electrical system ISUZU TROOPER 1998 Service Repair Manual

8DÐ14 WIRING SYSTEM
Fuse
Fuses are the most common form of circuit protection
used in vehicle wiring. A fuse is a thin piece of wire or strip
of metal encased in a glass or plastic housing. It is wired
in series with the circuit it protects. When there is an
overload of current in a circuit, such as a short of a ground,
the metal strip is designed to burn out and interrupt the
flow of current. This prevents a surge of high current from
reaching and damaging other components in the circuit.
Determine the cause of the overloaded before replacing
the fuse.
The replacement fuse must have the same amperage
specification as the original fuse.
Never replace a blown fuse with a fuse of a different
amperage specification.
Doing so can result in an electrical fire or other serious
circuit damage. A blown fuse is easily identified as shown
in the figure.

WIRING SYSTEM 8DÐ15
Fusible Link
The fusible link is primarily used to protect circuits where
high amounts of current flow and where it would not be
practical to use a fuse. For example, the starter circuit.
When a current overload occurs, the fusible link melts
open and interrupts the flow of current so as to prevent
the rest of the wiring harness from burning.
Determine the cause of the overload before replacing the
fusible link. the replacement fusible link must have the
same amperage specification as the original fusible link.
Never replace a blown fusible link with fusible link of a
different amperage specification. Doing so can result in
an electrical fire or other serious circuit damage.
A blown fusible link is easily identified as shown in the
figure.
Normal Blown
Fusible Link Specifications
Type Rating Case Color Maximum Circuit Current (A)
Connector 30A Pink 15
Connector 40A Green 20
Bolted 50A Red 25
Bolted 60A Yellow 30
Bolted 80A Black 40

8DÐ80 WIRING SYSTEM
Powertrain Control Module (PCM)
General Description
The Powertrain Control Module (PCM) is located in
the passenger compartment.
The PCM constantly monitors the information from
various sensors, and controls the systems that affect
vehicle performance.
The PCM performs the diagnostic function of the
system. It can recognize operational problems, alert
the driver through the Malfunction Indicator Light
(MIL) and store a Diagnostic Trouble Code (DTC) or
DTC(s) which identify the problem areas to aid the
technician in making repairs.
The PCM is designed to process the various input
informations and then sends the necessary
electrical responses to control fuel delivery, spark
timing and other emission control systems. The
input information has an interrelation to more than
one output, therefore, if the one input failed, it could
affect more than one system operation.
Refer to Driveability and Emission in Engine section
and Automatic Transmission in Transmission
section.

WIRING SYSTEM 8D – 543
Supplemental Restraint System (SRS) – Air Bag
General Description
The circuit consists of Sensing and Diagnostic Mod-
ule (SDM), driver’s air bag assembly, SRS coil assem-
bly, passenger’s air bag assembly, and “AIR BAG”
warning light. SDM, SRS coil assembly (driver side
only), driver air bag assembly, passenger air bag
assembly and connector wire make up the deploy-
ment loops. The function of the deployment loops is
to supply current through air bag assembly, which
will cause deployment of the air bags in the event of
a frontal crash of sufficient force, up to 30 degrees off
the center line of the vehicle. The air bag assemblies
are only supplied enough current to deploy when the
SDM detects vehicle velocity changes severe enough
to warrant deployment.
The SDM contains a sensing device which converts
vehicle velocity changes to an electrical signal.
The electrical signal generated is processed by the
SDM and then compared to a value stored in memory.
When the generated signal exceeds the stored value,
the SDM will cause current to flow through the air bag
assembly deploying the air bags.
Refer to Supplemental Restraint System in Restraints
section.

