Air Bag Control Module: Description and Operation

INFLATABLE RESTRAINT SENSING AND DIAGNOSTIC MODULE (SDM)

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.