section list ISUZU TF SERIES 2004 Workshop Manual

ACCESSORIES 9-1

SECTION 9
ACCESSORIES
TABLE OF CONTENTS
PAGE
Parts Location ................................................................................................................... 9-2
Circuit Diagram ................................................................................................................. 9-6
Connector List .................................................................................................................. 9-10
Radio .................................................................................................................................. 9-12
Front Speaker .................................................................................................................... 9-13
Tweeter .............................................................................................................................. 9-14
Rear Speaker (Extend Cab)............................................................................................... 9-15
Rear Speaker (Crew Cab) .................................................................................................. 9-16
Clock ................................................................................................................................... 9-17
Antenna ............................................................................................................................. 9-18

9A-12 SUPPLEMENTAL RESTRAINT SYSTEM

Diagnosis
WARNING: TO AVOID DEPLOYMENT WHEN
TROUBLESHOOTING THE SRS, DO NOT USE
ELECTRICAL TEST EQUIPMENT SUCH AS A
BATTERY–POWERED OR AC–POWERED
VOLTMETER, OHMMETER, ETC., OR ANY TYPE
OF ELECTRICAL EQUIPMENT OTHER THAN THAT
SPECIFIED IN THIS MANUAL. DO NOT USE A
NONPOWERED PROBE–TYPE TESTER.
INSTRUCTIONS IN THIS MANUAL MUST BE
FOLLOWED CAREFULLY, OTHERWISE
PERSONAL INJURY MAY RESULT.
Diagnostic Trouble Codes
The “SRS Diagnostic System Check” must always be
the starting point of any SRS diagnosis. The “SRS
Diagnostic System Check” checks for proper “AIR
BAG” warning lamp operation and checks for SRS
diagnostic trouble codes using the scan tool.
1. Current diagnostic trouble codes – Malfunctions
that are presently being detected. Curren
t
diagnostic trouble codes are stored in RAM
(Random Access Memory).
2. History diagnostic trouble codes – All malfunctions
detected since the last time the history memor
y
was cleared. History diagnostic trouble codes are
stored in EEPROM.


Scan Tool Diagnostics
A scan tool is used to read current and history
diagnostic trouble codes and to clear all diagnostic
trouble codes after a repair is completed. The scan
tool must be updated to communicate with the SRS
through a replaceable cartridge before it can be used
for SRS diagnostics. To use the scan tool, connect it
to the data link connector and turn the ignition switch
“ON”. The scan tool reads serial data from the SRS
control unit “Serial Data” line terminal “21” to the data
link connector terminal “2”.

Use Of Special Tools
WARNING: TO AVOID DEPLOYMENT WHEN
TROUBLESHOOTING THE SRS, DO NOT USE
ELECTRICAL TEST EQUIPMENT SUCH AS A
BATTERY–POWERED OR AC–POWERED
VOLTMETER, OHMMETER, ETC, OR ANY TYPE OF
ELECTRICAL EQUIPMENT OTHER THAN THAT
SPECIFIED IN THIS MANUAL. DO NOT USE A NON
POWERED PROBE–TYPE TESTER.
INSTRUCTIONS IN THIS MANUAL MUST BE
FOLLOWED CAREFULLY, OTHERWISE
PERSONAL INJURY MAY RESULT. YOU SHOULD
BE FAMILIAR WITH THE TOOLS LISTED IN THIS
SECTION UNDER THE HANDLING SRS SPECIAL
TOOLS.
You should be able to measure voltage and
resistance. You should be familiar with proper use of
a scan tool such as the Tech 2 Diagnostic Computer,
SRS Driver/Passenger Load Tool 5-8840-2421-0,
Connector Test Adapter Kit 5-8840-0385-0 and the
DVM (Digital Multimeter) 5-8840-0285-0.

