2007.5 2500hd OEM trailer brakes are not working correctly. A few details:
1. It is truck-side. I hooked up a different truck to my trailer, and the brakes worked.
2. I replaced the trailer brake module and the relay located by the back tire and also checked the fuses.
3. The trailer brakes work if I start the truck while holding the brake. Then as long as I continue to press the brake, they work.
4. Once I let go of the brakes for more than 3 seconds, a notification comes on the dash saying "Service Trailer Brake System." If I press the brakes after this point, the trailer brakes do not work.
Any help would be appreciated.
Thanks!