful visual/physical
check for the following conditions.
Poor mating of the connector halves or a terminal not
fully seated in the connector (backed out).
Improperly formed or damaged terminal.
All connector terminals in the problem circuit should
be carefully checked for proper contact tension.
Poor terminal-to-wire connection. This requires
removing the terminal form the connector body to
check.
Check engine lamp (MIL=malfunction indicator lamp)
wire to ECM shorted to ground.
Poor ECM grounds. Refer to the ECM wiring
diagrams.Road test the vehicle with a Digital Multimeter
connected to a suspected circuit. An abnormal voltage
when the malfunction occurs is a good indication that
there is a fault in the circuit being monitored.
Using Tech 2 to help detect intermittent conditions. The
Tech 2 have several features that can be used to
located an intermittent condition. Use the following
features to find intermittent faults:
To check for loss of diagnostic code memory,
disconnect the MAF sensor and idle the engine until the
check engine lamp (MIL=malfunction indicator lamp)
comes on. Diagnostic Trouble Code P0100 should be
stored and kept in memory when the ignition is turned
OFF.
If not, the ECM is faulty. When this test is completed,
make sure that you clear the Diagnostic Trouble Code
P0100 from memory.
An intermittent check engine lamp (MIL=malfunction
indicator lamp) with no stored Diagnostic Trouble Code
may be caused by the following:
Check engine lamp (MIL=malfunction indicator lamp)
wire to ECM short to ground.
Poor ECM grounds. Refer to the ECM wiring
diagrams.
Check for improper installation of electrical options such
as light, cellular phones, etc. Check all wires from ECM
to the ignition control module for poor connections.
Check for an open diode across the A/C compressor
clutch and check for other open diodes (refer to wiring
diagrams in Electrical Diagnosis).
If problem has not been found, refer to ECM connector
symptom tables.
Check the “Broadcast Code” of the ECM, and
compare it with the latest Isuzu service bulletins and/
or Isuzu EEPROM reprogramming equipment to
determine if an update to the ECM's reprogrammable
memory has been released.
This identifies the contents of the reprogrammable
software and calibration contained in the ECM.
If the “Broadcast Code” is not the most current
available, it is advisable to reprogram the ECM's
EEPROM memory, which may either help identify a
hard-to find problem or may fix the problem.
The Service Programming System (SPS) will not allow
incorrect software programming or incorrect calibration
changes.

6E-66 3.5L ENGINE DRIVEABILITY AND EMISSIONS
 Does it rely on some mechanical/vacuum
device to operate?

Physical:
 Where are the circuit components (componen
t
locators and wire harness routing diagrams):

Are there areas where wires could be
chafed or pinched (brackets or frames)?

Are there areas subjected to extreme
temperatures?

Are there areas subjected to vibration or
movement (engine, transmission or
suspension)?

Are there areas exposed to moisture, road
salt or other corrosives (battery acid, oil o
r
other fluids)?

Are there common mounting areas with
other systems/components?
 Have previous repairs been performed to
wiring, connectors, components or mounting
areas (causing pinched wires between panels
and drivetrain or suspension components
without causing and immediate problem)?
 Does the vehicle have aftermarket or dealer-
installed equipment (radios, telephone, etc.)

Step 2: Isolate the problem
At this point, you should have a good idea of what could
cause the present condition, as well as could not cause
the condition. Actions to take include the following:

Divide (and separate, where possible) the system
or circuit into smaller sections

Confine the problem to a smaller area of the
vehicle (start with main harness connections while
removing panels and trim as necessary in order to
eliminate large vehicle sections from furthe
r
investigation)

For two or more circuits that do not share a
common power or ground, concentrate on areas
where harnesses are routed together o
r
connectors are shared (refer to the following hints)

Hints
Though the symptoms may vary, basic electrical failures
are generally caused by:

Loose connections:
 Open/high resistance in terminals, splices,
connectors or grounds

Incorrect connector/harness routing (usually in
new vehicles or after a repair has been made):

 Open/high resistance in terminals, splices,
connectors of grounds

Corrosion and wire damage:
 Open/high resistance in terminals, splices,
connectors of grounds

Component failure:
 Opens/short and high resistance in relays,
modules, switches or loads


Aftermarket equipment affecting normal operation
of other systems You may isolate circuits by:

Unplugging connectors or removing a fuse to
separate one part of the circuit from another part

Operating shared circuits and eliminating those
that function normally from the suspect circuit

