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 trailer brake control module (TBCM) monitors the system voltage (ignition voltage) to make sure that the voltage stays within the proper range. Damage to components, and incorrect data input can occur when the voltage is out of range. The TBCM monitors the system voltage over an extended length of time. If the TBCM detects a system voltage outside an expected range, DTC C0800 will set.