2002 ISUZU AXIOM Service Repair Manual

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
BAGª 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 30
degrees off the centerline of the vehicle. The air bagassemblies 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.
D09R200001

SUPPLEMENTAL RESTRAINT SYSTEM 9J±4
SRS Component and Wiring Location
View
060R200036
Legend
(1) Battery
(2) Relay & Fuse Box
(3) Passenger Air Bag Assembly
(4) SDM
(5) Meter Assembly
(6) SRS Coil Assembly
(7) Driver Air Bag Assembly
(8) Starter Switch
(9) Fuse Box, SRS±1
Component Description
SDM (Sensing and Diagnostic Module)
WARNING:DURING SERVICE PROCEDURES, BE
VERY CAREFUL WHEN HANDLING A SENSING AND
DIAGNOSTIC MODULE (SDM). NEVER STRIKE OR
JAR THE SDM. NEVER POWER UP THE SRS WHEN
THE SDM IS NOT RIGIDLY ATTACHED TO THE
VEHICLE. ALL SDM AND MOUNTING BRACKET
FASTENERS MUST BE CAREFULLY TORQUED AND
THE ARROW MUST BE POINTED TOWARD THE
FRONT OF THE VEHICLE TO ENSURE PROPER
OPERATION OF THE SRS. THE SDM COULD BE
ACTIVATED WHEN POWERED WHILE NOT RIGIDLYATTACHED TO THE VEHICLE WHICH COULD CAUSE
DEPLOYMENT AND RESULT IN PERSONAL INJURY.
The Sensing and Diagnostic Module (SDM) is designed
to perform the following functions in the SRS:
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.
827RW023

SUPPLEMENTAL RESTRAINT SYSTEM9J±5
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 flashing SEVEN
(7) times 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 BAGº 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.
060R200035
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.
825RS071
Air Bag Assemblies
The air bag assembly consist of an inflatable air bag
assembly and an inflator (a canister of gas±generating
material and an initiating device). When the vehicle is in a
frontal crash of sufficient force.
The SDM causes current flow through the deployment
loops. Current passing through the inflator ignites the
material in the air bag assembly. The gas produced from
this reaction rapidly inflates the air bag assembly.
There is a shorting clip on the driver air bag assembly
connector which connects the SRS coil assembly. The
shorting clip shorts across the driver air bag assembly
circuits when driver air bag assembly 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 driver air bag assembly, the steering
column or other SRS components.
827RX001

SUPPLEMENTAL RESTRAINT SYSTEM 9J±6
There is a shorting clip on the passenger air bag
assembly connector which connects to the SRS harness.
The shorting clip shorts across the passenger air bag
assembly circuit when the passenger air bag assembly
connector is disconnected. The circuit to the passenger
air bag assembly is shorted in this way to help prevent
unwanted deployment of the air bag when servicing the
passenger air bag assembly, the instrument panel or
other SRS components.
827RY00001
Legend
(1) Passenger Air Bag Door
(2) Passenger Air Bag Assembly
(3) Passenger Air Bag Harness
(4) Cross Beam
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.
431R200006
Knee Bolster
The knee bolsters are used to absorb energy to protec
knees and control the forward movement of the vehicle's
front seat occupants during a frontal crash, by limiting leg
movement.
740RS021
Definition
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 flash
seven times 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.

SUPPLEMENTAL RESTRAINT SYSTEM9J±7
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
Electronically 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 Monitoring.º This test checks for the correct
SDM configuration for the vehicle, shorts to ªIgnition 1º in
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 onboard 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
NON±POWERED PROVE±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

SUPPLEMENTAL RESTRAINT SYSTEM 9J±8
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 PROVE±TYPE TESTER. INSTRUCTIONSIN 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 J±41433, Connector Test
Adapter Kit J±35616±A, and the DVM (Digital Multimeter)
J±39200.
SRS Connector Body Face Views
D09RW003
Legend
(1) SDM
(2) Driver Air Bag Assembly
(3) Passenger Air Bag Assembly(4) ªAir Bagº Warning Lamp
(5) SRS Coil Assembly
(6) DLC
Repairs and Inspections Required
After an Accident
NOTE: If any SRS components are damaged, they must
be replaced. If SRS component mounting points are
damaged, they must be replaced.

Never use SRS parts from another vehicle. This does
not include remanufactured parts purchased from an
authorized dealer; they may be used for SRS repairs.
Do not attempt to service the SDM, the SRS coil
assembly, or the air bag assembly. Service of these
items is by replacement only.

Verify the part number of replacement air bag
assembly.
CAUTION: Never use the air bag assembly from
another vehicle and difference model year air bag
assembly.
The air bag assembly has identification colors on the
bar code label as follows.

SUPPLEMENTAL RESTRAINT SYSTEM9J±9
Light blue color for driver air bag assembly.
Light blue color for passenger air bag assembly.
Use only the air bag assembly for AXIOM (UP) mod-
els.
CAUTION: Proper operation of the sensors and
Supplemental Restraint System (SRS) requires that
any repairs to the vehicle structure return it to the
original production configuration. Deployment
requires, at a minimum, replacement of the SDM, air
bag assembly and dimensional inspection of the
steering column. Any visible damage to the SDM
mounting bracket (s) requires replacement, and the
steering column must be dimensionally inspected,
whether deployment occurred or not.
Accident With Deployment ± Component
Replacement and Inspections
Certain SRS components must be replaced or inspected
for damage after a frontal crash involving air bag
deployment. Those components are:

Air bag assembly

SDM
CAUTION: Refer to ªSDM Replacement Guidelinesº
below for important information on SDM
replacement in both deployment and non
deployment crashes.

