2019 Transcend 27BHS Brakes Don’t Function with New GMC

[JeepWis]

I have a 2019 Transcend 27 BHS trailer that I used to tow with a 2015 Chevy Silverado 1500 with a factory brake controller and everything worked perfectly fine. I recently bought a 2022 GMC Sierra 1500 with a factory brake controller and my trailer brakes work for a few minutes and then I get an error on the dash that says “Trailer Brakes Disabled, Service Trailer Brake System.” I took the truck into the dealer and everything checked out fine. I read it could be due to a bad connection at the plug, so I bought a new trailer plug, installed it, and it didn’t fix the brake issue. I have full trailer light functionality as well. Any help or recommendations would be helpful. Thanks!

[familytruckster4]

The fault is most likely in the trailer assuming the dealer tech did exactly what he was supposed to in the diagnosis. The electronics on the truck are complex and nothing like they used to be. The truck will detect a fault in the trailer that never would have showed up on previous models. The new trucks are super sensitive to ground issues. If you have any more specific info on the failure send me a PM, I have an insider I can run it by for you.

Scott

[Guest]

The fault is most likely in the trailer assuming the dealer tech did exactly what he was supposed to in the diagnosis. The electronics on the truck are complex and nothing like they used to be. The truck will detect a fault in the trailer that never would have showed up on previous models. The new trucks are super sensitive to ground issues. If you have any more specific info on the failure send me a PM, I have an insider I can run it by for you.

Scott

Agree with Scott.

The dealer has a plug in unit (if they used one) that will check the circuits and functionality at the 7 way plug on the truck side. The truck itself can also diagnose the trailer. It would be nice if they had a tool to plug into the trailer which would no doubt reduce warranty claims. Anyone looking for a patent?

Update: The replacement plug must be a Pollak plug and no other.

Jim

[familytruckster4]

GM and likely Ford also, have been spending a lot of diag time on trucks when in fact the junky trailer wiring is almost always the culprit.

[JeepWis]

Awesome, thanks guys, super helpful! I’ll do some diagnostics on the trailer wiring.

[Jlawles2]

JeepWis I suggest you start with the ground (negative) circuit of the system as mentioned by Scott. Lights will back feed through each other (may cause strange lighting issues) and are not a "good" way to determine if the trailer wiring is truly OK.

I also suggest that you check the brake wires where they go into the axle tubes and if you have not serviced or have just recently serviced or had serviced the axle hubs, verify that there are no wiring issues in there. Any short in the wiring to the magnets will trip the brake controller into fault. I pulled a car hauler with torsion axles that had a rubbed wire on the magnet. Created HAVOC trying to figure out when the brakes would or would not work as it was intermittent.

[familytruckster4]

JeepWis check your PM's

[Country Campers]

Follow the 7 plug back to the box on the trailer frame, a nice silver box, inside you will find a nice mess of wires with possibly a loose ground connection or even a brake wire loose. You may even want to check the wiring back at the wheels to make sure that they are correct.

Brian

[JeepWis]

I cleaned up the grounds from the 7 pin today and checked them going back to the axles. Problem is still there. I think I’m going to pull the wheels off tomorrow, and see what’s going on inside the drums. Thanks again guys!

[Country Campers]

JeepWis

In your picture the group of white wires that are taped up are all the grounds connected in one bundle. Is there a wire nut holding these together or is it just taped? This is a good place to make sure all grounds are good. If you have a magnetic compass you could hold it near the lower part of the tire rim and have someone push the brake pedal in the truck, the pointer on the compass should point towards the wheel if the brake magnet is getting energized, make sure that the point is not pointing towards the wheel before testing this ( trust me on this). If the pointer does not move then you may not have proper power going to the brakes, check all of the brakes. This just save a little work from pulling the wheels if there is no need to.

Brian

[JeepWis]

Hey Brian,

The 4 grounds under the black electrical tape go into a large wire nut. I took it off and they were all clean and seemed to be all connected. I cut the ends off anyway, stripped the grounds a bit longer, and then put the wire nut back on and retaped it. I think I’d like to go to ring terminals and ground stud if I can’t find the problem.

Good idea on the compass. I’ll try that today!

Thanks,
Brent

[JeepWis]

Interesting bulletin I found from NHTSA.

https://static.nhtsa.gov/odi/tsbs/20...01177-9999.pdf

[familytruckster4]

Looks like you bought the correct plug when you got the Pollak.
I forgot to mention that if you need to replace the cord also it might be a good time to consider replacing your current junction box with one of these: https://www.etrailer.com/Accessories...EaApDVEALw_wcB

Or maybe the Pollak brand: https://tweetys.com/junction-box-7-t...4aAgtVEALw_wcB

You would also need some ring terminals to complete the job. When I did my fifth wheel I added a internal tooth lockwasher to each post for a good connection and then put dielectric grease on it. If you have to go that deep into it you might as well clean the mess of wiring up.

[Wileykid]

Although I would agree with everyone on the problem most likely being in the trailer, I would double check the trailer plug on the truck. I had a new 2016 Chevy 2500 that every so often would display the service trailer brake message. Hooked up a different truck, no message, take a trip with my truck, and after a couple hundred miles, would get it again, although I could reset it by turning the truck off and on. Couple of trips to the dealer, even with the trailer, and on the last one, had a sharp mechanic, when testing the truck said he would see some odd voltage numbers, but it did not trigger the testing machine. Tore the plug on the truck apart, and found that it had some corrosion, even though I was living in SoCal at the time. Replaced under warranty, filled with dielectric grease, and no further problems.

[TucsonJim]

Here is another data point that may weigh in your trouble-shooting. A few years ago, I decided to replace the brake lights on my 2017 Reflection travel trailer with LED bulbs vs. the original incandescent bulbs. They worked great for a while. But one day, while applying the brakes, I got a message on my Fords display that said "trailer brakes disabled". It was intermittent at first, then happened more frequently as time went on.

So I went through a ton of trouble-shooting to try and resolve it. I rewired all the grounds to a central buss terminal and replaced the 7way connector and junction box. I spent a ton of time trying to resolve the problem to no avail. Then it dawned on me. I remembered the LED lights. So I changed them back to incandescent. That was it, the problem never reappeared and the interaction between the truck and the trailer is still fine today. After much discussion, it was determined that the LED lights had much lower resistance than the incandescent bulbs. This tricked the truck into thinking there was a fault. There was nothing wrong with the truck, but it wasn't designed to accept the low resistance of LED bulbs.

This could be the issue with your combination also. If so, I believe there are resistors or adapters to help resolve the problem.

Jim