Discrete Ignition Signals
WARNING: This page is about a different car, the 2002 Chevrolet Monte Carlo, 2002 Chevrolet Impala, 2001 Chevrolet Monte Carlo, and 2001 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
Those modules that have discrete ignition signal inputs also remain in state dictated by last valid BCM message received on serial data circuits. They check state of their discrete ignition input to determine current valid state. If discrete ignition input is active, battery voltage, modules will fail-safe to run power mode. If discrete ignition input is not active (open or 0 voltage), modules will fail-safe to OFF (awake). In this state modules are constantly checking for a change status message on serial data circuits and can respond to both local inputs and serial data inputs from other modules on vehicle.