SUPPLEMENTAL RESTRAINT SYSTEM9J±3
System Description
The SRS consists of the Sensing and Diagnostic Module
(SDM), the driver air bag assembly, the SRS coil
assembly, the passenger air bag assembly and the ªAIR
BAGº warning lamp in the instrument cluster. The SDM,
SRS coil assembly (driver side only), driver air bag
assembly, passenger air bag assembly and connector
wire make up the deployment loops. The function of the
deployment loops is to supply current through air bag
assembly, which will cause deployment of the air bags in
the event of a frontal crash of sufficient force, up to 30degrees off the centerline of the vehicle. The air bag
assemblies are only supplied enough current to deploy
when the SDM detects vehicle velocity changes severe
enough to warrant deployment.
The SDM contains a sensing device which converts
vehicle velocity change to an electrical signal. The
electrical signal generated is processed by the SDM and
then compared to a value stored in memory. When the
generated signal exceeds the stored value, the SDM will
cause current to flow through the air bag assembly
deploying the air bags.
D09RW014

SUPPLEMENTAL RESTRAINT SYSTEM9J±5
1. Energy Reserve Ð The SDM maintains 24±Volt Loop
Reserve (24VLR) energy supply to provide
deployment energy when ignition voltage is lost in a
frontal crash.
2. Frontal Crash Detection Ð The SDM monitors
vehicle velocity changes to detect frontal crashes
which are severe enough to warrant deployment.
3. Air Bag Deployment Ð When a frontal crash of
sufficient force is detected, the SDM will cause
enough current to flow through the air bag assembly
to deploy the air bag.
4. Malfunction Detection Ð The SDM performs
diagnostic monitoring of SRS electrical components
and sets a diagnostic trouble code when a
malfunction is detected.
5. Frontal Crash Recording Ð The SDM records
information regarding SRS status during frontal
crash.
6. Malfunction Diagnosis Ð The SDM displays SRS
diagnostic trouble codes and system status
information through the use of a scan tool.
7. Driver Notification Ð The SDM warns the vehicle
driver of SRS malfunctions by controlling the ªAir
Bagº warning lamp.
The SDM is connected to the SRS wiring harness by a
24±pin connector. This harness connector uses a
shorting clip across certain terminals in the contact area.
This shorting clip connects the ªAIR BAGº warning lamp
to ground when the SDM harness connector is
disconnected or CPA (Connector Position Assurance) is
not inserted even if completely connected. This will
cause the ªAIR BAGº warning lamp to come ªONº steady
whenever the ignition switch is at the ON or START
positions with the SDM disconnected.
827RW044
Legend
(1) SDM
(2) SRS Harness
(3) Connector Position Assurance
ªAir Bagº Warning Lamp
Ignition voltage is applied to the ªAIR BAGº warning lamp
when the ignition switch is at the ON or START positions.
The SDM controls the lamp by providing ground with a
lamp driver. The ªAIR BAGº warning lamp is used in the
SRS to do the following:
1. Verify lamp and SDM operation by turn on 3.5
seconds and then turns ªOFFº when the ignition
switch is first turned ªONº.
2. Warn the vehicle driver of SRS electrical system
malfunctions which could potentially affect the
operation of the SRS. These malfunctions could
result in nondeployment in case of a frontal crash or
deployment for conditions less severe than intended.
The ªAIR BAG º warning lamp is the key to driver
notification of SRS malfunctions. For proper lamp
operation, refer to the ªSRS Diagnostic System Checkº in
this section.
821RW037
SRS Coil Assembly
The SRS coil assembly consists of two current carrying
coils. This is attached to the steering column and allow
rotation of the steering wheel while maintaining
continuous contact of the driver deployment loop to the
driver air bag assembly.
There is a shorting clip on the yellow 2±pin connector near
the base of steering column which connects the SRS coil
to the SRS wiring harness.
The shorting clip shorts to the SRS coil and driver air bag
assembly when the yellow 2±pin connector is
disconnected. The circuit to the driver air bag assembly is
shorted in this way to help prevent unwanted deployment
of the air bag when servicing the steering column or other
SRS components.