SUPPLEMENTAL RESTRAINT SYSTEM 9A-17

Air Bag Assembly Scrapping Procedure
During the course of a vehicle's useful life, certain
situations may arise which will necessitate the disposal
of a live (undeployed) air bag assembly. This
information covers proper procedures for disposing of
a live air bag assembly.
Before a live air bag assembly can be disposed of, it
must be deployed. A live air bag assembly must not
be disposed of through normal refuse channels.
WARNING: FAILURE TO FOLLOW PROPE
R
SUPPLEMENTAL RESTRAINT SYSTEM (SRS) AIR
BAG ASSEMBLY DISPOSAL PROCEDURES CAN
RESULT IN AIR BAG DEPLOYMENT WHICH MAY
CAUSE PERSONAL INJURY. AN UNDEPLOYED
AIR BAG ASSEMBLY MUST NOT BE DISPOSED
OF THROUGH NORMAL REFUSE CHANNELS.
THE UNDEPLOYED AIR BAG ASSEMBLY
CONTAINS SUBSTANCES THAT CAN CAUSE
SEVERE ILLNESS OR PERSONAL INJURY IF THE
SEALED CONTAINER IS DAMAGED DURING
DISPOSAL. DISPOSAL IN ANY MANNE
R
INCONSISTENT WITH PROPER PROCEDURES
MAY BE A VIOLATION OF FEDERAL, STATE, AND
/
OR LOCAL LAW.
In situations which require deployment of a live air bag
assembly, deployment may be accomplished inside or
outside the vehicle. The method employed depends
upon the final disposition of the particular vehicle, as
noted in “Deployment Outside Vehicle” and
“Deployment Inside Vehicle” in this section.

Deployment Outside Vehicle (Driver Air
Bag Assembly)
Deployment outside the vehicle is proper when the
vehicle is to be returned to service. This includes, for
example, situations in which the vehicle will be
returned to useful service after a functionally or
cosmetically deficient air bag assembly is replaced.
Deployment and disposal of a malfunctioning air bag
assembly is, of course, subject to any required
retention period.
For deployment of a live (undeployed) air bag
assembly outside the vehicle, the deployment
procedure must be followed exactly. Always wear
safety glasses during this deployment procedure until
a deployed air bag assembly is scrapped or until an
undeployed air bag assembly is shipped. Before
performing the procedures you should be familiar with
servicing the SRS and with proper handling of the air
bag assembly. Procedures should be read fully
before they are performed.
The following procedure requires use of 5-8840-2468-
06 SRS deployment harness with appropriate pigtail
adapter. Do not attempt procedure without 5-8840-
2468-0 adapter. WARNING: FAILURE TO FOLLOW PROCEDURES
IN THE ORDER LISTED MAY RESULT IN
PERSONAL INJURY. NEVER CONNECT
DEPLOYMENT HARNESS TO ANY POWE
R
SOURCE BEFORE CONNECTING DEPLOYMENT
HARNESS TO THE DRIVER AIR BAG ASSEMBLY.
DEPLOYMENT HARNESS SHALL REMAIN
SHORTED AND NOT BE CONNECTED TO A
POWER SOURCE UNTIL THE AIR BAG IS TO BE
DEPLOYED. THE AIR BAG ASSEMBLY WILL
IMMEDIATELY DEPLOY THE AIR BAG WHEN A
POWER SOURCE IS CONNECTED TO IT. WEA
R
SAFETY GLASSES THROUGHOUT THIS ENTIRE
DEPLOYMENT AND DISPOSAL PROCEDURE.
NOTE: This information applies only to driver air bag
assembly. Refer to “Deployment Outside Vehicle
(Passenger Air Bag assembly)” in this section fo
r
information on passenger air bag assembly scrapping.
1. Turn ignition switch to “LOCK”, remove key and
put on safety glasses.
2. Inspect 5-8840-2468-0 SRS Deployment Harness
and appropriate pigtail adapter for damage. I
f
harness or pigtail adapter is damaged, discard and
obtain a replacement.
3. Short the two SRS deployment harness leads
together by fully seating one banana plug into the
other. SRS deployment harness shall remain
shorted and not be connected to a power source
until the air bag is to be deployed.
827RS004
4. Connect the appropriate pigtail adapter to the SRS
deployment harness.
5. Remove the driver air bag assembly from vehicle.
Refer to “Inflator Module Removal” in this manual.

9A-20 SUPPLEMENTAL RESTRAINT SYSTEM

26. Temporarily store the driver air bag assembly with
its trim cover facing up, away from the surface
upon which it rests.

