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 primary manual apply switch circuit diagnostic monitors for circuit faults on the primary manual apply switch input to the trailer brake control module (TBCM).
This DTC will also be set as current DTC when a fault is detected in 5-volt reference voltage or in TBCM ground circuit.