Circuit/System Description
WARNING: This page is about a different car, the 2013 Chevrolet Trax and 2013 Buick Encore. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) monitors the brake pedal position sensor. When the brake pedal is applied, the BCM detects a predetermined voltage signal. The BCM sends a serial data message to the engine control module (ECM) indicating the status of the stop lamps.