Circuit/System Description
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The trailer brake control module (TBCM) checks whether there is an ignition ground short fault. This diagnostic compares ignition state with the engine running state received over serial data to determine whether or not there is an ignition ground short fault.