Deployment Outside Vehicle (Passenger
Air Bag Assembly)
WARNING: FAILURE TO FOLLOW PROPER SRS
AIR BAG ASSEMBLY DISPOSAL PROCEDURES
CAN RESULT IN AIR BAG DEPLOYMENT WHICH
MAY CAUSE PERSONAL INJURY. UNDEPLOYED
AIR BAG ASSEMBLIES MUST NOT BE DISPOSED
OF THROUGH NORMAL REFUSE CHANNELS.
THE UNDEPLOYED AIR BAG ASSEMBLY
CONTAINS SUBSTANCES THAT CAN CAUSE
SEVERE ILLNESS OR PERSONAL INJURY IF THE
SEALED CONTAINER IS DAMAGED DURING
DISPOSAL. DISPOSAL IN ANY MANNE
R
INCONSISTENT WITH PROPER PROCEDURES
MAY BE A VIOLATION OF FEDERAL, STATE
AND/OR LOCAL LAWS.
Deployment out of the vehicle is proper when the
vehicle is to be returned to service. This includes, for
example, situations in which a functionally or
cosmetically deficient air bag assembly is replaced.
Deployment and disposal of an air bag assembly is, of
course, subject to any required retention period.
For deployment of a live air bag assembly out of the
vehicle, the deployment procedure must be followed
exactly. Always wear safety glasses during this
deployment procedure until the deployed air bag
assembly is scrapped. Before performing the
procedures, you should be familiar with servicing the
SRS system and with proper handling of the air bag
assembly. Procedures should be read fully before
they are performed.
The following procedure requires use of 5-8840-2468-
0 SRS Deployment Harness with the appropriate
pigtail adapter. The procedure also requires the use
of 5-8840-2420-0 Passenger Side SRS Module
Deployment Fixture. Do not attempt this procedure
without 5-8840-2468-0 and adapter, and 5-8840-2420-
0.
WARNING: FAILURE TO FOLLOW PROCEDURES
IN THE ORDER LISTED MAY RESULT IN
PERSONAL INJURY. NEVER CONNECT
DEPLOYMENT HARNESS TO ANY POWE
R
SOURCE BEFORE CONNECTING DEPLOYMENT
HARNESS TO THE AIR BAG ASSEMBLY.
DEPLOYMENT HARNESS SHALL REMAIN
SHORTED AND NOT BE CONNECTED TO A
POWER SOURCE UNTIL THE AIR BAG IS TO BE
DEPLOYED. THE AIR BAG ASSEMBLY WILL
IMMEDIATELY DEPLOY THE AIR BAG WHEN A
POWER SOURCE IS CONNECTED TO IT. WEA
R
SAFETY GLASSES THROUGHOUT THIS ENTIRE
DEPLOYMENT AND DISPOSAL PROCEDURE. NOTE: This information applies only to passenger ai
r
bag assembly. Information for disposing of a live
driver air bag assembly can be found in “Deployment
Outside Vehicle” (Driver Air Bag Assembly) in this
section.
1. Turn ignition switch to “LOCK” remove key, and
put on safety glasses.
2. Inspect 5-8840-2468-0 SRS Deployment Harness
and appropriate pigtail adapter for damage. I
f
harness or pigtail is damaged, discard and obtain
a replacement.
3. Short the two SRS Deployment Harness leads
together by fully seating one banana plug into the
other. The SRS Deployment Harness shall
remain shorted and not be connected to a powe
r
source until the air bag is to be deployed.
827RS003
4. Connect the appropriate pigtail adapter to the SRS
Deployment Harness
827RS004

SUPPLEMENTAL RESTRAINT SYSTEM 9A-27

Service Precautions for SRS
Component Service
CAUTION: When fasteners are removed, always
reinstall them at the same location from which
they were removed. If a fastener needs to be
replaced, use the correct part number fastener fo
r
that application. If the correct part number
fastener is not available, a fastener of equal size
and strength (or stronger) may be used. fasteners
that are not reused, and those requiring thread
locking compound will be called out. The correct
torque value must be used when installing
fasteners that require it. If the above conditions
are not followed, parts or system damage could
result.
WARNING: WHEN PERFORMING SERVICE ON O
R
AROUND SRS COMPONENTS OR SRS WIRING,
FOLLOW THE PROCEDURES LISTED BELOW TO
TEMPORARILY DISABLE THE SRS. FAILURE TO
FOLLOW PROCEDURES COULD RESULT IN
POSSIBLE AIR BAG DEPLOYMENT, PERSONAL
INJURY OR OTHERWISE UNNEEDED SRS
REPAIRS.
The SRS control unit in Driver–Passenger SRS can
maintain sufficient voltage to cause a deployment for
up to 15 seconds after the ignition switch is turned
“OFF,” the battery is disconnected, or the fuse
powering the SRS control unit is removed.
Many of the service procedures require removal of the
“SRS” fuse, and disconnection of the air bag assembly
from the deployment loop to avoid an accidental
deployment. If the air bag assembly is disconnected
from the deployment loop as noted in the “Disabling
the SRS” procedure that follows, service can begin
immediately without waiting for the 15 second time
period to expire.

