Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Circuit/System Description
The brake switch signal circuit is a high voltage input to the body control module (BCM), engine control module (ECM), transmission control module (TCM), Power Take Off (PTO) module (if equipped) and Trailer Brake controller (if equipped). The BCM monitors the stop lamp switch circuit to detect when the brake pedal has been applied. The ECM monitors the brake switch signal to determine when the brake pedal is applied. When the brake pedal is applied, the BCM sends a GMLAN serial data message to the ECM indicating that the brake pedal has been applied. The ECM senses a high voltage signal on the brake switch signal circuit when the stop lamp switch is closed.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.