Sierra 1500 2WD V8-5.3L Hybrid (2004)
Air Bag Control Module: Description and Operation
INFLATABLE RESTRAINT SENSING AND DIAGNOSTIC MODULE (SDM)
The sensing and diagnostic module (SDM) is a microprocessor and the control center for the SIR system. The SDM contains internal sensors along with
several external sensors, if equipped, mounted at various locations on the vehicle. In the event of a collision, the SDM performs calculations using the
signals received from the internal and external sensors. The SDM compares the results of the calculations to values stored in memory. When these
calculations exceed the stored value, the SDM will cause current to flow through the appropriate deployment loops to deploy the air bags. The SDM
records the SIR system status when a deployment occurs and requests the instrument panel cluster (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 turned ON. If the SDM detects a
malfunction, a DTC will be stored and the SDM will request the IPC to 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 air bags. It is important to note, when disabling the SIR
system for servicing or rescue operations to allow the 23 VLR to dissipate, which could take up to 1 minute.
