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2021 Sierra Trailer Brake Problems

Whip
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Whip Enthusiast

Whip

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I am still struggling trying to diagnose a problem with my trailer brake controller. My post is long, but I'm hoping someone with more knowledge than me might be able to deduce what is going on.  I have read about the issues with 2024 trucks when connected to a trailer with solar.  That sure sounds similar to what I've been experiencing, but doesn't seem like it applies to older trucks.  So I'm starting this thread from scratch.
 
Very sporadically while towing an RV I get the message "Check trailer wiring" followed immediately by "Trailer brakes connected". Sometimes it doesn't happen for a copulation hundred miles, and then will happen repeatedly ten times in a row before stopping again.
Twice I've gotten a message saying "Service trailer brake system". When this battlements I lose the trailer brakes entirely and find that the fuse for the trailer brakes is blown. I replace the fuse and everything works again for awhile.
 
I towed a different trailer that did not have trailer brakes and with that one I got the "Check trailer wiring" message and found that I had lost the rear running lights and side marker lights. After unplugging, reconnecting and restarting the truck they were back on.
 
I have replaced the trailer brake controller located above the spare tire and also the trailer connector plug in on the truck.
My truck is a 2021 GMC Sierra 2500 HD.
 
I'm at a loss on what to try next or how to diagnose this.  Any help is appreciated!
  • 8 months later...
Whip Enthusiast

Whip

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I had forgotten about this post from last spring and thought I would post a follow-up for anyone who might come across it.  My trailer brake issue turned out to be a problem with a worn wire inside the axle on the trailer, and nothing to do with the truck itself. Intermittent wiring problems are so tough to diagnose and track down, so we were trying as many different things as we could come up with. Wish we had guessed right in the first place, but happy to have finally figured it out.

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bruceb58 Enthusiast

bruceb58

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Posted (edited)
On 12/27/2024 at 6:24 AM, Whip said:

I had forgotten about this post from last spring and thought I would post a follow-up for anyone who might come across it.  My trailer brake issue turned out to be a problem with a worn wire inside the axle on the trailer, and nothing to do with the truck itself. Intermittent wiring problems are so tough to diagnose and track down, so we were trying as many different things as we could come up with. Wish we had guessed right in the first place, but happy to have finally figured it out.

I got rid of my electric brakes, but before I did,  I was close to being proactive and doing homeruns for the wires from each wheel to a junction box. The way trailer manufacturers daisy chain the brake wires just sucks to troubleshoot. You can do a resistance measurement and get a somewhat good idea if all the magnets are in the chain but way easier if you can take one off at a time at a junction box.

Edited by bruceb58

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