Circuit/System Description
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The trailer brake control module (TBCM) monitors the 12V system voltage to make sure that the voltage stays within the proper range. Damage to components, and incorrect data can occur when the voltage is out of range. The TBCM monitors the system voltage. If the TBCM detects a 12V system voltage outside an expected range, DTC C0800 will set.