Air Bag: Description and Operation

Components Description

Airbag Modules

Driver Airbag Module

WARNING: Tempering with driver airbag module creates the risk of an injury from unexpected deployments. Therefore, the driver airbag module should never be disassembled.

The driver airbag module is under the center pad of the steering wheel. The driver airbag module contained an igniter charge and a gas generator to inflate the folded airbag.

Passenger Airbag Module

WARNING: Tempering with passenger airbag module creates the risk of an injury from unexpected deployment. Therefore, the passenger airbag module should never be disassembled. The passenger airbag module is on the passenger part of the instrument panel. The passenger airbag module contains an igniter charge and a gas generator to inflate the folded airbag.





The passenger airbag module is on the passenger part of the instrument panel. The passenger airbag module contains an igniter charge and a gas generator to inflate the folded airbag.

Side Airbag Module

WARNING: Tempering with side airbag module creates the risk of an injury from unexpected deployments. Therefore, the driver airbag module should never be disassembled.




The side airbag modules are in the driver's and passenger's seats. The side airbag module contains an igniter charge and a gas generator to inflate the folded airbag.

Front Seat Belt Pretensioners

WARNING: Tempering with seat belt pretensioner creates the risk of an injury from unexpected deployment. Therefore, the front seat belt pretensioners should never be disassembled.

The seat belt pretensioners (with load limiter for some vehicles) are assembled with each front seat belt retractors to retract the seat belt webbing when accounted frontal collision. The seat belt pretensioners are controlled by Sensing and Diagnostic Module (SDM). The seat belt pretensioner contains an igniter charge and a gas generator to pull the seat belt webbing. The seat belt pretensioner must be replaced after an accident that causes its activation.

Sensing and Diagnostic Module (SDM) (Air Bag Control Module)

WARNING: During the service procedures, be careful when handling the SDM. Never shake or jar the SDM. Never apply power to SIR when the SDM is not rigidly attached to the vehicle. All SDM mounting bolts and grounding nuts must be fully tightened. Failure to follow these precautions could cause deployment and result in personal injury.

The SDM is located on the floor beneath the floor console assembly. The SDM performs the following functions:
^ Monitors the Supplemental Inflatable Restraints (SIR) electrical components and sets a Diagnostic Trouble Code (DTC) when malfunction is detected.
^ Records any faults that are discovered.
^ Displays SIR diagnostic trouble codes and system status information when connected to a scan tool.
^ Illuminates the airbag indicator to alert the driver to any fault.
^ Provides a reserve power source to deploy the airbags and pretensioners if an accident has disabled the normal power source.
^ Monitors vehicle velocity changes to detect frontal impacts, which are severe enough to warrant deployment.
^ Causes current to flow through the airbag modules and pretensioner to cause deployment if a frontal impact of sufficient force is detected.





The SDM contains no user-serviceable parts.

Airbag Warning Lamp

The instrument cluster contains an airbag warning indicator and Sensing and Diagnostic Module (SDM). The SDM performs a turn-ON test when the ignition is turned ON.

The SDM flashes the airbag indicator seven times by supplying an intermittent ground to the indicator lamp circuit. After flashing seven times, the airbag indicator will turn OFF if no more malfunctions have been detected.

If the SDM has detected malfunctions in the internal and external circuits, which could potentially affect the operation of the Supplemental Inflatable Restraints (SIR), the airbag indicator stays ON. Some malfunctions could result in non-deployment when necessary or deployment under conditions which would not normally result in deployment.

When the SDM is not properly attached to its connector, the airbag circuit is shorted to ground because there is a shorting bar in the SDM electrical connector. The shorting bar is disengaged when proper connection is made, but if a poor connection exists the SDM connector supplied a ground to the airbag indicator independently of the SDM, and the airbag indicator turns ON.

Clock Spring

WARNING: Disassembling the clock spring can cause injury or cause the clock spring to malfunction.

CAUTION: Over-rotating the clock spring (over 3 and one quarter turns to one direction) without the steering wheel in position could damage the clock spring and result in an inoperative driver airbag.

There is a coil assembly in the steering which is referred to as a clock spring because of its internal resemblance to the type of spring used in a mechanical clock. The coil spring should never be disassembled, and there is no timekeeping function. The clock spring contains two or three current-carrying coils. One of the current-carrying coils maintains continuous contact within the driver deployment loop while the steering wheel is rotated. The clock spring also contains coils that maintain continuous contact for horn and remote audio control switch circuit.

Turning the steering wheel in one direction tightens the coil, and turning the steering wheel in the opposite direction loosens the coil. Do not turn the clock spring when the steering wheel is not attached. Refer to => Clock Spring Removal and Installation for proper installation of the clock spring.





The clock spring also includes the wiring and the connectors for the horn circuit and the driver airbag circuit. A yellow two-way connector on the lower steering column is attached to the clock spring wiring.

Occupants Classification System (OCS)

OCS determines passenger airbag deployment. It consists of a sensor and module which are in the passenger seat.

OCS monitors the pressure profile of the passenger seat and send it to the Sensing and Diagnostic Module (SDM).

When the pressure from the occupant s weight is higher than a specified value, the OCS module will send an enable signal to the SDM to deploy the passenger airbag.

When the passenger airbag off symbol is lit on the passenger airbag status indicator, it means the suppression of deployment for the passenger's frontal airbag and side airbag.

OCS is not unit repairable so it should be replaced with an assembly of passenger seat.

Early Crash Sensor (ECS)

ECSs are located on both LH and RH side of longitudinal.
ECS detects frontal impact of the vehicle and transmits the information to the SDM.

Wiring Harness Connectors

If the Sensing and Diagnostic Module (SDM) electrical connector is not attached properly, a built in shorting bar will connect the wire from airbag warning lamp with the SDM ground wire. This turns ON the airbag indicator.

The shorting bar is only a backup safety device. Always disable the Supplemental Inflatable Restraints (SIR) before beginning any service procedure.