Circuit/System Description
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2012 GMC Yukon XL, 2012 GMC Yukon, 2012 Chevrolet Tahoe, 2012 Chevrolet Suburban, and 2012 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition is turned ON, the instrument panel cluster (IPC) flashes the air bag indicator for a bulb check. The inflatable restraint sensing and diagnostic module (SDM) performs diagnostic tests on the SIR system during the bulb check. If any malfunction exists the SDM will request the IPC to illuminate the air bag indicator steady, via serial data. If a preexisting malfunction exists, the air bag indicator will illuminate steady immediately after the ignition is turned ON. If the ignition 1 voltage is outside of the normal operating voltage range 9-16 volts, the SDM will command the IPC to illuminate the air bag indicator with no DTCs present, then disables all deployment loops.