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I dont post stuff often but I like to post something when I have a fix to share. I had a SERVICE TRAILER BRAKE SYSTEM message coming on after start up without a trailer hooked up. It came on evertime I started my truck. The funny thing was that if I hooked up my trailer I would NOT get the message and everything worked perfect. But when I disco'd the trailer again the error message would come back. The fix---There was a programming error (dont know how or why it happened) but I had it reprogrammed and it's been right as rain ever since! Just thought I'd share something quick to try before you go for a controller or relay or sensor. I have been finding that the dealers are going for the "bolt-ons" like these first thing......of course!! Hope this helps somebody out there!
 

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I'm having the same problem with the service trailer brake message but the ABS light also comes on intermittenly. I just got the truck about a week ago but it was not happening until I switched the hankook 285s for hankook 265s yeaterday. I do know that one of the tire pressor sensors is not working. .....
 

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same problem fixed

I've had the same problem for over a year but since I wasn't towing I didn't worry. My truck (08 2500HD duramax) was going to go off warranty soon so I had the dealer look at it. The said a pressure sensor in the master cylinder that provides the voltage output based on pressures to the trailer brake control was dead. They replaced it and power bled the front brakes. No problems now.
The sensor part number is 1 15838718 if that helps anybody. Probably not a big deal to fix yourself if you can find the sensor. I see the one plug with wires on the master but I'm assuming that's the brake lights. Maybe that's the sensor instead.
 

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I'm having the same problem with the service trailer brake message but the ABS light also comes on intermittenly. I just got the truck about a week ago but it was not happening until I switched the hankook 285s for hankook 265s yeaterday. I do know that one of the tire pressor sensors is not working. .....
If you put 285's on without lifting the front end look at your wheel speed sensor wire. The tire may have rubbed against the UCA it and freyed the wire. It will give the ABS and trailer brake warning light. Happened to me when I did 285's and again with my lift when I did not tie the wire back far enough. Changed sensors and works fine.
 

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I've had the same problem for over a year but since I wasn't towing I didn't worry. My truck (08 2500HD duramax) was going to go off warranty soon so I had the dealer look at it. The said a pressure sensor in the master cylinder that provides the voltage output based on pressures to the trailer brake control was dead. They replaced it and power bled the front brakes. No problems now.
The sensor part number is 1 15838718 if that helps anybody. Probably not a big deal to fix yourself if you can find the sensor. I see the one plug with wires on the master but I'm assuming that's the brake lights. Maybe that's the sensor instead.
It is on the bottom side. I had the same problem with my 08 but with mine the trailer had not brakes. The dealer replaced the sensor and as you said, they have a cool new system to bleed the brakes and it also made my brake pedal feel a LOT better than before after they did it. Weird thing was on trailers I ran 3.5 on before, I had to adjust the brake controller to 6 or 6.5 afterward for the same amount of braking.
 

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How did you get them to do the update for free? Was it covered under warranty? My dealer wants to charge me 200 bucks to do the update
 

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I hooked up my fifth wheel and connected the brakes, hadn't made it out of neighborhood and had all kind of bells going off saying service trailer brakes, service brake system. I checked every easy connection then got under the trucks and disconnected the trailer brake wires at the connection box near the spare tire, water poured out of the connection. I hooked everything back together an haven't had another issue, that's been over a year. I may have shot myself in foot by saying that, will probably do it this week, lol. This probably won't work for everybody but seemed to be my culprit.
 

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Hey, I finally got my Rig fixed after replacing brake controller, brake switch and Harness all the way back to the 7 pin connector I still had the SERVICE TRAILER
BRAKE SYSTEM come up I dropped about 3k$ at 4 different shops telling me there theories ?but I took it to a different GMC dealer in Long beach told them what was replaced and that I had low voltage on the Trailer brake system and all it was is the trailer brake power was landed on the wrong terminal at the main ECU the trailer brake power was landed on the ignition switch terminal dealer did not charge me a dime and I am sure it was a manufacture defect from the factor. So! Before you change all other components first check the terminals on the Main board and make sure it's landed on the correct Termination point.
Light has not came up since and my trailer brakes are working perfectly fine!?
Thank you Long beach GMC in So Cal for taking the time to check everything and fixing the problem!
 
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