Circuit/System Description
WARNING: This page is about a different car, the 2017 Cadillac ATS. However, it is still accessible from the selected car via links, so may be relevant.
The brake pedal position sensor signal circuit is a B+ input from the body control module (BCM) to the engine control module (ECM). The BCM and ECM monitor the brake pedal position sensor signal circuit to detect when the brake pedal has been applied. When the brake pedal is applied, the BCM supplies B+ on the stop lamp signal circuit and also sends a serial data message to the ECM indicating that the brake pedal has been applied.