Frontal SIR System Description

WARNING: This page is about a different car, the 2004 Chevrolet Monte Carlo and 2004 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.

The frontal SIR system consists of the following components:

AIR BAG indicator located in the instrument panel cluster (IPC)
Driver and front passenger knee bolsters
Inflatable restraint front end sensor also known as the electronic frontal sensor (EFS)
Inflatable restraint instrument panel (I/P) module
Inflatable restraint sensing and diagnostic module (SDM)
Inflatable restraint steering wheel module
Inflatable restraint steering wheel module coil
Inflatable restraint wiring harnesses
Steering wheel and steering column

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.