2026 sierra bad brake controller

flattop · June 23

Hello, my 3 month old Sierra Elevation wont recognize a trailer with electric brakes? All the lights work correctly, but no power to the brakes?

This is the factory installed brake controller. If you manually push the knob, the display shows the power % but does not light up like my 2022 silverado.

I have an appointment with the dealer, but was checking to see if anyone else has seen this issue.

Thanks,

asilverblazer · June 24

Older trucks had to have a fuse and wire connected underhood... You could check that.

I've noticed a lot of aftermarket discrepancies between wire standard colors/plug terminal location function. If you've never used the trailer on a GM truck it might be something to check.

newdude · June 24

21 hours ago, flattop said:

Hello, my 3 month old Sierra Elevation wont recognize a trailer with electric brakes? All the lights work correctly, but no power to the brakes?

This is the factory installed brake controller. If you manually push the knob, the display shows the power % but does not light up like my 2022 silverado.

I have an appointment with the dealer, but was checking to see if anyone else has seen this issue.

Thanks,

Sounds like the trailer brake power module failed. Common on these.

flattop · June 24

I had asked the tech when I scheduled the appointment about adding the 40 amp fuse like the old days, he said he did not know and they need to see the truck! He acted like this has never happened before and was not a common failure?

newdude · June 24

10 minutes ago, flattop said:

I had asked the tech when I scheduled the appointment about adding the 40 amp fuse like the old days, he said he did not know and they need to see the truck! He acted like this has never happened before and was not a common failure?

I see them do them all the time at work. Fuse won't fix a bad module.

They recalled the power modules on the HDs for them failing on 2020-2024 HDs but they use the exact same module. We've done some 2024-2026 1/2 tons already that needed a new power module.

Other possibility is corroded wiring. There's a spot the chassis harness runs to the back along the frame rail. We had a 2025 that had a bad section of wire there but I think it was for a different issue.

Edited June 24 by newdude

flattop · 2026-07-07T16:19:31Z

On 6/23/2026 at 5:51 PM, flattop said:

Hello, my 3 month old Sierra Elevation wont recognize a trailer with electric brakes? All the lights work correctly, but no power to the brakes?

This is the factory installed brake controller. If you manually push the knob, the display shows the power % but does not light up like my 2022 silverado.

I have an appointment with the dealer, but was checking to see if anyone else has seen this issue.

Thanks,

Update!

Had the dealer look at the issue. First tech says no problem?? I said there was no voltage on the brake terminal on the 7 pin connector! He said he did not know what pin I was talking about. So they bring out a seasoned tech and I explain to him. He attaches a VOM and has me push the brake, and sees no voltage!!

Tom, the seasoned guy says lets go back to my service bay and look closer. We discover thru his on line system that the controller is a "smart controller" as it needs to detect a trailer connected before the brake voltage is allowed to the 7 pin connector!!! He also showed me a GM bulletin stating some trailers with LED lights have such low resistance the controller wont recognize them!!! I was thinking WTF, but thanked him for bringing me back into the service bay and explaining this all to me. He also plugged in a trailer simulator and it showed the brake controller was indeed working.

After my dealership visit I hooked up to an older camper with standard 1157 lights and the truck did connect and the electric brakes worked great!

Not to sure what I have to do with the equipment trailer with LED lights, I cant tow it with no brakes.

Why did something so simple for many years have to get so complicated!

asilverblazer · 2026-07-07T17:41:10Z

1 hour ago, flattop said:

Why did something so simple for many years have to get so complicated!

Right?!

Could you swap out the lights to an older style?

Did they say what circuit it had to detect resistance on?

It shouldn't be the running lights because those aren't on all the time, it could be the brake/turn signal circuit(s), but it seems that there might be a scenario where I would want the trailer brakes at the same time as when those lights first illuminate to recognize the trailer in the first place.

If it's the 12v +, to charge trailer batteries, maybe adding a battery backup break away to the trailer would resolve the issue.

davester · 2026-07-07T19:51:33Z

If it is just due to low resistance, then I would add LED hyperflash resistors to the left and right brake/turn signal lights, and if that doesn't work, perhaps the parking iights as well.