Air Bag (SIR) System Function and Operation

The Supplemental Inflatable Restraint (SIR) system supplements the protection offered by the driver and front passenger seat belts. The SIR system deploys an air bag from the center of the steering wheel and from the right side of the instrument panel. The knee bolsters and the steering column absorb crash energy. The driver and passenger knee bolsters are below the instrument panel.


The SIR system consists of the following components:

Inflatable Restraint Sensing and Diagnostic Module (SDM)
Inflatable Restraint Steering Wheel Module
Inflatable Restraint Steering Wheel Module Coil
Inflatable Restraint IP Module
AIR BAG warning lamp in the instrument cluster

The inflatable restraint Sensing and Diagnostic Module (SDM), inflatable restraint steering wheel module coil (SIR coil assembly), inflatable restraint steering wheel module (driver inflator module), inflatable restraint IP module (passenger inflator module), and connector wires make up the deployment loops. The function of the deployment loops is to supply current through the inflator modules, which will cause deployment of the air bags. Deployment occurs when the SDM detects vehicle velocity changes severe enough to warrant deployment.

The SDM contains a sensing device (Accelerometer) that converts vehicle velocity changes to an electrical signal. The SDM compares this electrical signal to a value stored in memory. When the generated signal exceeds the stored value, the SDM performs additional signal processing and compares the generated signals to values stored in memory. When two of the generated signals exceed the stored values, the SDM will cause current to flow through the inflator modules, deploying the air bags.

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  • Guest - Donald Hall

    SIR System ,DTC B00074 : Passenger's seat function erratic. SERVICE AIRBAG light on dash is lit. Airbag ON/OFF lights on console comes on when seated, however the ON light goes off within 3 sec but the OFF stays on. I ordered a 360 Airbag bypass module, to se if it will correct the problem. This device place the passenger's seat in constant ON position and will function as if the seat is occupied, passenger's seat AIRBAG is supposed to be ON constantly. SERVICE AIRBAG light should go off the dash without any resetting codes. WE shall see.

  • Guest - ed

    2015 honda crv with airbag code b00AO-87

  • Guest - Tech

    If in fact the clockspring coil is the problem for the code. You need to carefully turn the coil all the way to one end, being sure not to break it, then turn it all the way to the other end. Now divide the number of turns it took to get all the way to the other end in half, and turn it back that number of turns. That will give you the center of the coil position so that it will not break when the steering wheel is turned all the way to the left or right. But the code you have is not usually the coil, it is usually the airbag module itself.

  • Guest - matt

    I have a fault code b1022 on a 1998 Chevy truck. How do I fix it? The clock was replaced with a used one. Is there a way to align it? Thanks.