[GMCHank]

Update:
I want to update my original post concerning 2024 Duramax 3500 Denali Crew Cab long wheel bed. This is an issue with GMC 2024 and 2025 HD models. The issue is the truck disconnecting my 17,000 lb 39ft 5th wheel's (DRV Mobile Suites) when you are traveling on the road. This appears to be a common problem with any trailer that has a power source i.e. battery, solar. The brakes are electric over hydraulic made by Hydrastar. After 3 months of going back and forth with GM, installing the recall fix for this problem which did not work. I met with engineer from GM, GM regional Service Mgr., dealership Shop foremen and Service Director at my dealership.

This meeting finally came up with a solution. A part that can be purchased from Hydrastar for $50.00 (part #381-7074). I spoke with the Hydrastars owner and chief electrical engineer, Wendell, for 45 minutes. He pulled no punches and is very frustrated with GM after dealing with them over this issue. One issue is the replacement part for the GM recall is not going to work. I had the recalled part installed so I can verify it is not going to work. Five miles down the road trailer brake disconnect warning light came on. Put the 5th wheel back in storage and back to the dealership and then replaced the wiring harness for the 7-pin outlet in the bed and it did not work.

Hydrastar is very confident this part will fix the problem. After splicing this part on to Hydrastar’s brake wiring, I took the trailer out for over 25 miles without the trailer brakes disconnecting We are going to increase our milage gradually since we have been burned 4 different times with this dangerous issue. It appears that GM is not accepting any responsibility over this issue.

What bothers me is that GM is aware of this problem, and it appears that GM is trying to blame everyone else but GM. If it wasn’t such a Dangerous issue I would not be so concerned. I have had an issue with my brand new 2020 which is the exact truck configuration as this 2024. I traded in a 2017 GMC Duramax with the same configuration (never any problem with 2017) and first time we went to leave with 5th wheel and the new 2020 GMC Duramax 3500 it was not compatible with lights and brakes. Two 1/2 months later and again having to get GM engineer down to TX, he brings an LED electrical adapter with him made by Curt part# 57003 which lets truck recognize trailer LED lights. GM was aware of this problem but ran us around for over 2 months and we could not use the 5th wheel.

I have had it with GM. I don’t say this lightly, but I will never buy another GM product again and I have never had anything but GM products all my life. Just in the last 7 years I bought 4 GMC vehicles.. I know no truck is perfect, but these problems are too dangerous to ignore

I had the same problem with my 2024 GMC 3500 this past summer. The dealership replaced the module and it did not help. I finally managed to speak with Wendell at HydraStar, got the diode, installed it on my fifth wheel and the problem was immediately remedied. 2 weeks later I went from IL to CO and back and not one error message. I didn’t have the problem with my 2022 GMC with the same fifth wheel trailer so GM obviously changed something. I don’t think that it had anything to do with the solar, it’s definitely the EOH brakes. Wendell at HydraStar is great. GM, not so much.

 

[Mtu Alum]

The trailer brake power module changed due to chip shortage. While the same specs were used, things are not always created equal.

The hydrastar fault and solar panel fault were both setting the same trouble code. There was a service bulletin telling dealers to replace module with this particular trouble code.

The hydrastar fault was hard to find and reproduce. It was somewhat dependent on driving style with applying the trucks brakes. After capturing data on it, hydrastar was providing some feedback through the electrical connection that other EOH suppliers don't.

GM worked with Hydrastar to supply a fix that could be quickly purchased. GM is working a fix but circuit board redesign takes longer then it would be acceptable. Sometimes things are as easy as they seem.

