Diagnostic Aids
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.
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.
When the manual apply switch 5-volt reference circuit or TBCM ground is open circuit, in addition to setting DTC C1116, DTC C1117 and C1118 may also be set as current DTC. In this case, diagnose the apply switch 5-volt reference circuit or TBCM ground first for open circuit fault before to diagnosing DTC C1117. 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.