The supplemental inflatable restraint (SIR) system supplements the protection offered by the occupant seat belt system (2). The SIR system contains various inflator modules located throughout the vehicle, i.e. inflatable restraint steering wheel module (1) and the inflatable restraint IP module (1). Each inflator module has a deployment loop that is controlled by the inflatable restraint sensing and diagnostic module (SDM), which is mounted inside of the vehicle. The SDM determines the severity of a collision and commands deployment of each inflator module. The SDM performs continuous diagnostic monitoring of the SIR system electrical components. Upon detection of a circuit malfunction, the SDM will set a diagnostic trouble (DTC) and inform the driver by commanding the instrument panel cluster (IPC) to turn the AIR BAG indicator ON. The steering column and knee bolsters (3) are designed to absorb energy and compress during frontal collisions in order to limit leg movement and decrease the chance on injury to the driver and front passenger.

The frontal SIR system consists of the following components:

A frontal collision of sufficient force will deploy the inflator modules. The SDM contains a sensing device (accelerometer) that converts vehicle velocity changes to an electrical signal. The SDM contains a microprocessor, which performs calculations using the measured accelerations and compares these calculations to a value stored in memory. When the generated calculations exceed the stored value, the SDM will cause current to flow through the deployment loops, deploying the inflator modules. Once the inflator modules are inflated, they quickly deflate through the air bag vent holes and/or the bag fabric. After the inflator modules are deployed, the SDM sets a deployment commanded DTC and then commands the IPC to turn the AIR BAG indicator ON. The SDM, IP module, steering wheel module, steering wheel module coil and the connecting wires make up the deployment loops. The SDM continuously monitors the deployment loops for malfunctions and commands the IPC to turn the AIR BAG indicator ON if a fault is detected.

The inflatable restraint sensing and diagnostic module (SDM) is a microprocessor and the control center for the SIR system. The SDM contains internal sensors along with external sensors, if equipped, mounted at various locations, depending on vehicle. In the event of a collision, the SDM performs calculations using the signals received from the internal and external sensors, if equipped. The SDM compares the result of the calculations to values stored in memory. When these calculations exceed the stored value, the SDM will cause current to flow through the deployment loops, deploying the inflator modules. The SDM records the SIR system status when a deployment occurs and commands the IPC to turn the AIR BAG indicator ON. The SDM performs continuous diagnostic monitoring of the SIR system electrical components and circuitry when the ignition is ON. If the SDM detects a malfunction, a DTC will be stored and the SDM will turn the AIR BAG indicator ON. In the event that ignition 1 voltage is lost during a collision, the SDM maintains a 23 volt loop reserve (23 VLR) for deployment of the inflator modules. It is important to note, when disabling the SIR system for service or rescue operations, to allow the 23 VLR to dissipate, which could take up to 1 minute.

The AIR BAG indicator, located in the IPC is used to notify the driver of SIR system malfunctions. When the ignition is turned ON, the SDM is supplied with ignition 1 voltage. The SDM flashes the AIR BAG indicator seven times. While flashing the AIR BAG indicator, the SDM conducts tests on all SIR system components and circuits. If no malfunctions are detected, the SDM will turn the AIR BAG indicator OFF. The SDM provides continuous monitoring of the inflator module circuits by conducting a sequence of checks. If a malfunction is detected, the SDM will store a diagnostic trouble code (DTC) and turn the AIR BAG indicator ON. The presence of a SIR system malfunction could result in non-deployment of the inflator modules. The AIR BAG indicator will remain ON until the malfunction has been repaired.

The AIR BAG indicator is the key to driver notification of SIR system malfunctions. The AIR BAG indicator is used to inform the driver of the proper operation of the SIR system. The SDM uses the AIR BAG indicator to do the following:

The inflator modules consist of a housing, an inflatable air bag, the initiator, a canister of gas generating materials, and in some cases, stored compressed gas. The initiator is part of the inflator module deployment loop. When the vehicle is involved in a collision of sufficient force, the SDM causes current to flow through the deployment loops to the initiator. Current passing through the initiator ignites the material in the canister producing a rapid generation of gas and the release of compressed gas, if present. The gas produced from this reaction rapidly inflates the inflator module. Once the inflator module is inflated, it quickly deflates through the vent holes and/or the fabric. Each inflator module is equipped with a shorting bar that is located in the connector of the inflator module. The shorting bar shorts the inflator modules circuitry to prevent unwanted deployment of the inflator module when the connector is disconnected.

The steering wheel module coil is attached to the steering column and is located under the steering wheel. The steering wheel module coil consists of two or more current-carrying coils. The coils allow the rotation of the steering wheel while maintaining continuous electrical contact between the steering wheel module deployment loop and the steering wheel module. Two coil wires are used for the steering wheel module deployment loop. Additional coil wires are used for accessories that are attached to the steering wheel, depending on the vehicle model. The steering wheel module coil connector is located near the base of the steering column. The connector contains a shorting bar that shorts the steering wheel module coil deployment loop circuitry to prevent unwanted deployment of the steering wheel module when the connector is disconnected.

The inflatable restraint wiring harness connects the inflator modules, the SDM, the deployment loops, and the serial data circuit together using weather - packed connectors. SIR system connectors are yellow for easy identification. When repairing SIR wiring harnesses, follow the proper testing and repair procedures listed in the service manual.

The steering wheel and column are designed to absorb energy when driver contact is made with steering wheel or inflated module. In a collision, the driver may contact the steering wheel directly or load the steering wheel and column through the inflated module. When the driver applies load to the inflator module or the steering wheel, the column will compress downward, absorbing some of the impact and helping to reduce bodily injuries to the driver. The steering wheel and column must be inspected for damages after a collision.

The knee bolsters are designed to help restrain the lower torso of front seat occupants by absorbing the energy through the front seat occupant's upper legs. In a collision, the front seat occupant's legs may come in contact with the knee bolsters. The knee bolsters are designed to crush and deform, absorbing some of the impact and helping to reduce bodily injuries. The driver and passenger knee bolsters are located in the lower part of the instrument panel and must be inspected for damages after a collision.