Disabling The SRS
Removal
Turn the ignition switch to “OFF” and turn the steering
wheel so that the vehicle's wheels are pointing straight
ahead.
1. Remove SRS fuse “SRS” from left dash side lowe
r
fuse block or disconnect battery.
2. Disconnect yellow connector at the base o
f
steering column.
3. Remove glove box assembly; Refer to “Passenge
r
air bag assembly replacement” in this section.
4. Disconnect passenger air bag assembly yello
w
connector behind the glove box assembly.
CAUTION: With the “SRS” fuse removed and
ignition switch “ON,” the “AIR BAG” warning lamp
will be “ON.” This is normal operation and does
not indicate an SRS malfunction.
Enabling The SRS
Installation
Turn ignition switch to “LOCK” and remove key.
1. Connect yellow connector passenger air bag
assembly.
2. Install glove box assembly. Refer to “Passenge
r
Air Bag Assembly Replacement” in this section.
3. Connect yellow connector at the base of the
steering column.
4. Install “AIR BAG” fuse “SRS” to left dash side
lower fuse block or connect battery.
Turn ignition switch to “ON” and verify that the “AIR
BAG” warning lamp flashes seven times and then
turns “OFF.” If it does not operate as described,
perform the “SRS Diagnostic System Check” in this
section.

Handling / Installation / Diagnosis
1. Air bag assembly should not be subjected to
temperatures above 65

C (150

F).
2. Air bag assembly, and SRS control unit should not
be used if they have been dropped from a height
of 100 centimeters (3.28 feet) or more.
3. When a SRS control unit is replaced, it must be
oriented with the arrow on the SRS control unit
pointing toward the front of the vehicle. It is ver
y
important for the SRS control unit to be located flat
on the mounting surface, parallel to the vehicle
datum line. It is important that the SRS control unit
mounting surface is free of any dirt or other foreign
material.
4. Do not apply power to the SRS unless all
components are connected or a diagnostic chart
requests it, as this will set a diagnostic trouble
code.
5. The “SRS Diagnostic System Check” must be the
starting point of any SRS diagnostics. The “SRS
Diagnostic System Check” will verify proper “AIR
BAG” warning lamp operation and will lead you to
the correct chart to diagnose any SRS
malfunctions. Bypassing these procedures ma
y
result in extended diagnostic time, incorrect
diagnosis, and incorrect parts replacements.

Inspections Required After An Accident
CAUTION: Certain SRS components must be
replaced after a frontal crash involving air bag
deployment.
In all types of accidents regardless of “Air Bag”
deployment, visually inspect all of the following
components and replace as required:

RESTRAINT CONTROL 9A1-7

System Schematic


RTW49JLF000101

SRS Diagnostic System Check
The diagnostic procedures used in this section are
designed to find and repair SRS malfunctions. To get
the best results, it is important to use the diagnostic
charts and follow the sequence listed below:
A
Perform the “SRS Diagnostic System Check.”

The “SRS Diagnostic System Check” must be the
starting point of any SRS diagnostics. The “SRS
Diagnostic System Check” checks for proper “AIR
BAG” warning lamp operation, the ability of the SRS
control unit to communicate through the “Serial
Data” line and whether SRS diagnostic trouble codes
exist.

B
Refer to the proper diagnostic chart as directed by
the “SRS Diagnostic System Check.”

The “SRS Diagnostic System Check” will lead you to
the correct chart to diagnose any SRS malfunctions.
Bypassing these procedures may result in extended
diagnostic time, incorrect diagnosis and incorrect
parts replacement.
C
Repeat the “SRS Diagnostic System Check” after
any repair or diagnostic procedures have been
preformed.