SUPPLEMENTAL RESTRAINT SYSTEM9J±7
Steering Column
The steering column absorbs energy and is designed to
compress in a frontal crash to decrease the chance of
injury to the driver.
431RW019
Knee Bolster
The knee bolsters are used to absorb energy to protect
knees and control the forward movement of the vehicle's
front seat occupants during a frontal crash, by limiting leg
movement.
740RT015
Definitions
Air Bag
An inflatable cloth cushion designed to deploy in certain
frontal crashes. It supplements the protection offered by
the seat belts by distributing the impact load more evenly
over the vehicle occupant's head and torso.
Asynchronous
Performed in a nonperiodic fashion, (i.e., no defined time
or interval).B+
Battery voltage, (B+) The voltage available at the battery
at the time of the indicated measurement. With the key
ªONº and the engine not running, the system voltage will
likely be between 12 and 12.5 volts. At idle, the voltage
may be 14 to 16 volts. The voltage could be as low as 10
volts during engine cranking.
Bulb Check
The SDM will cause the ªAIR BAGº warning lamp to turn
on 3.5 seconds and then go ªOFFº whenever the ignition
switch transitions to the ON position from any other
ignition switch position and no malfunctions are detected.
ªContinuous Monitoringº
Tests performed by the SDM on the SRS every 100
milliseconds while ªIgnition 1º voltage is in the normal
operating voltage range at the SDM.
Data Link Connector (DLC)
Formerly ªDLCº a connector which allows communication
with an external computer, such as a scan tool.
Datum Line
A base line parallel to the plane of the underbody or frame
from which all vertical measurements originate.
Deploy
To inflate the air bag.
Deployment Loops
The circuits which supply current to the air bag
assemblies to deploy the air bag.
Diagnostic Trouble Code (DTC)
Formerly ªCodeº, a numerical designator used by the
SDM to indicate specific SRS malfunctions.
Driver Current Source
An output of the SDM which applies current into the driver
air bag assembly circuit during the ªInitiator Assembly
Resistance Testº.
Driver Air Bag Assembly
An assembly located in the steering wheel hub consisting
of an inflatable bag, an inflator and an initiator.
EEPROM
Electrically Erasable Programmable Read Only Memory.
Memory which retains its contents when power is
removed from the SDM.
Ignition Cycle
The voltage at the SDM ªIgnition 1º inputs, with ignition
switch ªONº, is within the normal operating voltage range
for at least ten seconds before turning ignition switch
ªOFFº.
Ignition 1
A battery voltage (B+) circuit which is only powered with
the ignition switch in the ON, or START positions.
Initiator
The electrical component inside the air bag assembly
which, when sufficient current flows, sets off the chemical
reaction that inflates the air bag.
ªInitiator Assembly Resistance Testº
Tests performed once each ignition cycle when no
malfunctions are detected during ªTurn±ONº or
ªContinuous Monitoringº. This test checks for the correct
SDM configuration for the vehicle, shorts to ªIgnition 1º in

