Diagnostic Aids

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.

If there are any DTCs set for GMLAN communication such as U0100, U0121, U0140, or U2099, diagnose them first before to resolve DTCs described in this section.

Diagnose an open circuit in trailer brake control module ground circuit or trailer brake control relay ground circuit will also cause DTC C1119 being set as current DTC. When DTC C1119 is set as current DTC, trailer brake control module ground circuit or trailer brake control relay ground circuit should be diagnose for open circuit, before to diagnosing the trailer brake control relay current feedback circuit.

If there is an aftermarket trailer brake controller, the ITBC must be disconnected. Do not power both ITBC and aftermarket controllers to control the trailer brakes at the same time.