SERVICE TRAILER BRAKE SYSTEM MESSAGE APPEARS AS SOON AS IGNITION IS TURNED ON
I HAVE A U1556 CODE
I REMOVED SPARE TIRE AND INSPECTED THE TBCM & HARNESS. THERE IS A BULLETIN. NO PROBLEMS FOUND
I REPLACED THE TRAILER BRAKE CONTROL MODULE(AC DELCO),7 WAYHARNESS AND TRAILER PLUG
STILL HAVE SAME ISSUE
ANY HELP WOULD BE APPRECIATED
THANK YOU