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2014 Silverado 2500hd lml
A couple of days ago started displaying "service trailer brake system" on the DIC. When hooked up to a trailer all lights and turn signals work. Just no power to the trailer brakes. I've replaced the trailer brake control relay above the spare tire. I've replaced the 30a stud 2 square fuse (slot 58) as well as the 20a blade fuse for itbc (slot 19) under the hood. NEITHER of the fuses were blown but replaced them anyway. I have disconnected and cleaned/air blown ALL of the connections at the rear of the truck leading to the 7 way rv plug. The Service Trailer Brake System" message continues to display. Any thoughts or ideas? Does the ITBC module (gm part 20964299) next to the itbc relay give trouble or go out often? I've also disconnected it and cleaned its large block connection. Help much appreciated.
 

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I'd be looking at the trailer. So so many reports like this end up being some crummy trailer wiring.....

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Discussion Starter #6
This is definitely a truck problem. It started when the vehicle wasn't hooked up to a trailer and continues to display even after the batteries have been disconnected/reconnected, and it is still not connected to a trailer.
 

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This is definitely a truck problem. It started when the vehicle wasn't hooked up to a trailer and continues to display even after the batteries have been disconnected/reconnected, and it is still not connected to a trailer.
If that was in there, I missed it. My bad.

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2014 Silverado 2500hd lml
A couple of days ago started displaying "service trailer brake system" on the DIC. When hooked up to a trailer all lights and turn signals work. Just no power to the trailer brakes. I've replaced the trailer brake control relay above the spare tire. I've replaced the 30a stud 2 square fuse (slot 58) as well as the 20a blade fuse for itbc (slot 19) under the hood. NEITHER of the fuses were blown but replaced them anyway. I have disconnected and cleaned/air blown ALL of the connections at the rear of the truck leading to the 7 way rv plug. The Service Trailer Brake System" message continues to display. Any thoughts or ideas? Does the ITBC module (gm part 20964299) next to the itbc relay give trouble or go out often? I've also disconnected it and cleaned its large block connection. Help much appreciated.
my 2008 3500hd did the same thing while I was at the diesel pump filling up an pulled out on the road with the trailer went home unhooked the trailer an the next 5 days every time I started it an drove it it said service trailer brake system took it to the shop they ran a code reader found out it was a wheel sensor not working but it could only be read with the scanner they had my stupid code reader would say no codes found $300 peace of junk ...they replace the wheel ABS sensor an it went away, good luck with it but if you must take it to a shop ...have them do a code an see if they will tell you what its is an maybe you could do it yourself an cost only the code reading. then you can buy the part an do it your self...from what I understand the code is in a computer that code reader do not look at like body computer an transmission computer not sure what the reader looks at but they told the reader they have cost over 3K an can do stuff mine will never do
 

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A reader that will read 'C' codes(Miscellaneous codes) will tell you about wheel speed sensors. OReillys Auto Parts stores have very nice Bosch scanners that will read these codes and they will do it for you for free. I use Blue Driver ($100) and it reads most everything except airbag and TPS systems for my 2008 truck and it works a wide variety of makes and models, including my Mercedes.
 

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I had a similar problem several years back with my 2500HD and an eighteen foot open car trailer. The dealership replaced the seven pin plug at the rear of the truck under warranty. That didn't fix the issue. I later discovered the electric brake wire on the driver's side of the car trailer was being pinched by the leaf springs. Thus, the wire was shorting out. I'm in the process of rewiring everything on the car trailer.
 

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A reader that will read 'C' codes(Miscellaneous codes) will tell you about wheel speed sensors. OReillys Auto Parts stores have very nice Bosch scanners that will read these codes and they will do it for you for free. I use Blue Driver ($100) and it reads most everything except airbag and TPS systems for my 2008 truck and it works a wide variety of makes and models, including my Mercedes.
Thanks for the tip on the blue driver. Might have to get one. Always looking for a GOOD scan tool.

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I don't intend to say that Blue Driver is the tool of choice. You need to assess your particular vehicle(s) and situation before deciding. Another unit that I have been looking at is Thinkcar. One of the advantages of this is that it offers 2 way interactive controlls and automated ABS brake bleeding. But look around before deciding on any particular scanner.
 

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I don't intend to say that Blue Driver is the tool of choice. You need to assess your particular vehicle(s) and situation before deciding. Another unit that I have been looking at is Thinkcar. One of the advantages of this is that it offers 2 way interactive controlls and automated ABS brake bleeding. But look around before deciding on any particular scanner.
Dang. That's entertaining too..


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I sometimes get that “service trailer break system”. Ive seen it pop up like 3 or 4 times within the last year.
All my lights and trailer breaks worked ok.. 7 pin plug was also nice and snug. No loose connections.

The top spring loaded cover on the 7 pin was loose, so I believe it kept the plug from staying snug in place while on the road or big bumps.
 
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