The supplemental inflatable restraint (SIR) system supplements the protection offered by the occupant seat belt system (2). The SIR system has several inflator modules located throughout the vehicle, i.e. the inflatable restraint steering wheel module (1), inflatable restraint I/P module (1), and the inflatable restraint side impact module - LF. 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 with the assistance of various sensor inputs. When the SDM detects a collision of sufficient force, it will process the information provided by the sensors to further support inflator module deployment. 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 code (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 of 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 frontal inflator modules. The SDM contains a sensing device (accelerometer) that converts vehicle velocity changes to an electrical signal. In some vehicles, the SDM receives a signal from the front end sensor also known as the electronic frontal sensor (EFS) which can help determine the severity of some types of frontal collisions. 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 frontal deployment loops, deploying the frontal 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, I/P module, steering wheel module, steering wheel module coil and the connecting wires make up the frontal 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 36 volt loop reserve (36 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 36 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 and to verify that the SDM is communicating with the IPC. When the ignition is turned ON, the SDM and the IPC are supplied with ignition 1 voltage. The IPC responds by flashing the AIR BAG indicator seven times. While the IPC is flashing the AIR BAG indicator, the SDM conducts tests on all SIR system components and circuits. If no malfunctions are detected, the SDM will command the IPC to turn the AIR BAG indicator OFF via Class 2 serial data. 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 command the IPC to turn the AIR BAG indicator ON via Class 2 serial data. 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 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.

Dual stage inflator modules consist of a housing, inflatable air bag, 2 initiating devices, a canister of gas generating material, and in some cases stored compressed gas. The 2 initiators are part of the frontal deployment loop. The function of the frontal deployment loops are to supply current through the steering wheel and instrument panel (I/P) inflator modules to deploy the air bags. The inflator modules have 2 stages of deployment, which varies the amount of restraint to the occupant according to the collision severity. For moderate frontal collisions, the inflator modules deploy at less than full deployment (low deployment) which consist of stage 1 of the inflator module. For more severe frontal collisions, a full deployment is initiated which consists of stage 1 and stage 2 of the inflator module. The current passing through the initiators ignite the material in the canister producing a rapid generation of gas and in some cases, the release of compressed gas. The gas produced from this reaction rapidly inflates the air bag. Once the air bag is inflated, it quickly deflates through the air bag vent holes and/or the bag fabric. Each dual stage inflator module is equipped with a shorting bar located in the connector(s) of the module. The shorting bar shorts the inflator module deployment loop circuitry to prevent unwanted deployment of the air bag when it 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 2 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 front end sensor also known as the electronic frontal sensor (EFS) is equipped on some vehicles to supplement the SIR system performance. The EFS is an electronic sensor (accelerometer) and is not part of the deployment loops, but instead provides an input to the SDM. The EFS can assist in determining the severity of some frontal collisions. 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 frontal deployment loops, deploying the frontal air bags.

The side impact SIR system consists of the following components:

The side impact modules are located in the outside portion for the front seat backs. The side impact modules consist of a housing, inflatable air bag, initiating device, and a canister of gas generating material. The initiator is part of the side impact module deployment loop. When a side impact of sufficient force occurs, the SIS detects the impact and sends a signal to the SDM. The SDM compares the signal received from the SIS to a value stored in memory. When the generated signal exceeds the stored value, the SDM will cause current to flow through the side deployment loop, deploying the inflator module. The SDM, side impact modules, and the connecting wires make up the side deployment loops. The SDM continuously monitors the side deployment loops for malfunctions and commands the IPC to turn the AIR BAG indicator ON if a fault is present. Each side impact module is equipped with a shorting bar located in the connector of the module. The shorting bar shorts the side impact module deployment loop circuitry to prevent unwanted deployment of the air bag when it is disconnected.

The side impact sensors (SIS) contains a sensing device (accelerometer) which monitors vehicle acceleration and velocity changes to detect side collisions that are severe enough to warrant side inflator module deployment. The SIS is not part of the deployment loop, but instead provides an input to the SDM. The SDM contains a microprocessor that 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 side air bags.

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 the steering wheel or an 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.