 

[Pjrnor78]

We have been going through this issue since early January. We had our 2024 Chev Silverado 2500 HD diesel in for service for the trailer brakes disconnected/connected/service trailer brake messages. After 3 days at dealer they couldn’t find anything. We already had the brake controller changed due to recall. We left the RV Park thinking it was fixed and about 50 miles out it did it again. We did disconnect the solar panel, but that didn’t help.
As we drove into our RV site at the next RV Park, (we are on a cross country 8 month trip) about 120 miles out, our left brakes seized.
RV Mobile mechanics said brakes and drum were shot and crumbling. They also checked the truck and it showed a faulty connector on the truck. We took it into the local Chev dealer and they found a faulty trailer brake switch and put a new one in. Today we were researching any NHTSA issues other than the recall of the controller and found NHTSA Bulletin No. 21-NA-155. This is about the possible cause to what we experienced. It references a manufacturer recommendation to make sure the correct OEM Pollak 7 way (trailer side) is installed part 12-706 or 12-702. Our trailer is only 2 months old and has Epicord 7 way.
The mobile mechanics are coming next week to install new brakes and drum along with installing the Pollak 7 way trailer plug.
GM was supposed to make sure this was communicated to service depts and customers.
We, too, plan to test drive before we drive any distance. We have been stranded here for 3 weeks but lucky this didn’t happen on the interstate. If we get the message again we are buying a RAM. This is maddening! We are planning to submit a complaint to NHTSA, Chevrolet and Alliance (RV).
I’ll post an update next week.

 

[btrussell1]

I had the same problem with my 2024 GMC 3500 this past summer. The dealership replaced the module and it did not help. I finally managed to speak with Wendell at HydraStar, got the diode, installed it on my fifth wheel and the problem was immediately remedied. 2 weeks later I went from IL to CO and back and not one error message. I didn’t have the problem with my 2022 GMC with the same fifth wheel trailer so GM obviously changed something. I don’t think that it had anything to do with the solar, it’s definitely the EOH brakes. Wendell at HydraStar is great. GM, not so much.

We've been researching our brake seizing issue for about a month and this thread popped up. We are driving a 2023 GMC Sierra 1500, and was towing our 2023 Basecamp 20X (solar onboard) to the dealer for some unrelated repairs. Absolutely NO WARNING from the brake controller/trailering system when our brakes caught and burned completely up. We dropped the Airstream off and next day went to GMC. They found a burned 20 amp fuse out, and gave us the aforementioned service bulletins. But, now I'm thinking, why would the systems be any different on a GMC truck regardless of the make/model. Worth a try to get this resolved before this issue kills us. How do we reach HydraStar? (New to this forum.)

 

[GMCHank]

We've been researching our brake seizing issue for about a month and this thread popped up. We are driving a 2023 GMC Sierra 1500, and was towing our 2023 Basecamp 20X (solar onboard) to the dealer for some unrelated repairs. Absolutely NO WARNING from the brake controller/trailering system when our brakes caught and burned completely up. We dropped the Airstream off and next day went to GMC. They found a burned 20 amp fuse out, and gave us the aforementioned service bulletins. But, now I'm thinking, why would the systems be any different on a GMC truck regardless of the make/model. Worth a try to get this resolved before this issue kills us. How do we reach HydraStar? (New to this forum.)

 

[Allen B]

We've been researching our brake seizing issue for about a month and this thread popped up. We are driving a 2023 GMC Sierra 1500, and was towing our 2023 Basecamp 20X (solar onboard) to the dealer for some unrelated repairs. Absolutely NO WARNING from the brake controller/trailering system when our brakes caught and burned completely up. We dropped the Airstream off and next day went to GMC. They found a burned 20 amp fuse out, and gave us the aforementioned service bulletins. But, now I'm thinking, why would the systems be any different on a GMC truck regardless of the make/model. Worth a try to get this resolved before this issue kills us. How do we reach HydraStar? (New to this forum.)

