Circuit/System Description
WARNING: This page is about a different car, the 2010 Cadillac SRX. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) activates the serial data communication enable circuit when the ignition key is in ACC, ON or START. The serial data communication enable circuit wakes up the engine control module (ECM) for serial data bus communication.