Lazarus_Unknown

I have a 2011 Silverado 2500HD 6.0. I have a Service Trailer Brake System light on & i’ve tried replacing the Relay, Control Module, All related fuses including the Stud 1 & Stud 2 fuses. Yet the Service Trailer Brake System light is still on. Does anyone have any more ideas of what I need to check? Note: All my trailer lights work. It’s only the Trailer Brake having issues. Thank you