The supplemental inflatable restraints (SIR) is safety device used in conjunction with the seat belts. The air bag does not replace the function of the seatbelt. The driver and the passengers must always fasten their seat belts adjust them for a proper fit. The SIR is designed to protect the driver and the front seat passenger in the event of a significant frontal impact to the vehicle. The air bags deploy if the force is applied from a direction within 30 degrees of the vehicle's centerline.

The SIR system consists of the following:

There are 2-4 separate deployment loops in the SIR system. The term loop is used because current leaves the SDM and returns to the SDM during deployment or testing. First loop is the circuit from SDM to the steering wheel module and back to the SDM. Second loop is the circuit from the SDM to the passenger air bag and back to the SDM. The third and fourth loops are for right and left pretensioners.

Steering Wheel Module

Caution: Refer to SIR Caution in the Preface section.

The steering wheel module is under the center pad of the steering wheel. The steering wheel module contains an igniter charger and a gas generator to inflate the folded air bag.

The air bag contains a shorting bar, which short-circuit the driver high circuit to driver low circuit when the connector is disconnected. The shorting bar prevents current from traveling through the steering wheel module during servicing. The shorting bar is disengaged when the connector is connected.

I/P Module

Caution: Refer to SIR Caution in the Preface section.

The instrument panel (I/P) module is on the passenger side of the instrument panel. The I/P module contains an igniter charge and a gas generator to inflate the folded air bag.

The air bag contains a shorting bar, which short-circuit the passenger high circuit to passenger low circuit when the connector is disconnected. The shorting bar prevents current from traveling through the I/P module during servicing. The shorting bar is disengaged when the connector is connected.

Side Air Bag Module

Caution: Refer to SIR Caution in the Preface section.

The side air bag modules are in the driver and passenger front seats. The side air bag modules contain an igniter charge and a gas generator to inflate the folded air bag.

The air bag contains a shorting bar, which short-circuit the high circuit to the low circuit when the connector is disconnected. The shorting bar prevents current from traveling through the side air bag module during servicing. The shorting bar is disengaged when the connector is connected.

Caution: Refer to SIR Caution in the Preface section.

The seat belt pretensioners, with load limiter for some vehicles, are assembled with each front seat belt retractor or buckle to retract the seat belt webbing or buckle when accounted a 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. The seat belt pretensioner also contains a shorting bar to prevent current from traveling through the seat belt pretensioner during servicing. The shorting bar is disengaged when the connector is connected.

Caution: Do not strike or jolt the inflatable restraint sensing and diagnostic module (SDM). Before applying power to the SDM, make sure that it is securely fastened with the arrow facing toward the front of the vehicle. Failure to observe the correct installation procedure could cause SIR deployment, personal injury, or unnecessary SIR system repairs.

The sensing and diagnostic module (SDM) located on floor beneath the floor console assembly. The SDM performs the following functions:

The instrument cluster contains an air bag warning indicator bulb to verify the operation of the AIR BAG indicator and sensing and diagnostic module (SDM). The SDM performs a turn-on test when the ignition is turned ON. The SDM flashes the AIR BAG indicator seven times by supplying an intermittent ground to the indicator lamp circuit. After flashing seven times, the AIR BAG indicator will turn off if no more malfunctions have been detected.

If the SDM has detected malfunctions In the internal or external circuits, which could potentially affect the operation of the supplemental restraint system (SIR), the AIR BAG indicator stays on. Some malfunctions could result in non-deployment when necessary or deployment under conditions which would no normally result in deployment.

When the SDM is not properly attached to its connector, the air bag circuit is shorted to ground because there is a shorting bar within the SDM electronic connector. The shorting bar is disengaged when proper connection is made, but if a poor connection exists the SDM connector supplies a ground to the AIR BAG indicator in dependently of the SDM, and the AIR BAG indicator turns on.

Caution: When servicing the steering column, the Supplemental Inflatable Restraint (SIR) System clock spring must be centered for proper steering wheel operation. Failure to properly center the SIR clock spring may result in reduced turnability of the steering wheel causing the vehicle to improperly maneuver and may cause the SIR system to be inoperative.

There is a coil assembly in the steering which is referred to as a steering wheel module coil because of its internal resemblance to the type of spring used in a mechanical clock. The steering wheel module coil should never be disassembled, and there is no timekeeping function. The steering wheel module coil contains 2 or 3 current-carrying coils. One of the current-carrying coils maintains continuous contact within the driver deployment loop while the steering wheel is rotated. The steering wheel module coil 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 steering wheel module coil when the steering wheel is not attached. Refer to Inflatable Restraint Steering Wheel Module Coil Replacement for proper installation of the steering wheel module coil.

The steering wheel module coil also includes the wiring and the connectors for the horn circuit and the steering wheel module circuit. A yellow 2-way connector on the lower steering column is attached to the steering wheel module coil wiring. The air bag side of the yellow connector contains a shorting bar which connects the driver high circuit to driver low circuit when the connector is disconnected. The shorting bar prevents current from travelling through the steering wheel module during servicing. The shorting bar disengaged when the steering wheel module coil connector is connected.

If the sensing and diagnostic module (SDM) electrical connector is not attached properly, a built in shorting bar will connect the wire from air bag warning lamp with the SDM ground wire. This turns on the AIR BAG indicator. To prevent deployment during servicing, additional shorting bars are located in following locations:

The shorting bar is only a backup safety device. Always disable the supplemental inflatable restraints (SIR) before beginning any service procedure.