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Old 06-23-2024, 03:03 PM   #1
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Sutton , Ontario
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My trailer will not work with a GMC

I am towing a 30rbt with an F150. Everything works perfect.

When I hook it up to my son's GMC 3500 the brakes work roughly 50% of the time. On the other 50% I get an error on the GMC dashboard telling me to check the wiring and the brakes do not work. The lights, signals, and brake lights work all the time.

The first thought is that there is a problem with the GMC but the GMC works perfectly when towing his fifth wheel trailer which also uses a 7 pin connector.

Anybody had anything similar happen?
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Old 06-23-2024, 03:25 PM   #2
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My first thought is that there's some electrical characteristic of your brake wiring that the Ford tolerates and the GMC does not. If, when you apply the brakes with the Ford (or pull the breakaway) all 4 wheels exhibit enough magnetic force to swing a compass needle toward them at roughly the same distance from the wheel, you have some evidence that all 4 brakes are electrically similar (there can be mechanical differences but the brake circuit shouldn't be able to detect those.)

Do you have solar panels on your trailer? I came across a post about Chevrolet HD trucks not liking the higher voltage they were "seeing" from the trailer battery: Chevy Silverado trailer brake disconnect

I recently read another post about an integrated brake controller disconnecting from the brakes but putting an aftermarket controller in the braking circuit worked fine... I didn't find that post when I searched just now but if memory serves, their problem was a bad trailer battery causing some sort of voltage problem the integrated brake controller didn't like and the aftermarket controller just shrugged off.
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Old 06-24-2024, 06:54 AM   #3
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Does your trailer have lithium batteries and or solar panels? Either one can make the trailer battery voltage higher than what the brake controller expects to see. There is a service bulletin from GMC on this. A replacement brake controller from GMC usually. takes care of this.
I have a 2024 Chevrolet 2500 and tow our Airstream with solar and lithium batteries. I installed a dc/dc charger and have had no issues with the brake controller.
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Old 06-24-2024, 09:25 AM   #4
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With the Ford it appears that everything is working perfectly, but is it?

The GMC throws an error about half the time. Perhaps the Ford is also encountering the same problem but just doesn't throw error messages?

My initial thought is that perhaps your trailer's brakes are only working half the time. The GMC knows this, but the Ford is blissfully ignorant of it.

Worth doing a thorough inspection of the trailer's brake wiring to look for breaks, shorts, etc. Give every connection a tug, and look carefully for splits, breaks, or rubbed spots on the insulation.
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Old 06-24-2024, 10:13 AM   #5
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Check your Trailer connector! For some reason Airstream uses Bargman (?) 7 pin connector on the trailer pig tail. These double contact ("duck-bill") connectors do not meet the SAE Standards and DO NOT play well with most of the OEM 7 pin sockets that meet the SAE Standard.

Here is a bulletin that RAM put out
--- https://www.ramtrucks.com/BodyBuilde...2BI1n%2Bn9n%0A

I switched my truck to a Pollak 12-706 and all messages about trailer brake disconnected and intermittent problems went away. These Pollak connectors are less than $8 on Amazon and it only takes a few minutes to cut the old one off and wire up the new one.

I hope that helps

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Old 06-24-2024, 10:52 AM   #6
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Many GMC's have a 2nd 7-pin connector in the bed for 5th wheels, as well as the one on the receiver hitch. If you son is using the bed receiver and you are using the hitch receiver that could account for the problem, as it's two separate sets of wiring. Could be a bent pin, loose wire, etc...

If your whip is long enough you could try to connect to the bed receiver and narrow it down that way. But as far as towing an airstream with a GMC, my '21 3500 doesn't throw codes so I don't think there is a deeper GMC / Airstream incompatibility.

That said, I also have lithium, solar, and a DC to DC charger like the other person who responded so if you do as well, and the truck isn't set up with DC to DC it could be the issue they noted.

Good Luck!
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Old 06-24-2024, 12:47 PM   #7
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Quote:
Originally Posted by Dan_Rox View Post
Does your trailer have lithium batteries and or solar panels? Either one can make the trailer battery voltage higher than what the brake controller expects to see. There is a service bulletin from GMC on this. A replacement brake controller from GMC usually. takes care of this.
I have a 2024 Chevrolet 2500 and tow our Airstream with solar and lithium batteries. I installed a dc/dc charger and have had no issues with the brake controller.
Good point. I recently had the brake controller on my GMC 2500HD replaced by GM in response to that service bulletin. I hadn't yet experienced the problem, which can occur if the solar controller charges the trailer batteries to a higher voltage than the truck battery, but my dealer agreed that waiting for a failure to occur in a critical situation was not the best approach.
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Old 06-24-2024, 12:55 PM   #8
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When we changed to an new tow vehicle in 2022, it mostly did not recognize that our trailer was attached. Our trailer had incandescent bulbs in the running and other exterior lights. They have greater resistance than LED lights and, apparently, the vehicle "thought" something was wrong. We changed all of the exterior lights to LED and the problem disappeared.