If only one component fails to operate, begin
testing at the component

If a number of components do no operate, begin
tests at the area of commonality (such as powe
r
sources, ground circuits, switches or majo
r
connectors)
What resources you should use
Whenever appropriate, you should use the following
resources to assist in the diagnostic process:

Service manual

Technical equipment (for data analysis)

Experience

Technical Assistance

Circuit testing tools
5d. Intermittent Diagnosis
By definition, an intermittent problem is one that does
not occur continuously and will occur when certain
conditions are met. All these conditions, however, may
not be obvious or currently known. Generally,
intermittents are caused by:

Faulty electrical connections and wiring

Malfunctioning components (such as sticking
relays, solenoids, etc.)

EMI/RFI (Electromagnetic/radio frequency
interference)

Aftermarket equipment
Intermittent diagnosis requires careful analysis of
suspected systems to help prevent replacing good
parts. This may involve using creativity and ingenuity to
interpret customer complaints and simulating all
external and internal system conditions to duplicate the
problem.

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-69
GENERAL SERVICE INFORMATION
Aftermarket Electrical and Vacuum
Equipment
Aftermarket (add-on) electrical and vacuum equipment
is defined as any equipment which connects to the
vehicle's electrical or vacuum systems that is installed
on a vehicle after it leaves the factory. No allowances
have been made in the vehicle design for this type o
f
equipment.
NOTE: No add-on vacuum equipment should be
added to this vehicle.
NOTE: Add-on electrical equipment must only be
connected to the vehicle's electrical system at the
battery (power and ground).
Add-on electrical equipment, even when installed to
these guidelines, may still cause the powertrain system
to malfunction. This may also include equipment no
t
connected to the vehicle electrical system such as
portable telephones and radios. Therefore, the firs
t
step in diagnosing any powertrain problem is to
eliminate all aftermarket electrical equipment from the
vehicle. After this is done, if the problem still exists, i
t
may be diagnosed in the normal manner.
Electrostatic Discharge Damage
Electronic components used in the ECM are often
designed to carry very low voltage. Electronic
components are susceptible to damage caused by
electrostatic discharge. Less than 100 volts of static
electricity can cause damage to some electronic
components. By comparison, it takes as much as 4000
volts for a person to feel even the zap of a static
discharge.




TS23793
There are several ways for a person to become
statically charged. The most common methods o
f
charging are by friction and induction.


An example of charging by friction is a person sliding
across a vehicle seat.

Charge by induction occurs when a person with well
insulated shoes stands near a highly charged objec
t
and momentary touches ground. Charges of the
same polarity are drained off leaving the person
highly charged with the opposite polarity. Static
charges can cause damage, therefore it is importan
t
to use care when handling and testing electronic
components.
NOTE: To prevent possible electrostatic discharge
damage, follow these guidelines:

Do not touch the ECM connector pins or soldered
components on the ECM circuit board.

Do not open the replacement part package until
the part is ready to be installed.

Before removing the part from the package,
ground the package to a known good ground on
the vehicle.

If the part has been handled while sliding across
the seat, while sitting down from a standing
position, or while walking a distance, touch a
known good ground before installing the part.

6E-70 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Fuel Quality
Fuel quality is not a new issue for the automotive
industry, but its potential for turning on the MIL (“Check
Engine" lamp) with OBD systems is new.
Fuel additives such as “dry gas" and “octane
enhancers" may affect the performance of the fuel. The
Reed Vapor Pressure of the fuel can also create
problems in the fuel system, especially during the spring
and fall months when severe ambient temperature
swings occur. A high Reed Vapor Pressure could sho
w
up as a Fuel Trim DTC due to excessive canister
loading. High vapor pressures generated in the fuel
tank can also affect the Evaporative Emission
diagnostic as well.
Using fuel with the wrong octane rating for your vehicle
may cause driveability problems. Many of the majo
r
fuel companies advertise that using “premium" gasoline
will improve the performance of your vehicle. Mos
t
premium fuels use alcohol to increase the octane rating
of the fuel. Although alcohol-enhanced fuels may raise
the octane rating, the fuel's ability to turn into vapor in
cold temperatures deteriorates. This may affect the
starting ability and cold driveability of the engine.
Low fuel levels can lead to fuel starvation, lean engine
operation, and eventually engine misfire.
Non-OEM Parts
All of the OBD diagnostics have been calibrated to run
with OEM parts.
Aftermarket electronics, such as cellular phones,
stereos, and anti-theft devices, may radiate EMI into the
control system if they are improperly installed. This may
cause a false sensor reading and turn on the MIL
(“Check Engine" lamp).
Environment
Temporary environmental conditions, such as localized
flooding, will have an effect on the vehicle ignition
system. If the ignition system is rain-soaked, it can
temporarily cause engine misfire and turn on the MIL
(“Check Engine" lamp).
Vehicle Marshaling
The transportation of new vehicles from the assembly
plant to the dealership can involve as many as 60 key
cycles within 5Km miles of driving. This type o
f
operation contributes to the fuel fouling of the spark
plugs and will turn on the MIL (“Check Engine" lamp).

