Circuit/System Description
WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The TCC Brake Switch signal hard wired to the TBCM is normally open and closes to battery voltage when the brake pedal is applied. A separate brake switch signal is hard wired to the Body Control Module (BCM) that is normally closed to battery voltage and opens when the brake pedal is applied. The BCM sends its brake switch information to the TBCM over GMLAN serial data. The TBCM compares the states of the two brake switch signals after a Master Cylinder Brake Pressure threshold is exceeded. If the brake switch signal states are not in agreement or if the serial data brake state is not valid, a DTC will set and the ITBC system will be disabled.