Factory brake controller not working new 2020 gmc yukon

[stevemedic]

I recently replaced my 2016 Yukon XL with exact 2020 model/trim. Both had the GMC factory built in break controller. In the fall I put my 2019 Rockwood Roo 233S in storage with the 2016, never had an issue with the break controller or brakes on the camper. A few weeks ago I went to take my camper out of storage with my 2020 and when I hooked up the 7 pin plug form trailer to my new vehicle, everything worked, lights, etc.. except my new vehicle would not recognize that the electric brakes were connected. I tried cleaning both sets of terminals, reseating, followed the wiring etc.. still would not show as connected with my new vehicle on the dash.

Luckily I didn't have to tow it home very far and very little traffic.

Am I missing something simple? If i do have an issue that would need servicing or repair, how do I determine if the fault is with my new vehicle, or a problem with the trailer connection end?

Thanks

[babock]

Measure the 7 pin connector from the brake pin to ground with an ohmmeter on the trailer side. Should be around 1 ohm.

[Bama Rambler]

Does the DIC show any errors when you plug the 7-way into the truck?

When it's plugged in and you actuate the manual lever all the way what does the DIC say?

If it's not showing anything, it could be a fuse got left out. It's probably a mini fuse under the hood.

[stevemedic]

Sorry for the late response... When I first plugged the trailer to my Yukon I did receive "Service Trailer Brakes" or something to that effect as I have not been able to duplicate the message since. I was able to get a reading when I squeezed the two manual applicators together but when released, nothing on my dash. Usually the break controller will automatically default on my dash screen with colored lights etc.. when it's plugged in but that doesn't happen, I have to manually scroll to that screen and still no lights indicating it's connected.
I stopped into my local RV supply and service store 2 days ago and one mechanic mentioned that GMC had a habit of not putting in the square fuse to the break controller in Yukons and Tahoe's because most people do not use them to tow large items. Luckily my GMC dealer was right next door to the RV store and I pulled into the service dept. and explained my issue and asked them about the fuse. My answer was that used to be the practice but now they all come installed. So I made an appt. to have my new vehicle serviced with them in about a week. I'll keep you all posted.

[rsdata]

are you sure something has not changed with the controller on the new 2020? Your Yukon manual probably describes something that can change the settings in your "computer" whatever that is in the Yukon. My computer is settings on my 8.1 inch radio screen... under settings then Brake Controller their are three different settings, light, medium, heavy and something else that can be set. I suspect you also have these types of settings for your controller.

You might even post the question on a GMC Yukon forum... Might save you charges at the dealership for a minor problem.

[DouglasReid]

2020, Under Warranty, take it to the dealer!

[KEN9XL]

Just following.
Curious as to what the dealership finds.

[Les Clemetson]

You may have a bad brake that's shorting out the system. I bought a brand new 5th wheel, hooked up and the brake controller wouldn't work. They tested and finally found one wheel had burned up its brake pad when it was pulled to the dealer from the plant.

[babock]

Originally Posted by Les Clemetson

You may have a bad brake that's shorting out the system. I bought a brand new 5th wheel, hooked up and the brake controller wouldn't work. They tested and finally found one wheel had burned up its brake pad when it was pulled to the dealer from the plant.

Did you mean brake magnet? Drum brakes do not have pads.

[nomad297]

Originally Posted by babock

Did you mean brake magnet? Drum brakes do not have pads.

Maybe he meant to say “shoes”?

Bruce

[Wileykid]

When you said you followed the wire, did you mean the brake wires on the trailer? Reason is that I had similar issues on my chevy truck, and finally traced it to a pinched brake wire on the trailer near the hub. It did not give the "service brake" warning, but when I had the brake scale on the panel, it would show that it was applying the brake, or not, or partial, or not.

[Andy n Sherrie]

Possibly a rodent ate a wire while in storage.

[Les Clemetson]

I did mean shoes. The tech that figured it out said it's an easy fix, you unbolt the whole plate behind the wheel that holds the solenoid and brake shoes and bolt a new one on.

[HONDAMAN174]

I would look at your brake wires where they go inside the axles to the other side of trailer. Sounds like a wire has chaffed off the insulation and is grounding out. Pull them back a little on both sides to see if you have bare wire showing.

[LUM]

got a new 3500 GMC pick it up in Nov. could not adjust the brakes for the trailer read on computer that Gm used a controler on the trailer to mach them up still not sure if i can make mine work

[muddyrode]

have someone hook their vehicle up to your trailer plug, and see if there vehicle sees the trailer,
then you would know if it is the trailer or your vehicle
the older Chevy's you did have to install the fuse in the firewall box but not with the new ones

[mulher]

I had the same issue with my 2016 GMC 2500 and had to have the module replaced luckily under warranty, now 3 years later I am getting " service trailer brake system" warnings again when not even hooked up. Obviously a problem with these units.

[shchef56]

I Have a new 2018 GMC never used trailer plug one day im driving and get service trailer warning took to GMC they said switch failed why who knows but they have had problems with them.hope that fixed it i am going to need it soon.

[LUM]

Brake is set on 10. Will not lock up to adjust the gain

[shchef56]

I have had motor homes never TT have to pickup on 17th all done remotely been putting off but have to get it and never used controller before what number should it be on TT wieghs 5400 empty so about 6000 lbs.