2025 2500 Brake Controller Disconnecting

[Jacejr66]

Yeah, my dealer pretty much ******. They could do nothing after they hook their tester up and shows fine. I ordered a brake control module from a 21 part number that’s what I had on my last one was and I never had any issues.

[mjonesjr84]

3 minutes ago, Jacejr66 said:

Yeah, my dealer pretty much ******. They could do nothing after they hook their tester up and shows fine. I ordered a brake control module from a 21 part number that’s what I had on my last one was and I never had any issues.

Did the '21 module work on your 2025? I have a module for the '19-23 models that is NIB.

[UWSkier]

There's a recall for the 2024s where they replace the TBCM with an updated unit.  The fix was originally to put in a 2023 module.  But last time I had my truck in, they said there was ANOTHER recall on the 2024 TBCM and swapped my module again.  I've towed my RV 6000 miles since then with no brake issues, though I did also install a diode in the line to kill the problem.

 

In the 2024s, the issue was that the TBCM just decided to disconnect the trailer brakes any time the voltage on the trailer exceeded that of the truck.  If you have LiFePO4 batteries and a charge controller for them, you're likely occasionally pushing voltage back to the truck rather than the other direction from the alternator.

 

A diode from the trailer to the truck fixed the issue for the 2024s.  Surprised to see this happening on a 2025.

[mjonesjr84]

2 hours ago, UWSkier said:

There's a recall for the 2024s where they replace the TBCM with an updated unit.  The fix was originally to put in a 2023 module.  But last time I had my truck in, they said there was ANOTHER recall on the 2024 TBCM and swapped my module again.  I've towed my RV 6000 miles since then with no brake issues, though I did also install a diode in the line to kill the problem.

 

In the 2024s, the issue was that the TBCM just decided to disconnect the trailer brakes any time the voltage on the trailer exceeded that of the truck.  If you have LiFePO4 batteries and a charge controller for them, you're likely occasionally pushing voltage back to the truck rather than the other direction from the alternator.

 

A diode from the trailer to the truck fixed the issue for the 2024s.  Surprised to see this happening on a 2025.

I have a LiFePO4 battery on my crawler hauler. I talked to HydraStar and bought their recommended modules. We shall see how it works next week.

 

I also have a '23 TBCM that is new in the box to go in as well. Hopefully the HydraStar modules work and I can send. It back.

[mjonesjr84]

On 9/10/2025 at 5:35 PM, GMCustomerService said:

We know this must be an upsetting problem, Maurice. Our team would like to act as an extra layer of assistance on your behalf during and after your appointment on the 15th. So that we can connect with you, please email us at [email protected] with "GM TRUCKS - mjonesjr84" in the subject line. By sending us a message, you consent to the information you provide being monitored and recorded by GM or those acting on GM’s behalf, subject to the GM Privacy Statement: https://www.gm.com/privacy-statement.

I emailed you a message this morning regarding my truck disconnecting the trailer brakes. This is a major safety issue that I need help getting fixed.

[Jacejr66]

On 9/25/2025 at 10:51 AM, mjonesjr84 said:

Did the '21 module work on your 2025? I have a module for the '19-23 models that is NIB.

I have not got it installed yet but I will post as soon as I get it done and let you know if it corrects the problem