Poor Vehicle Maintenance
The sensitivity of OBD diagnostics will cause the MIL
(“Check Engine" lamp) to turn on if the vehicle is no
t
maintained properly. Restricted air filters, fuel filters,
and crankcase deposits due to lack of oil changes o
r
improper oil viscosity can trigger actual vehicle faults
that were not previously monitored prior to OBD. Poo
r
vehicle maintenance can not be classified as a
“non-vehicle fault", but with the sensitivity of OBD
diagnostics, vehicle maintenance schedules must be
more closely followed.
Severe Vibration
The Misfire diagnostic measures small changes in the
rotational speed of the crankshaft. Severe driveline
vibrations in the vehicle, such as caused by an
excessive amount of mud on the wheels, can have the
same effect on crankshaft speed as misfire.
Related System Faults
Many of the OBD system diagnostics will not run if the
ECM detects a fault on a related system or component.
One example would be that if the ECM detected a
Misfire fault, the diagnostics on the catalytic converte
r
would be suspended until Misfire fault was repaired. If
the Misfire fault was severe enough, the catalytic
converter could be damaged due to overheating and
would never set a Catalyst DTC until the Misfire faul
t
was repaired and the Catalyst diagnostic was allowed to
run to completion. If this happens, the customer may
have to make two trips to the dealership in order to
repair the vehicle.
Maintenance Schedule
Refer to the Maintenance Schedule.
Visual/Physical Engine Compartment
Inspection
Perform a careful visual and physical engine
compartment inspection when performing any
diagnostic procedure or diagnosing the cause of an
emission test failure. This can often lead to repairing a
problem without further steps. Use the following
guidelines when performing a visual/physical inspection:

Inspect all vacuum hoses for punches, cuts,
disconnects, and correct routing.

Inspect hoses that are difficult to see behind othe
r
components.

Inspect all wires in the engine compartment fo
r
proper connections, burned or chafed spots, pinched
wires, contact with sharp edges or contact with ho
t
exhaust manifolds or pipes.

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-329
SYMPTOM DIAGNOSIS
PRELIMINARY CHECKS
Before using this section, perform the "On-Board
Diagnostic (OBD) System Check" and verify all of the
following items:

The engine control module (ECM) and check engine
lamp (MIL=malfunction indicator lamp) are operating
correctly.

There are no Diagnostic Trouble Code(s) stored.

Tech 2 data is within normal operating range. Refer
to Typical Scan Data Values.

Verify the customer complaint and locate the correct
symptom in the table of contents. Perform the
procedure included in the symptom chart.

VISUAL/PHYSICAL CHECK
Several of the symptom procedures call for a careful
visual/physical check. This can lead to correcting a
problem without further checks and can save valuable
time. This check should include the following items:

ECM grounds for cleanliness, tightness and proper
location.

Vacuum hoses for splits, kinks, and proper
connection. Check thoroughly for any type of leak or
restriction.

Air intake ducts for collapsed or damaged areas.

Air leaks at throttle body mounting area, manifold
absolute pressure (MAP) sensor and intake manifold
sealing surfaces.

Ignition wires for cracking, harness, and carbon
tracking.

Wiring for proper connections, pinches and cuts.

INTERMITTENT
Important: An intermittent problem may or may not turn
on the check engine lamp (MIL=malfunction indicato
r
lamp) or store a Diagnostic Trouble Code. Do NOT use
the Diagnostic Trouble Code (DTC) charts fo
r
intermittent problems.
The fault must be present to locate the problem.
Most intermittent problems are cased by faulty electrical
connections or wiring. Perform a careful visual/physical
check for the following conditions.

Poor mating of the connector halves or a terminal
not fully seated in the connector (backed out).