SUPPLEMENTAL RESTRAINT SYSTEM 9J±8
the deployment loops, high resistance or opens in the
ªDriver Side Highº, ªDriver Side Lowº, ªPassenger Side
Highº and ªPassenger Side Lowº circuits and measures
the resistance of the inflator assembly consisting of 1)
Initiators, 2) SRS coil assembly (driver side only), 3)
Connectors and associated wiring.
Normal Operating Voltage Range
The voltage measured between the SDM ªIgnition 1º
terminals and ªGroundº terminals is between 9 and 16
volts.
Passenger Current Source
An output of the SDM which applies current into the
passenger air bag assembly circuit during the ªInitiator
Assembly Resistance Testº.
Passenger Air Bag Assembly
An assembly located in the right side of the instrument
panel consisting of an inflatable bag, an inflator and an
initiator.
Scan Tool
An external computer used to read diagnostic information
from on±board computers via the data link connector.
SDM
Sensing and Diagnostic Module which provides reserve
energy to the deployment loops, deploys the air bags
when required and performs diagnostic monitoring of all
SRS components.
Serial Data
Information representing the status of the SRS.
SRS
Supplemental Restraint System.
SRS Coil Assembly
An assembly of two current±carrying coils in the driver
deployment loop that allows the rotation of the steering
wheel while maintaining the continuous contact of the
driver deployment loop to the driver air bag assembly.
SRS Wiring Harness
The wires and connectors that electrically connect the
components in the SRS.
ªTurn±ONº
Test which the SDM performs on the SRS once during
each ignition cycle immediately after ªIgnition 1º voltage
is applied to the SDM and before ªContinuous
Monitoringº.
Diagnosis
WARNING: T O AV O I D D E P L O Y M E N T W H E N
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 ªSRS Diagnostic System Checkº must always be the
starting point of any SRS diagnosis. The ªSRS
Diagnostic System Checkº checks for proper ªAIR BAGº
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. Current diagnostic
trouble codes are stored in RAM (Random Access
Memory).
2. History diagnostic trouble codes ± All malfunctions
detected since the last time the history memory 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 ªONº. The scan
tool reads serial data from the SDM ªSerial Dataº line
terminal ª24º to the data link connector terminal ª9º.
Use Of Special Tools
WARNING: T O AV O I D D E P L O Y M E N T W H E N
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 SYSTEM9J±21
THROUGHOUT THIS ENTIRE DEPLOYMENT AND
DISPOSAL PROCEDURE.
9. Twist together one connector wire lead to one
deployment wire. The connection should be
mechanically secure.
10. Bend twisted connection made in the previous step
flat and wrap tightly with electrical tape to insulate and
secure.
11. Twist together, bend and tape the remaining
connector wire lead to the remaining deployment
wire.
12. Connect the deployment harness to the driver air bag
assembly, yellow 2±pin connector at the base of the
steering column. Route deployment harness out the
driver side of the vehicle.
WARNING: DEPLOYMENT WIRES 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.
CONNECTING THE DEPLOYMENT WIRES TO THE
POWER SOURCE SHOULD ALWAYS BE THE FINAL
STEP IN THE AIR BAG ASSEMBLY DEPLOYMENT
PROCEDURE.
FAILURE TO FOLLOW PROCEDURES IN THE
ORDER LISTED COULD RESULT IN PERSONAL
INJURY.
13. Disconnect passenger air bag assembly, yellow 2±pin
connector located behind glove box assembly.
14. Cut the passenger air bag assembly harness
connector from the vehicle leaving at least 15 cm (six
inches) of wire at the connector.
15. Strip 13 mm (1/2 inch) of insulation from blue±white
and pink±blue wire lead of the connector.
16. Cut two 900 cm (30 feet) deployment wires from 0.8
mm
(18 gauge) or thicker multi±strand wire. These
wires will be used to fabricate the passenger
deployment harness.
17. Strip 13 mm (1/2 inch) of insulation from both ends of
the wires cut in the previous step.
18. Short the wires by twisting together one end from
each. Deployment wires shall remain shorted and not
be connected to a power source until the air bag is to
be deployed.
WARNING: FAILURE TO FOLLOW PROCEDURES IN
THE ORDER LISTED COULD RESULT IN PERSONAL
INJURY. NEVER CONNECT DEPLOYMENT WIRES
TO ANY POWER SOURCE BEFORE CONNECTING
DEPLOYMENT WIRES TO THE AIR BAG ASSEMBLY
LEADS. DEPLOYMENT WIRES 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. WEAR SAFETY GLASSES
THROUGHOUT THIS ENTIRE DEPLOYMENT AND
DISPOSAL PROCEDURE.19. Twist together one connector wire lead to one
deployment wire. The connection should be
mechanically secure.
20. Bend twisted connection made in the previous step
flat and wrap tightly with electrical tape to insulate and
secure.
21. Twist together, bend and tape the remaining
connector wire lead to the remaining deployment
wire.
22. Connect the deployment harness to the passenger air
bag assembly, yellow 2±pin connector located behind
the glove box assembly. Route deployment harness
out the passenger side of the vehicle.
WARNING: DEPLOYMENT WIRES 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. CONNECTING THE
DEPLOYMENT WIRES SHOULD ALWAYS BE THE
FINAL STEP IN THE AIR BAG ASSEMBLY
DEPLOYMENT PROCEDURE. FAILURE TO FOLLOW
PROCEDURES IN THE ORDER LISTED COULD
RESULT IN PERSONAL INJURY.
23. Verify that the inside of the vehicle and the area
surrounding the vehicle are clear of all people and
loose or flammable objects.
24. Stretch the driver and passenger deployment
harness to their full length.
25. Completely cover windshield area and front door
window openings with a drop cloth, blanket or similar
item. This reduces the possibility of injury due to
possible fragmentation of the vehicle's glass or
interior.
26. Notify all people in the immediate area that you intend
to deploy the air bags. The deployment will be
accompanied by a substantial noise which may
startle the uninformed.
27. Separate the two ends of the driver deployment
harness wires.
WARNING: DEPLOYMENT WIRES SHALL REMAIN
SHORTED AND NOT BE CONNECTED TO A POWER
SOURCE UNTIL THE AIR BAG IS 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. CONNECTING THE
DEPLOYMENT WIRES TO THE POWER SOURCE
SHOULD ALWAYS BE THE FINAL STEP IN THE AIR
BAG ASSEMBLY DEPLOYMENT PROCEDURE.
FAILURE TO FOLLOW PROCEDURES IN THE
ORDER LISTED COULD RESULT IN PERSONAL
INJURY.
NOTE: W h e n t h e a i r b a g deploys, the rapid gas
expansion will create a substantial noise. Notify all
people in the immediate area that you intend to deploy the
air bags.

