Circuit/System Description
WARNING: This page is about a different car, the 2009 Saturn Outlook, 2009 GMC Acadia, 2009 Chevrolet Traverse, and 2009 Buick Enclave. However, it is still accessible from the selected car via links, so may be relevant.
The stop lamp switch signal circuit is a direct hardwire input from the body control module (BCM) to the engine control module (ECM) and the transmission control module (TCM). The modules monitor the stop lamp switch signal circuit to detect when the brake pedal has been applied. The BCM monitors the brake apply sensor signal circuit to determine when the brake pedal is applied. When the brake pedal is applied, the BCM sends a serial data message to the modules and also a voltage signal on the stop lamp switch signal circuit indicating that the brake pedal has been applied.