Troubleshooting Lack Of Brake Controller Output With A 2025 Chevy Silverado 3500

Question:

I just purchased a 2025 Silverado 3500HD. Upon plugging in 2013 Keystone Cougar 5th Wheel, all lights work, and trailer light system test initiates as it should however, the brakes do not activate as they should. I took the vehicle to dealer for diagnostic and the tech said everything is working as it should. I have read that earlier vehicle models have issues with the trailer brake controller and GM recommends replacing. Everything worked just fine with my 2015 Silverado 3500HD…I’m stumped Do you have any recommendation?

asked by: C. B

Expert Reply:

Have you tested the brake controller output on the 2025 Silverado's 7-way and confirmed that it's sending power back to the trailer when the manual override is being activated? When you say the brakes aren't activating as they should do you mean they some times activate or are weak or that they're just not activating at all? Does your Silverado have trailer detection and if so is it detecting that the trailer is attached?

I would start by testing your 7-way with a multimeter # PT89ZR to see if there's any voltage coming through. Let me know what you find and we can keep troubleshooting. Do you have access to any other trailers with brakes that you can test the truck with to see rule out the trailer being the issue?

expert reply by: Kevin C

7-Way Wiring Diagram
(click to enlarge)

C. B.

10/24/2024

Yes, I even connected a separate 2020 camper to the truck and the brakes did not appear to activate. All lights work, but I do not hear the brakes clicking on and when squeezing the manual controller, it does not hold the camper. GM tells me the dealer needs to figure it out and the dealer told me to call GM???????

Kevin C.

10/24/2024

@CB Ok, so we've isolated this to the truck. Test the brake controller output pin on the 7-way while someone else is holding squeezing the manual override to see if power is coming through. You most likely have a defective OEM brake controller or a blown fuse so I would check your trailer interface module fuse (fuse 82) and trailer brake (fuse 84).

C. B.

10/24/2024

@KevinC So the fuses are both good, but I’m not sure how to test the outputs at the plug. I’ll have to find a smart guy for that and let you know… Thanks

Kevin C.

10/24/2024

@CB You'll place the positive lead from a multimeter # PT89ZR to the brake controller output pin in the 7-way and the negative lead from the multimeter to the ground pin in the 7-way and then have a second person squeeze the manual override. If you start seeing voltage we know the brake controller is working and there's an issue with something else. I have a diagram attached above of the 7-way pins you can look at if you don't know which pins to test.