Improperly formed or damaged terminal.


All connector terminals in the problem circuit should
be carefully checked for proper contact tension.

Poor terminal-to-wire connection. This requires
removing the terminal form the connector body to
check.

Ignition coils shorted to ground and arcing at ignition
wires or plugs.

Check engine lamp (MIL=malfunction indicator lamp)
wire to ECM shorted to ground.

Poor ECM grounds. Refer to the ECM wiring
diagrams.

Road test the vehicle with a Digital Multimete
r
connected to a suspected circuit. An abnormal voltage
when the malfunction occurs is a good indication tha
t
there is a fault in the circuit being monitored.
Using Tech 2 to help detect intermittent conditions. The
Tech 2 have several features that can be used to
located an intermittent condition. Use the following
features to find intermittent faults:
To check for loss of diagnostic code memory,
disconnect the mass air flow (MAF) sensor and idle the
engine until the check engine lamp (MIL=malfunction
indicator lamp) comes on. Diagnostic Trouble Code
P0102 should be stored and kept in memory when the
ignition is turned OFF.
If not, the ECM is faulty. When this test is completed,
make sure that you clear the Diagnostic Trouble Code
P0102 from memory.

An intermittent check engine lamp (MIL=malfunction
indicator lamp) with no stored Diagnostic Trouble Code
may be caused by the following:

Ignition coil shorted to ground and arcing at ignition
wires or plugs.

Check engine lamp (MIL=malfunction indicator lamp)
wire to ECM short to ground.

Poor ECM grounds. Refer to the ECM wiring
diagrams.

Check for improper installation of electrical options such
as light, cellular phones, etc. Check all wires from ECM
to the ignition control module for poor connections.
Check for an open diode across the A/C compresso
r
clutch and check for other open diodes (refer to wiring
diagrams in Electrical Diagnosis).

6E–64 ENGINE DRIVEABILITY AND EMISSIONS
–Are there areas subjected to vibration or
movement (engine, transmission or
suspension)?
–Are there areas ex posed to moisture, road salt
or other corrosives (battery acid, oil or other
fluids)?
–Are there common mounting areas with other
systems/components?
–Have previous repairs been performed to wiring,
connectors, components or mounting areas
(causing pinched wires between panels and
drivetrain or suspension components without
causing and immediate problem)?
–Does the vehicle have aftermarket or dealer-
installed equipment (radios, telephone, etc.)
Step 2: Isolate the problem
At this point, you should have a good idea of what could
cause the present condition, as well as could not cause
the condition. Actions to take include the following:
Divide (and separate, where possible) the system or
circuit into smaller sections
Confine the problem to a smaller area of the vehicle
(start with main harness connections while removing
panels and trim as necessary in order to eliminate
large vehicle sections from further investigation)
For two or more circuits that do not share a common
power or ground, concentrate on areas where
harnesses are routed together or connectors are
shared (refer to the following hints)
Hints
Though the symptoms may vary, basic electrical failures
are generally caused by:
Loose connections:
–Open/high resistance in terminals, splices,
connectors or grounds
Incorrect connector/harness routing (usually in new
vehicles or after a repair has been made):
–Open/high resistance in terminals, splices,
connectors of grounds
Corrosion and wire damage:
–Open/high resistance in terminals, splices,
connectors of grounds
Component failure:
–Opens/short and high resistance in relays,
modules, switches or loads
Aftermarket equipment affecting normal operation of
other systems
You may isolate circuits by:
Unplugging connectors or removing a fuse to
separate one part of the circuit from another part
Operating shared circuits and eliminating those that
function normally from the suspect circuit
If only one component fails to operate, begin testingat the component
If a number of components do no operate, begin tests
at the area of commonality (such as power sources,
ground circuits, switches or major connectors)
What resources you should use
Whenever appropriate, you should use the following
resources to assist in the diagnostic process:
Service manual
Technical equipment (for data analysis)
Ex perience
Technical Assistance
Circuit testing tools
5d. Intermittent Diagnosis
By definition, an intermittent problem is one that does
not occur continuously and will occur when certain
conditions are met. All these conditions, however, may
not be obvious or currently known. Generally,
intermittents are caused by:
Faulty electrical connections and wiring
Malfunctioning components (such as sticking relays,
solenoids, etc.)
EMI/RFI (Electromagnetic/radio frequency
interference)
Aftermarket equipment
Intermittent diagnosis requires careful analysis of
suspected systems to help prevent replacing good
parts. This may involve using creativity and ingenuity to
interpret customer complaints and simulating all
ex ternal and internal system conditions to duplicate the
problem.
What you should do
Step 1: A cquire information
A thorough and comprehensive customer check sheet
is critical to intermittent problem diagnosis. You should
require this, since it will dictate the diagnostic starting
point. The vehicle service history file is another
source for accumulating information about the
complaint.
Step 2: A nalyze the intermittent problem
Analyze the customer check sheet and service history
file to determine conditions relevant to the suspect
system(s).
Using service manual information, you must identify,
trace and locate all electrical circuits related to the
malfunctioning system(s). If there is more than one
system failure, you should identify, trace and locate
areas of commonality shared by the suspect circuits.