SRS coil assemblyÐInspect wiring and connector for
any signs of scorching, melting, or damage due to
excessive heat. Replace if damaged. Refer to SRS
coil assembly in this section.
Accident With or Without
DeploymentÐComponent Inspection
Certain SRS and restraint system components must be
inspected after any crash, whether the air bag deployed
or not. Those components are:

Steering columnÐDimensionally inspect per
ªChecking Steering Column for Accident Damageº in
3 of this workshop manual.

Knee bolsters and mounting pointsÐ Inspect for any
distortion, bending, cracking, or other damage.

I/P steering column reinforcement plateÐ Inspect for
any distortion, bending, cracking, or other damage.

I/P bracesÐInspect for any distortion, bending,
cracking, or other damage.

Seat belts and mounting pointsÐRefer to ªSeat
Beltsº in 10 of this workshop manual.
SDM Replacement Guidelines
SDM replacement policy requires replacement of SDM,
after crash involving air bag deployment when ªSRS
Warning Lampº turn ªONº, ªSRS Diagnosisº should be
done according to ªSection 9J1º.
Wiring Damage
If any SRS wire harness is damaged, it should be
replaced. Don't repair SRS. It is replace only.
SRS Connector (Plastic Body And
Terminal Metal Pin) Damage
If any connector or terminal in the SRS wire harness
(except pigtails) is damaged, it should be replaced.
SRS Wire Pigtail Damage
If the wiring pigtail (a wire or wires attached directly to the
device, not by a connector) is damaged, the entire
component (with pigtail) must be replaced. Examples of
ªpigtailº components are the driver air bag assembly, the
passenger air bag assembly, and the SRS coil assembly.
On±Vehicle Service
Service Precautions
WARNING: WHEN PERFORMING SERVICE ON OR
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 SDM in DriverÐPassenger SRS can maintain
sufficient voltage to cause a deployment for up to 15
seconds after the ignition switch is turned ªOFFº, the
battery is disconnected, or the fuse powering the SDM is
removed.
Many of the service procedures require removal of the
ªSRS±1º 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 ªDisabling the SRSº
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 ªlockº and remove key.
1. Remove SRS fuse SRS±1, from left dash side lower
fuse block or disconnect battery.
2. Disconnect yellow 2±pin connector at the base of
steering column.
3. Remove glove box assembly, Refer to ªPassenger Air
Bag Assembly Replacementº in section 9J±28.
4. Disconnect yellow 2±pin connector behind the glove
box assembly.
CAUTION: With the ªSRS±1º fuse removed and
ignition switch ªONº, ªAIR BAGº warning lamp will
be ªONº. This is normal operation and does not
indicate an SRS malfunction.
Enabling The SRS
Installation
CAUTION: Never use the air bag assembly from
another vehicle and difference model year air bag
assembly.

SUPPLEMENTAL RESTRAINT SYSTEM 9J±10
The air bag assembly has identification colors on the
bar code label as follows.
Light blue color for driver air bag assembly.
Light blue color for passenger air bag assembly.
Use only the air bag assembly for AXIOM (UP) mod-
els.
Turn ignition switch to ªLOCKº and remove key.
1. Connect yellow 2±pin connector passenger air bag
assembly.
2. Install glove box assembly, refer to ªPassenger Air
Bag Assembly Replacementº in section 9J±28.
3. Connect yellow 2±pin connector at the base of
steering column.
4. Install ªAIR BAGº fuse SRS±1 to left dash side lower
fuse block or connect battery.
Turn ignition switch to ªONº and verify that the ªAIR BAGº
warning lamp flashes seven times and then turns ªOFFº If
it does not operate as described, perform the ªSRS
Diagnostic System Checkº in section 9J1±3.
Handling / Installation / Diagnosis
1. Air bag assembly should not be subjected to
temperatures above 93
C (200
F).
2. Air bag assembly, and SDM should not be used if they
have been dropped from a height of 100 centimeters
(3.28 feet).
3. When a SDM is replaced, it must be oriented with the
arrow on the sensor pointing toward the front of the
vehicle. It is very important for the SDM to be located
flat on the mounting surface, parallel to the vehicle
datum line. It is important that the SDM 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 ªSRS Diagnostic System Checkº must be the
starting point of any SRS diagnostics. The ªSRS
Diagnostic System Checkº will verify proper ªAIR
BAGº warning lamp operation and 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.
Air Bag Assembly Handling /
Shipping / Scrapping
Live (Undeployed) Air Bag Assembly
Special care is necessary when handling and storing a
live (undeployed) air bag assembly. The rapid gas
generation produced during deployment of the air bag
could cause the air bag assembly, or an object in front of
the air bag assembly, to be thrown through the air in the
unlikely event of an accidental deployment.
827RW009
WARNING: W H E N C A R RY I N G A L I V E A I R B A G
ASSEMBLY, MAKE SURE THE BAG OPENING IS
POINTED AWAY FROM YOU. IN CASE OF AN
ACCIDENTAL DEPLOYMENT, THE BAG WILL THEN
DEPLOY WITH MINIMAL CHANCE OF INJURY.
NEVER CARRY THE AIR BAG ASSEMBLY BY THE
WIRES OR CONNECTOR ON THE UNDERSIDE OF
THE MODULE.
827RS044