This meeting finally came up with a solution. A part that can be purchased from Hydrastar for $50.00 (part #381-7074). I spoke with the Hydrastars owner and chief electrical engineer, Wendell, for 45 minutes. He pulled no punches and is very frustrated with GM after dealing with them over this issue. One issue is the replacement part for the GM recall is not going to work. I had the recalled part installed so I can verify it is not going to work. Five miles down the road trailer brake disconnect warning light came on. Put the 5th wheel back in storage and back to the dealership and then replaced the wiring harness for the 7-pin outlet in the bed and it did not work.
This meeting finally came up with a solution. A part that can be purchased from Hydrastar for $50.00 (part #381-7074). I spoke with the Hydrastars owner and chief electrical engineer, Wendell, for 45 minutes. He pulled no punches and is very frustrated with GM after dealing with them over this issue. One issue is the replacement part for the GM recall is not going to work. I had the recalled part installed so I can verify it is not going to work. Five miles down the road trailer brake disconnect warning light came on. Put the 5th wheel back in storage and back to the dealership and then replaced the wiring harness for the 7-pin outlet in the bed and it did not work.
Phone 812-655-4544

 

[Mtu Alum]

T

We've been researching our brake seizing issue for about a month and this thread popped up. We are driving a 2023 GMC Sierra 1500, and was towing our 2023 Basecamp 20X (solar onboard) to the dealer for some unrelated repairs. Absolutely NO WARNING from the brake controller/trailering system when our brakes caught and burned completely up. We dropped the Airstream off and next day went to GMC. They found a burned 20 amp fuse out, and gave us the aforementioned service bulletins. But, now I'm thinking, why would the systems be any different on a GMC truck regardless of the make/model. Worth a try to get this resolved before this issue kills us. How do we reach HydraStar? (New to this forum.)

Putting the diode in won't hurt anything but, I'm not totally confident it will fix your issue. The 2023 didn't have the problems that the 2024 did. The 2024 problems were trailer brakes not working vs your problem.

#iworkforGM

 

[hehemtp]

So in reality, if you have 2024 GM HD truck and Hydrastar EOH on trailer, you need the fix for the brake wire installed on trailer and if you have solar on trailer, you may need a solution for the 12v power line. I have a 2023 and trailer has solar (only 45watt) and have not noticed a problem, but was aware that I may have to do something to keep solar charging from feeding back to truck causing an error.

I had an external brake module installed and bypassed the on board controller works great. Gm not taking responsibility so the Attorney are doing there thing.

 

[Allen B]

This meeting finally came up with a solution. A part that can be purchased from Hydrastar for $50.00 (part #381-7074). I spoke with the Hydrastars owner and chief electrical engineer, Wendell, for 45 minutes. He pulled no punches and is very frustrated with GM after dealing with them over this issue. One issue is the replacement part for the GM recall is not going to work. I had the recalled part installed so I can verify it is not going to work. Five miles down the road trailer brake disconnect warning light came on. Put the 5th wheel back in storage and back to the dealership and then replaced the wiring harness for the 7-pin outlet in the bed and it did not work.
This meeting finally came up with a solution. A part that can be purchased from Hydrastar for $50.00 (part #381-7074). I spoke with the Hydrastars owner and chief electrical engineer, Wendell, for 45 minutes. He pulled no punches and is very frustrated with GM after dealing with them over this issue. One issue is the replacement part for the GM recall is not going to work. I had the recalled part installed so I can verify it is not going to work. Five miles down the road trailer brake disconnect warning light came on. Put the 5th wheel back in storage and back to the dealership and then replaced the wiring harness for the 7-pin outlet in the bed and it did not work.
Phone 812-655-4544

This will be my last update because I have solved the problem of my GMC 3500 Duramax disconnecting my trailer brakes on our 39 ft 5th Wheel. After jumping through all the hoops to fix this extremely serious problem including going through recall to fix this disconnect issue and it not working. Going through the process with GM to buy our truck back, which was suggested by our dealership, considering dealer is not at fault but they wanted GM to pick up some of the loss on buying back truck, we thought to give it a try, No success.
We solved the issue by buying, our first, brand new 2024 F350 Platinum 6.7 High Output Power Stroke Platinum and yes we took a hit. What made me even madder was when setting up truck for towing i.e. length, weight etc. there is a tab labeled brakes. You had 2 options for brakes one which is "hydraulic over electric brakes". This is the problem with the 24 and 25 GM HD trucks and which GM can't or won't fix. Ford has a solution on their trucks already built into their Super Duty's and do not try to deflect blame on to the trailer manufactures.

