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 trailer brake apply switch is shorted to ground, shorted to battery, or open circuit, DTC C1116 Manual Apply Switch Primary input circuit fault may also be set as a current DTC. If DTC C1116 is also set as current DTC, then diagnose DTC C1116 first before to diagnosing DTC C1115 08 and C1115 5A. 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.