SIR System Description and Operation. Chevrolet Joy 2008

For 1990-2009 cars

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:

• | Steering wheel module

• | Driver side air bag module

• | Instrument panel (I/P) module

• | Passenger side air bag module

• | Driver and front passenger seat belt pretensioners (and load limiter for some model)

• | Sensing and diagnostic module (SDM)

• | Steering wheel module coil

• | Wire harness and connectors

• | AIR BAG indicator on the instrument cluster

• | Side impact sensor

### Air Bag Modules

#### 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 charge and a gas generator to inflate the folded air bag.

The air bag contains a shorting bar, which makes the circuit shorted when the connector is disconnected. The shorting bar prevents current from travelling through the steering wheel module during servicing. The shorting bar is disengaged when the connector is connected.

#### Instrument Panel (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 connector contains a shorting bar, which makes the circuit shorted when the connector is disconnected. The shorting bar prevents current from travelling 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 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: When performing service on or near the SIR components or the SIR wiring, the SIR system must be disabled. Refer to SIR Disabling and Enabling . Failure to observe the correct procedure could cause deployment of the SIR components, personal injury, or unnecessary SIR system repairs.

The seat belt pretensioners, with a load limiter for some vehicles, are assembled with each front seat belt retractor to retract the seat belt webbing when encountered 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 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 Sensing and Diagnostic Module Handling Caution in the Preface section.

The sensing and diagnostic module (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 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 driver information center (DIC) contains an air bag warning indicator to verify the operation of the supplemental inflatable restraints (SIR) system. The sensing and diagnostic module (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 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 proper connection is made, but if a poor connection exists the SDM connector supplies a ground to the air bag indicator independently of the SDM, and the air bag indicator turns on.

### Steering Wheel Module Coil

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 coil spring should never be disassembled, and there is no timekeeping function. The steering wheel module coil 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 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.

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 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 steering wheel module during servicing. The shorting bar is disengaged when the steering wheel module coil connector is connected.

### 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 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 steering wheel module coil electrical connector at the lower steering column

• | The instrument panel (I/P) module

• | The steering wheel module

• | The seat belt pretensioners

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