Sensing & Diagnostic Module (SDM)
WARNING: This page is about a different car, the 2002 Chevrolet Monte Carlo and 2002 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
SDM monitors vehicle velocity changes to detect frontal collisions which are severe enough to warrant air bag module deployment. When a frontal collision of sufficient force is detected, SDM causes current flow through air bag modules to deploy air bags. SDM also maintains a 36 Volt Loop Reserve (36 VLR) energy supply to provide deployment energy for up to one minutes after loss of battery voltage.
Additionally, SDM provides diagnostic monitoring of SIR system electrical components. When a malfunction is detected, SDM sets a Diagnostic Trouble Code (DTC) which can be retrieved using a scan tool. SDM warns driver of system malfunctions by controlling AIR BAG warning light.