ENGINE DRIVEABILITY AND EMISSIONS 6E–67
GENERAL SERVICE INFORMATION
Aftermarket Electrical and Vacuum
Equipment
Aftermarket (add-on) electrical and vacuum equipment
is defined as any equipment which connects to the
vehicle's electrical or vacuum systems that is installed
on a vehicle after it leaves the factory. No allowances
have been made in the vehicle design for this type of
equipment.
NOTE: No add-on vacuum equipment should be added
to this vehicle.
NOTE: Add-on electrical equipment must only be
connected to the vehicle's electrical system at the
battery (power and ground).
Add-on electrical equipment, even when installed to
these guidelines, may still cause the electric system to
malfunction. This may also include equipment not
connected to the vehicle electrical system such as
portable telephones and radios. Therefore, the first step
in diagnosing any electric problem is to eliminate all
aftermarket electrical equipment from the vehicle. After
this is done, if the problem still ex ists, it may be
diagnosed in the normal manner.
Electrostatic Discharge Damage
Electronic components used in the ECM are often
designed to carry very low voltage. Electronic
components are susceptible to damage caused by
electrostatic discharge. Less than 100 volts of static
electricity can cause damage to some electronic
components. By comparison, it takes as much as 4000
volts for a person to feel even the zap of a static
discharge.
There are several ways for a person to become
statically charged. The most common methods of
charging are by friction and induction.
An ex ample of charging by friction is a person sliding
across a vehicle seat.
Charge by induction occurs when a person with well-
insulated shoes stands near a highly charged object
and momentarily touches ground. Charges of the
same polarity are drained off leaving the person
highly charged with the opposite polarity. Static
charges can cause damage, therefore it is important
to use care when handling and testing electronic
components.Non-OEM Parts
All of the OBD diagnostics have been calibrated to run
with OEM parts. Accordingly, if commercially sold
sensor or switch is installed, it makes a wrong diagnosis
and turns on the check engine lamp.
Aftermarket electronics, such as cellular phones,
stereos, and anti-theft devices, may radiate EMI into the
control system if they are improperly installed. This may
cause a false sensor reading and turn on the check
engine lamp.
Poor Vehicle Maintenance
The sensitivity of OBD diagnostics will cause the check
engine lamp to turn on if the vehicle is not maintained
properly. Restricted oil filters, fuel filters, and crankcase
deposits due to lack of oil changes or improper oil
viscosity can trigger actual vehicle faults that were not
previously monitored prior to OBD. Poor vehicle
maintenance can not be classified as a “non-vehicle
fault”, but with the sensitivity of OBD diagnostics,
vehicle maintenance schedules must be more closely
follow ed.
Related System Faults
Many of the OBD system diagnostics will not run if the
ECM detects a fault on a related system or component.
Visual/Physical Engine Compartment
Inspection
Perform a careful visual and physical engine
compartment inspection when performing any
diagnostic procedure or diagnosing the cause of an
emission test failure. This can often lead to repairing a
problem without further steps. Use the following
guidelines when performing a visual/physical
inspection:
Inspect all vacuum hoses for punches, cuts,
disconnects, and correct routing.
Inspect hoses that are difficult to see behind other
components.
Inspect all wires in the engine compartment for
proper connections, burned or chafed spots, pinched
wires, contact with sharp edges or contact with hot
exhaust manifolds or pipes.
Basic Knowledge of Tools Required
NOTE: Lack of basic knowledge of this powertrain
when performing diagnostic procedures could result in
an incorrect diagnosis or damage to powertrain
components. Do not attempt to diagnose a powertrain
problem without this basic knowledge.
A basic understanding of hand tools is necessary to
effectively use this section of the Service Manual.