SUPPLEMENTAL RESTRAINT SYSTEM 9J±26
Special Tools
WARNING: T O AV O I D D E P L O Y M E N T W H E N
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.
5±8840±2421±0 SRS Driver/Passenger
Load Tool
901RS146The SRS Driver/Passenger Load Tool 5±8840±2421±0 is
used only when called for in this section. It is used as a
diagnostic aid and safety device to prevent inadvertent air
bag assembly deployment.
The load tool has three yellow connectors attached to its
case.
The three small connectors are electrically functional and
serve as resistive load substitutions.
No more than two connectors are used at any time. One
of the small connectors is used to substitute for the load of
the driver air bag assembly when it is connected at the top
of the column to the SRS coil assembly. Another small
connector is used to substitute for the load of the driver air
bag assembly and the SRS coil assembly when it is
connected at the base of the column to the SRS wiring
harness. The third small connector is used to substitute
for the load of the passenger air bag assembly and
pretensioner seat belt assembly when connected to the
passenger air bag assembly and pretensioner seat belt
assembly harness connector.
By substituting the resistance of the load tool when called
for, a determination can be made as to whether an inflator
circuit component is causing system malfunction and
which component is causing the malfunction. The loadtool should be used only when specifically called for in the
diagnostic procedures.
NOTE: If comand to use 5±8840±2421±0 load tool when
repair the pretensioner seat belt, connect load tool
connector to use for driver air bag and/or passenger air
bag connector.
5±8840±0285±0 DVM
901RS153The 5±8840±0285±0 DVM is the preferred DVM for use in
SRS diagnosis and repair. However, 5±8840±0366±0
may be used if 5±8840±0285±0 is not available. No other
DVMs are approved for SRS diagnosis and repair.
Scan Tool
901RW176The Tech 2 is used to read and clear SRS Diagnostic
Trouble Codes (DTCs). Refer to the Tech 2 Operators,
Manual for specific information on how to use the Tech 2.