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I’ve got a 2010 duramax and every time I start my truck it says service trailer break system. But when I hook my trailer up and start my truck with my foot on the break it comes across the dash saying “trailer connected” and the trailer breaks work fine until I take my foot all the way off the break pedal then the truck dings and shows the message “service trailer break system” Ive traced wired all around and I’m at a loss now don’t know what too try next and don’t wanna pay an arm and a leg for a shop too maybe fix it.
I had the same problem. It turned out to be a relay
I’ve got a 2010 duramax and every time I start my truck it says service trailer break system. But when I hook my trailer up and start my truck with my foot on the break it comes across the dash saying “trailer connected” and the trailer breaks work fine until I take my foot all the way off the break pedal then the truck dings and shows the message “service trailer break system” Ive traced wired all around and I’m at a loss now don’t know what too try next and don’t wanna pay an arm and a leg for a shop too maybe fix it.
I had the same problem. It turn out to be the trailer brake relay. It’s on the driver side frame back beside spare tire. Should be a module and the relay there together.
 

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I cleaned the 7 prong and used die electric greese and also have replaced the little black box but still haven’t found the problem I also tried too use a buddy’s controller switch and that also didn’t help
  1. I'm having the same problem with my 20071/2 3500 hd SRW. Dealer replaced brake pedal switch and brake line pressure switch without solving the problem. I replaced the trailer brake module located on the frame behind driver side rear wheel. Now I have both codes C0035 and C0040 ( front wheel speed sensors) and U0101 transmission control module communication problem. I have ABS warning light, CEL, and service trailer brake warning on the dic. Lately it throws no start. It got worse when it started raining. I'm waiting for a warm dry day to see if I can get it running and into a shop. My gut tells me it's a damp corroded connector but not in the back. Keep me posted on your progress. My email is [email protected].
 

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  1. I replaced the trailer brake module located on the frame behind driver side rear wheel. I have ABS warning light,
New TBCM modules require programming. The fact that yours apparently wasn't programmed is a likely cause of having the ABS warning light on. Any time the ABS warning light is on, you will get the SERVICE TRAILER BRAKE SYSTEM message on your DIC.

Fix the programming, see if your ABS warning light goes away and when it does, you will likely not have the STBS message any longer. If you do continue to have STBS message, then you can work on the TBCM system to see what the problem is there.
 

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Good catch, to complete the story ... I first replaced the tbcm which didn't help, then took it to the dealership for repair. They replaced the brake pedal switch and the pressure switch on the master cylinder. Still not fixed. The dealership consulted with GM factory and determined the abs control module at fault. I had the abs module replaced and reprogrammed the system. All worked great for about a week when the dic began with the service trailer brake system warning. The cruise control became intermittent and via my OnStar connection determined the cO035 and c0040 as well as the u0101 code. These appeared after driving on a rainy day. The vehicle also has given a service 4wd message on the dic but only transient and no codes. A couple days ago it failed to start or crank. I'm waiting for dry condition to see if moisture may be the problem. Let me know what you think.
 

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I had the same message an it pop up while filling up on fuel stop filled up truck ,started it put it in drive an wham message came up with no trailer connected. Mine was due the ABS computer not getting data from all the sensors none of those code readers from AZ , Napa ,advance auto would find it had to take it to the shop that had the professional code reader that reads all the computers on the truck. That was the only way they found that the front wheel sensor was not providing any data
 

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I’ve got a 2010 duramax and every time I start my truck it says service trailer break system. But when I hook my trailer up and start my truck with my foot on the break it comes across the dash saying “trailer connected” and the trailer breaks work fine until I take my foot all the way off the break pedal then the truck dings and shows the message “service trailer break system” Ive traced wired all around and I’m at a loss now don’t know what too try next and don’t wanna pay an arm and a leg for a shop too maybe fix it.
Could be a fuse. And if you have the led strips under your your tailgate that could be messing with the computer saying there’s a trailer on when it’s just lights
 
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