Supplemental Inflatable Restraints (SIR)
The supplemental inflatable restraints (SIR) is a safety device used in conjunction with the seat belt. The air bag does not replace the function of the seat belt. The driver and the passengers must always fasten their seat belts and 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:
| • | Driver air bag module |
| • | Driver side air bag module |
| • | Passenger air bag module |
| • | Passenger side air bag module |
| • | Driver's and front passenger's seat belt pretensioners, and load limiter for some models |
| • | Sensing and diagnostic module (SDM) |
| • | Clock spring |
| • | Wire harness and connectors |
| • | AIR BAG indicator on the instrument cluster |
| • | Side air bag sensor |
Air Bag Modules
Driver Air Bag Module
Caution: Refer to SIR Caution in the Preface section.
The driver air bag module is under the center pad of the steering wheel. The driver air bag module contains an igniter charge and a gas generator to inflate the folded air bag.
The air bag connector contains a shorting bar, which makes the circuit shorted when the connector is disconnected. The shorting bar prevents current from travelling through the driver air bag module during servicing. The shorting bar is disengaged when the connector is connected.
Passenger Air Bag Module
Caution: Refer to SIR Caution in the Preface section.
The passenger air bag module is on the passenger part of the instrument panel. The passenger air bag module contains an igniter charge and a gas generator to inflate the folded air bag.
The air bag connector contains a shorting bar, which makes the circuit shorted when the connector is disconnected. The shorting bar prevents current from travelling through the passenger air bag 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's and passenger's seats. The side air bag module contains an igniter charge and a gas generator to inflate the folded air bag
The air bag connector contains a shorting bar, which makes the circuit shorted when the connector is disconnected. The shorting bar prevents current from travelling through the side air bag module during servicing. The shorting bar is disengaged when the connector is connected.
Front Seat Belt Pretensioners
Caution: Refer to SIR Caution in the Preface section.
The seat belt pretensioners, with load limiters for some vehicles, are assembled with each front seat belt retractors to retract the seat belt webbing when encountering a frontal collision. The seat belt pretensioners are controlled by the 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 travelling through the seat belt pretensioner during servicing. The shorting bar is disengaged when the connector is connected.
Sensing and Diagnostic Module (SDM)
Caution: Refer to SRS Sensing and Diagnostic Module Handling Caution in the Preface section.
The SDM is located on the floor beneath the floor console assembly. The SDM performs the following functions:
| • | Monitors the SIR electrical components and sets a 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 air bag indicator to alert the driver to any fault |
| • | Provides a reserve power source to deploy the air bags 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 air bag modules and pretensioner to cause deployment if a frontal impact of sufficient force is detected |
The SDM contains no user-serviceable parts.
Air Bag Warning Lamp
The instrument cluster contains an air bag warning indicator and SDM. The SDM performs a turn-on test when the ignition is turned ON.
The SDM flashes the air bag indicator 7 times by supplying an intermittent ground to the indicator lamp circuit. After flashing 7 times, the air bag 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 SIR, the air bag 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 air bag circuit is shorted to ground because there is a shorting bar in the SDM electrical connector. The shorting bar is disengaged when a proper connection is made, but if a poor connection exists, the SDM connector supplied a ground to the air bag indicator independently of the SDM, and the air bag indicator turns ON.
Clock Spring
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.
Notice: Do not rotate the steering wheel or move the position of the steering gear once the intermediate shaft is disconnected. This will uncenter the Inflatable Restraint coil in the steering column. If the Inflatable Restraint coil becomes uncentered, it may be damaged during vehicle operation.
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 2-3 current-carrying coils. One of the current-carrying coils maintains continuous contact within the driver deployment loop while the steering wheel is rotated. The clock spring also contains coils that maintain continuous contact for horn and remote audio control switch circuit.
Turning the steering wheel in 1 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 Inflatable Restraint Steering Wheel Module Coil Replacement for proper installation of the clock spring.
The clock spring also includes the wiring and the connectors for the horn circuit and the driver air bag circuit. A yellow 2-way connector on the lower steering column is attached to the clock spring wiring. The yellow connector to the air bag 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 driver air bag module during servicing. The shorting bar is disengaged when the clock spring connector is connected.
Wiring Harness Connectors
If the SDM electrical connector is not attached properly, a built in shorting bar will connect the wire from the 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 the following locations:
| • | The clock spring electrical connector at the lower steering column |
| • | The passenger air bag module |
| • | The driver air bag module |
| • | The seat belt pretensioners |
The shorting bar is only a backup safety device. Always disable the SIR before beginning any service procedure.