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Old 06-24-2024, 02:48 PM   #9
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I pull a 2008 Classic that has electric over hydraulic brakes. I’ve never been able to make the trailer brakes work with a GM, but they work fine with Ford. Ford offers a choice in the control panel to select e/h brakes, GM doesn’t. The GM dealer suggested I add a brake controller to their truck to fix the problem. Maybe yes, maybe no.
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Old 06-28-2024, 07:26 PM   #10
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For reference, I started this thread.

I took my truck into GM last Tuesday. I told them about the service bulletin regarding 2024 3500 trucks and the brake controller problem. They looked it up and replaced the controller with a replacement specified by GM.

I took the trailer out for a 2 hr. drive today and didn't have 1 problem. Prior to the repair, I couldn't even get out of the driveway without an error message re the brakes.
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Old 06-28-2024, 07:28 PM   #11
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Thanks to DKB-SATX for pointing to toward the repair.

Gary
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Old 07-07-2024, 10:29 AM   #12
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Quote:
Originally Posted by Garyasml View Post
I am towing a 30rbt with an F150. Everything works perfect.

When I hook it up to my son's GMC 3500 the brakes work roughly 50% of the time. On the other 50% I get an error on the GMC dashboard telling me to check the wiring and the brakes do not work. The lights, signals, and brake lights work all the time.

The first thought is that there is a problem with the GMC but the GMC works perfectly when towing his fifth wheel trailer which also uses a 7 pin connector.

Anybody had anything similar happen?
Fwiw, my 2021 2500hd has no issue braking my 30’ Classic. I have solar and lithium. Imho get the trucks brake module lchecked.
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Old 07-07-2024, 01:32 PM   #13
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I'm not sure what year the GMC is or if the trailer has solar? We have a 2023 Flying Cloud with 300W solar and a 2024 GMC 2500 Denali HD. I used to experience similar issues and it turns out the GMC integrated brake controller has an issue when the trailer battery voltage would become higher than the truck voltage at the connector. This higher voltage in the trailer would cause a false indication that the connector had become disconnected and the brakes would not work. The brakes actually still work and the connector was still connected. Turns out GMC has a service bulletin out (Bulletin #23-NA-149) and the brake controller board must be swapped out with a later revision to correct the problem. We had our brake controller card swapped under warranty and have not had the issue since and all works great.
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Old 07-07-2024, 03:33 PM   #14
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Quote:
Originally Posted by Garyasml View Post
For reference, I started this thread.

I took my truck into GM last Tuesday. I told them about the service bulletin regarding 2024 3500 trucks and the brake controller problem. They looked it up and replaced the controller with a replacement specified by GM.

I took the trailer out for a 2 hr. drive today and didn't have 1 problem. Prior to the repair, I couldn't even get out of the driveway without an error message re the brakes.
I just purchased a 2024 GM HD. Do you happen to know the specific service bulletin? Thanks for this thread.
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Old 07-07-2024, 04:22 PM   #15
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Originally Posted by Jason P M View Post
I just purchased a 2024 GM HD. Do you happen to know the specific service bulletin? Thanks for this thread.
I believe it is TSB #23-NA-149.

The part number for the replacement module is 85073615.

I also had this repair done under warranty.
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Old 07-07-2024, 11:17 PM   #16
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Quote:
Originally Posted by mikeinca View Post
I believe it is TSB #23-NA-149.

The part number for the replacement module is 85073615.

I also had this repair done under warranty.
Thank you!
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Old 01-19-2025, 10:03 PM   #17
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More than just the pickups?

I just bought a new Duramax Yukon XL with max towing package and when I hooked up my 1976 Airstream Overlander and was amazed at the "self-check" features of the towing software... until I got about 30' feet and a "check trailer brakes" and "no gain" detected. Worked with my previous (but older) Suburbans -- I think I'll take this infor (SB and part number) and see if that's my problem too -- any other observations??
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Old 01-20-2025, 07:22 AM   #18
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Brakes

Quote:
Originally Posted by OilnH2o View Post
I just bought a new Duramax Yukon XL with max towing package and when I hooked up my 1976 Airstream Overlander and was amazed at the "self-check" features of the towing software... until I got about 30' feet and a "check trailer brakes" and "no gain" detected. Worked with my previous (but older) Suburbans -- I think I'll take this infor (SB and part number) and see if that's my problem too -- any other observations??
Since its an older AS, imho, you got a magnet or brake wiring problem. These new systems are tons more sensitive.
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Old 01-20-2025, 10:24 AM   #19
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I took my Sport/Bambi out for a quick trip just after getting the "new to us" 2023 3500 LTZ and it worked great. I have solar and lithium. I have never relied on the truck to charge the battery so if it turns out to be a problem I will just disconnect the 12 V charging lead from the 7 pin plug.

We ran around town for an hour in all sorts of stop and go traffic and no messages popped up and the trailer brakes did what they are supposed to do.

I did have the battery switched off inside the trailer and the solar panels turned off as well.
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Old 01-20-2025, 02:41 PM   #20
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Two things to check:
First, the 7way plug on your trailer, this very well could be the problem as some others have suggested.
Second, Does your airstream have hydraulic brakes? If so GM's have an issue with these as the brake controller is looking for a load and with hydraulic you don't have the load like you do with electric. There are kits out there that install on the camper side that 'tricks' the controller allowing it to work correctly.

Good Luck..
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