Performing the “SRS Diagnostic System Check”
after all repair or diagnostic procedures will ensure
that the repair has been made correctly and that no
other malfunctions exist

BRAKE CONTROL SYSTEM 5A-1


SECTION 5A
BRAKE CONTROL SYSTEM
CONTENTS

Service Precaution ............................................................................................................. 5A-4
General Description ........................................................................................................... 5A-5
EHCU, Brake Pipe Diagram .......................................................................................... 5A-6
Hydraulic Unit (H/U)....................................................................................................... 5A-7
Normal Braking ......................................................................................................... 5A-8
Pressure Isolation (Pressure Maintain) .................................................................. 5A-9
Pressure Reduction .................................................................................................. 5A-10
Brake Release ........................................................................................................... 5A-11
Circuit Diagram.............................................................................................................. 5A-12
Connector List ............................................................................................................... 5A-13
Part Location ................................................................................................................. 5A-15
EHCU Pin-outs ............................................................................................................... 5A-17
System Components ..................................................................................................... 5A-19
Electronic Hydraulic Control Unit (EHCU) .............................................................. 5A-19
ABS Warning Lamp .................................................................................................. 5A-19
Wheel Speed Sensor (WSS)..................................................................................... 5A-19
G-Sensor ................................................................................................................... 5A-19
Normal and Anti-lock Braking ................................................................................. 5A-19
Electronic Brake-force Distribution (EBD) System ................................................ 5A-20
Brake Pedal Travel.................................................................................................... 5A-20
Acronyms and Abbreviations ....................................................................................... 5A-20
General Diagnosis ............................................................................................................. 5A-20
General Information ...................................................................................................... 5A-20
ABS Service Precautions.............................................................................................. 5A-20
Computer System Service Precautions....................................................................... 5A-21
General Service Precautions........................................................................................ 5A-21
Note on Intermittents .................................................................................................... 5A-21
Test Driving ABS Complaint Vehicles ......................................................................... 5A-21
"ABS and Brake" Warning Lamp ................................................................................. 5A-22
Normal Operation .......................................................................................................... 5A-22

ELECTRICAL-BODY AND CHASSIS 8A-1
SECTION 8A
ELECTRICAL-BODY AND CHASSIS
TABLE OF CONTENTS
PAGE
General Information ........................................................................................................ 8A- 4
Notes for Working on Electrical Items .......................................................................... 8A- 5
Symbols and Abbreviations ........................................................................................... 8A- 11
Symbols ...................................................................................................................... 8A- 11
Abbreviations ............................................................................................................. 8A- 12
Parts for Electrical Circuit .............................................................................................. 8A- 13
Wiring .......................................................................................................................... 8A- 13
Fuse ............................................................................................................................. 8A- 15
Fusible Link ................................................................................................................ 8A- 15
Relay ............................................................................................................................ 8A- 16
Diode ........................................................................................................................... 8A- 17
Connector ................................................................................................................... 8A- 18
Battery ......................................................................................................................... 8A- 19
Reading the Circuit Diagram .......................................................................................... 8A- 22
Parts Location ............................................................................................................ 8A- 22
Circuit Diagram ........................................................................................................... 8A- 23
Connector List ............................................................................................................. 8A- 23
Main Data and Specifications ........................................................................................ 8A- 24
Bulb Specifications .................................................................................................... 8A- 24
Relay and Fuse ................................................................................................................ 8A- 26
Relay and Fuse Box Location ................................................................................... 8A- 26
Relay Location ............................................................................................................ 8A- 28