I have had it with GM products and that is after us buying 4 new GM vehicles in 7 years adios.

 

[Allen B]

Is it only HydraStar EOH that have the problem?

I can't answer this exactly, but with Ford having "hydraulic over electric " on their trailer set up screen it appears this is an industry wide use on 5th wheels. The bigger issue I think is that GM knows the issue is there and I don't need to hear it takes longer to fix than expected. The bottom line is this is a tremendous safety issue which has been addressed by Ford but GM can't or won't even acknowledge the problem exists!

 

[SNadler]

Well I hate to say this but I have a 2025 Silverado 3500HD and just returned from Pigeon Forge to High Springs Florida and trailer brakes stopped working 4 times. Each time i had to unplug the 7 pin and reconnect it to get trailer brakes to work. Not sure if Ill get the runaround or not at GM but I have an appointment next week. I do have solar and Lithium

 

[Mtu Alum]

Well I hate to say this but I have a 2025 Silverado 3500HD and just returned from Pigeon Forge to High Springs Florida and trailer brakes stopped working 4 times. Each time i had to unplug the 7 pin and reconnect it to get trailer brakes to work. Not sure if Ill get the runaround or not at GM but I have an appointment next week. I do have solar and Lithium

Which trailer brake system do you have?

 

[Allen B]

The best that I can figure out having dealt with this situation for a year and a 1/2 is if you have a power source. I e battery or solar on your trailer with hydraulic over electric brakes you're going to have problems. I have stayed out of this recently because the way I solved, the issue is that I did install the diode from, the brake manufacturer of my fifth wheel and it appeared that it worked but I got so disgusted with GM who will not stand behind their product with this serious issue. I traded my 2024 HD with twelve thousand miles and for a brand new Ford F350 and have had no trailer issues.

 

[vfalcon7]

just installed the diode from Hydrastar after spending 3 hours at dealer only to tell me the part I need to order.... The well right know what is going on they gave me the print out with part number and how to splice it in. Allen above did it to his truck before trading it in it looks like. I will be using my truck and trailer Thursday and will report back.

 

[Busa Dave]

Had my 24 ZR2 in last week for a tranny service, trans case fluid change and a fuel filter and they found this issue on the computer and replaced the module.

 

[mpouls1]

I have a 2021 3500 LT Duramax that will do this intermittently, not all the time while towing, but does happen occasionally. My TT weighs 5100 pounds fully loaded so it's not as much of a concern like others towing much heavier but now it's got me thinking. The message on DIC says "Trailer Brake Disconnected " even though I didn't do anything.

Time to more research especially if I buy a heavier camper, which I was looking to do earlier this year, but didn't pull the trigger.

 

[vfalcon7]

Used my truck and trailer yesterday after installing Hydrastar Diode fix. Worked like a charm not one message popped up and trailer brakes worked as they should. Towing a 12000# boat and trailer.

 

[Noe911]

That seems to be the fix for everyone, unless your truck is under warranty and you can get the dealership to change it out like I did.

 

[vfalcon7]

yes my truck is a 2025 with only 9k for miles. They will change it out? I spent 3 hours at deanship and they sent me home with a page printed out with the diode to BUY!!!

 

[Noe911]

That’s insane! I pretty much had to twist the service manager‘s arm and let him know when I ran into the problem with 4000 miles on my 2024 Denali and said this is a GMC major F up and it needs to be corrected by General motors!