Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Manual - part 505

SUPPLEMENTAL RESTRAINT SYSTEM

9J–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 “AIR
BAG“ 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 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.

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 RIGIDLY

ATTACHED 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 — 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 — The SDM monitors

vehicle velocity changes to detect frontal crashes
which are severe enough to warrant deployment.

3. Air Bag Deployment — 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 — The SDM performs

diagnostic monitoring of SRS electrical components
and sets a diagnostic trouble code when a
malfunction is detected.

5. Frontal Crash Recording — The SDM records

information regarding SRS status during frontal
crash.

6. Malfunction Diagnosis — The SDM displays SRS

diagnostic trouble codes and system status
information through the use of a scan tool.

7. Driver Notification — The SDM warns the vehicle

driver of SRS malfunctions by controlling the “Air
Bag” 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 “AIR BAG” 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 “AIR BAG” warning lamp to come “ON” steady
whenever the ignition switch is at the ON or START
positions with the SDM disconnected.

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SUPPLEMENTAL RESTRAINT SYSTEM

9J–5

“Air Bag” Warning Lamp

Ignition voltage is applied to the “AIR BAG” 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 “AIR BAG” 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 “ON”.

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 “AIR BAG” warning lamp is the key to driver
notification of SRS malfunctions.  For proper lamp
operation, refer to the “SRS Diagnostic System Check” 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
“ON” 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 “AIR BAG” warning lamp to flash
seven times and then go “OFF” whenever the ignition
switch transitions to the ON position from any other
ignition switch position and no malfunctions are detected.

“CONTINUOUS MONITORING”
Tests performed by the SDM on the SRS every 100
milliseconds while “Ignition 1” voltage is in the normal
operating voltage range at the SDM.

Data Link Connector (DLC)
Formerly “DLC” 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.