2015 sierra 3500 HD trailer brake relay - Chevy and GMC Duramax Diesel Forum
11-16 LML Performance Parts Discussion Discussion of Performance Parts For the 2011 to 2016 LML Duramax Trucks No Advertising

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post #1 of 15 (permalink) Old 01-27-2020, 09:50 AM Thread Starter
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2015 sierra 3500 HD trailer brake relay

Need to find a trailer brake relay for my 2015 GMC 3500HD. Getting the constant service trailer brakes when towing form my hitch. Replaced the dash switch, next up is the relay. Anyone know part number or where to grab a new one?
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post #2 of 15 (permalink) Old 01-27-2020, 10:11 AM
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Originally Posted by cincykid View Post
Need to find a trailer brake relay for my 2015 GMC 3500HD. Getting the constant service trailer brakes when towing form my hitch. Replaced the dash switch, next up is the relay. Anyone know part number or where to grab a new one?
You can find the correct part number by using your VIN# in the lookup process in lieu of the year, model, engine, etc. Works on most every GM-branded websites. Once you have the factory part number, you can shop for price and service anywhere you want. The relay is above the spare tire. I believe a picture of this was posted in the last week or so, do a search.

Ron Nielson
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post #3 of 15 (permalink) Old 01-27-2020, 11:56 AM Thread Starter
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When I do a search it shows part # 20904439 but if I search on a GM parts site with my vin, I cannot find a trailer brake relay and on the other sites it says that part number does not work on my 2015 gmc sierra 3500 HD denali. I figured as inexpensive as it was I would just replace it as I have already checked the trailer, the wiring connector from the trailer to the truck, and replaced the trailer brake controller in the dash.
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post #4 of 15 (permalink) Old 01-27-2020, 12:57 PM
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Looks like your mind is made up.

Ron Nielson
2008 Silverado LT, CCLB, Edge Insight CTS
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post #5 of 15 (permalink) Old 01-27-2020, 12:58 PM Thread Starter
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Im open to other suggestions. It is quite possibly one of the most annoying things I have to deal with when pulling (besides idiot drivers)
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post #6 of 15 (permalink) Old 01-27-2020, 05:31 PM
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I THINK the part number you are looking for is : 23337305. Not knowing the VIN# or particulars of your truck, I can't be absolutely sure.




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post #7 of 15 (permalink) Old 01-27-2020, 07:29 PM
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I don't have any idea what the part number is, but....
sometimes when an improved part is made available, it will have a new number, and GM's system will list the substituted number.

I'd walk into a dealer parts department with the VIN and get them to give price and availability. This should give you the latest part number.

If you think their price and delivery/availability is acceptable buy it from them. At some shops it might be in stock.

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post #8 of 15 (permalink) Old 01-28-2020, 04:07 AM Thread Starter
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I really appreciate all the help! Ron's part number shows it fits on my truck on Amazon. Found a factory replacement for $29. Hopefully it is also located above the spare tire on my 2015 and hopefully this solves the constant dinging on the dash when a trailer is connected! I really appreciate all the feedback! The only other issue I have ever had with this truck is the drivers seat vibration mechanism sometimes doesnt work for park assist/driver assist. I bought a new one but cannot for the life of me reach the clip on the side of the seat to pull it off to raise the drivers seat cushion to replace it. The clips on the under part front of the seat are easy, but the one on the side is behind the plastic piece that houses the controllers for moving the seat and I just cant get my fingers in there.
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post #9 of 15 (permalink) Old 01-28-2020, 05:13 AM
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Quote:
Originally Posted by cincykid View Post
Need to find a trailer brake relay for my 2015 GMC 3500HD. Getting the constant service trailer brakes when towing form my hitch. Replaced the dash switch, next up is the relay. Anyone know part number or where to grab a new one?
Quote:
Originally Posted by cincykid View Post
When I do a search it shows part # 20904439 but if I search on a GM parts site with my vin, I cannot find a trailer brake relay and on the other sites it says that part number does not work on my 2015 gmc sierra 3500 HD denali. I figured as inexpensive as it was I would just replace it as I have already checked the trailer, the wiring connector from the trailer to the truck, and replaced the trailer brake controller in the dash.
Have you tried other trailers, or this trailer on another truck?

I find it hard to believe that this is being caused by a relay. If a relay fails it will typically not close at all, which would lead to the truck not recognizing the trailer brakes as being connected (i.e., you'd never get the "trailer connected" message). I believe the "service trailer brake system" message is related to the resistance values across the trailer brakes not falling within the system's expected values, and the only way to check that directly is with an ohmmeter.

Rather than do a bunch of exploratory part replacement I would pick up one of these and see how your truck behaves with it. It's not cheap but the amount of time it will save you when diagnosing trailer wiring issues is more than worth the cost. Trust me.

In either case, the next thing I'd look at is the trailer brakes themselves. Take the brake drums off and inspect the internal parts and wiring to ensure there are no short circuits.

Good luck and let us know the outcome.
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post #10 of 15 (permalink) Old 01-28-2020, 05:50 AM
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Thanks for link to the tool to check trailer connector.

2012 3500hd srw 4 wd Jamco exhaust Kennedy dual lift pump Trifca bed cover B& W gooseneck hitch Western Diesel fuel filter relocation bracket
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