Circuit/System Description
WARNING: This page is about a different car, the 2008 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
The stop lamp switch signal circuit is a high voltage input from the instrument panel module (IPM) to the engine control module (ECM), transmission control module (TCM) and the center high mounted stop lamp (CHMSL). The ECM monitors the stop lamp switch circuit to detect when the brake pedal has been applied. The IPM monitors the brake pedal position sensor to determine when the brake pedal is applied. When the brake pedal is applied, the IPM supplies a high voltage signal on the stop lamp switch signal circuit and also sends a serial data message to the ECM indicating that the brake pedal has been applied. The ECM senses a high voltage signal on the stop lamp switch signal circuit when the brake pedal has been applied.