4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS 6E–1
ENGINE
CONTENTS
4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS
ABBREVIATION CHARTS ........................ 6E-9
4JA1-TC .................................................... 6E-10
4JH1-TC .................................................... 6E-11
ECM CIRCUIT DIAGRAM (4JA1-TC) ........ 6E-14
ECM CIRCUIT DIAGRAM (4JA1-TC) ........ 6E-15
ECM CIRCUIT DIAGRAM (4JH1-TC) ........ 6E-16
ECM CIRCUIT DIAGRAM (4JH1-TC) ........ 6E-17
GROUND POINT CHART GENERAL EXPORT
(LHD) (1/4) ............................................... 6E-18
LOCATION ................................................ 6E-34
PARTS LOCATION ................................... 6E-39
CONNECTOR LIST ................................... 6E-40
RELAY AND FUSE .................................... 6E-43
RELAY AND FUSE BOX LOCATION
(LHD & RHD) ........................................... 6E-43
RELAY AND FUSE BOX LOCATION
(LHD & RHD) ........................................... 6E-44
FUSE AND RELAY LOCATION (LHD & RHD) 6E-45
ECM WIRING DIAGRAM (1/7) .................. 6E-46
ECM WIRING DIAGRAM (2/7) .................. 6E-47
ECM WIRING DIAGRAM (3/7) .................. 6E-48
ECM WIRING DIAGRAM (4/7) .................. 6E-49
ECM WIRING DIAGRAM (5/7) .................. 6E-50
ECM WIRING DIAGRAM (6/7) .................. 6E-51
ECM WIRING DIAGRAM (7/7) .................. 6E-52
ECM CONNECTOR PIN ASSIGNMENT &
OUTPUT SIGNAL .................................... 6E-53
GENERAL DESCRIPTION FOR ECM AND
SENSORS ............................................... 6E-64
Engine Control Module (ECM) ................... 6E-64
Pump Control Unit (PSG) & Data Ex change
Between Control Module ......................... 6E-64
Mass Air Flow (MAF) Sensor & Intake Air
Temperature (IAT) Sensor ....................... 6E-65
Throttle Position Sensor (TPS) .................. 6E-66
Crankshaft Position (CKP) Sensor ............ 6E-66
Engine Coolant Temperature (ECT) Sensor 6E-67
Vehicle Speed Sensor (VSS) .................... 6E-67
GENERAL DESCRIPTION FOR EGR
(EXHAUST GAS RE-CIRCULATION) ..... 6E-68
GENERAL DESCRIPTION FOR
INJECTION PUMP .................................. 6E-70Outline ....................................................... 6E-70
Cross-section View .................................... 6E-70
Low Pressure Fuel Circuit .......................... 6E-71
High Pressure Fuel Circuit ......................... 6E-72
Pump Camshaft Speed Sensor ................. 6E-72
High Pressure Solenoid Valve ................... 6E-73
Timing Control Valve (TCV) ....................... 6E-74
ISUZU Strategy Based Diagnostics .............. 6E-76
Overview .................................................... 6E-76
STRATEGY BASED DIAGNOSTICS CHART 6E-76
Diagnostic Thought Process ...................... 6E-77
1. Verify the Complaint .............................. 6E-77
2. Perform Preliminary Checks .................. 6E-77
3. Check Bulletins and Troubleshooting Hints 6E-78
4. Perform Service Manual Diagnostic Checks 6E-78
5a and 5b. Perform Service Manual Diagnostic
Procedures .............................................. 6E-78
5c. Technician Self Diagnoses .................. 6E-78
5d. Intermittent Diagnosis .......................... 6E-79
5e. Vehicle Operates as Designed ............ 6E-80
6. Re-examine the complaint ..................... 6E-81
7. Repair and Verify Fix ............................. 6E-81
GENERAL SERVICE INFORMATION ....... 6E-82
ON-BOARD DIAGNOSTIC (OBD) ............. 6E-82
TECH 2 OPERATING FLOW CART
(START UP) ............................................. 6E-86
TYPICAL SCAN DATA & DEFINITIONS
(ENGINE DATA) ................................... 6E-88
TYPICAL SCAN DATA & DEFINITIONS
(ENGINE DATA) ................................... 6E-90
MISCELLANEOUS TEST .......................... 6E-92
Plotting Snapshot Graph ............................ 6E-93
Plotting Graph Flow Chart (Plotting graph
after obtaining vehicle information) .......... 6E-94
Flow Chart for Snapshot Replay
(Plotting Graph) ....................................... 6E-95
SNAPSHOT DISPLAY WITH TIS2000 ...... 6E-96
ON-BOARD DIAGNOSTIC (OBD) SYSTEM
CHECK .................................................... 6E-105
Circuit Description ...................................... 6E-105
Diagnostic Aids .......................................... 6E-105
Test Description ......................................... 6E-105

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