2025 2500 Brake Controller Disconnecting

[mjonesjr84]

I have a 2025 2500 L5P and every time I tow my RV (with both a lead acid and LiFePO4 battery & NO solar), the trailer brakes disconnect when I am using them. It is concerning since my RV weighs in at 17,800# and I am trying to stop. I leave plenty of room, but I got in a jam on Wednesday where it was emergency braking and they disconnected. Thankfully I had an escape route on the shoulder. They sometimes will reconnect and sometimes I have to restart the truck for them to connect. The lights and everything else still works. I have tried disconnecting the battery and it still does it.

 

Anyone have any ideas? I have an appointment with the dealership on 9/15. Since the 2025 doesn't have the recall, has anyone successfully got a dealer to replace the module and it fix the issue?

[MG386]

Same issue on my 24 3500 pulling my boat.  I've had the recall done btw. I'm using EOH brakes and the problem has to due with the emergency breakaway battery on the trailer feeding power back to the truck.  If your using a hydrastar unit, they sell a diode that you can wire in to fix the issue.  I have the diode but haven't wired it in yet.

[mjonesjr84]

1 hour ago, MG386 said:

Same issue on my 24 3500 pulling my boat.  I've had the recall done btw. I'm using EOH brakes and the problem has to due with the emergency breakaway battery on the trailer feeding power back to the truck.  If your using a hydrastar unit, they sell a diode that you can wire in to fix the issue.  I have the diode but haven't wired it in yet.

I've seen that. I'm not running EOH, just the standard electric brakes. I've thought about installing a diode in the brake wire to see if that works.

[MG386]

you should have an emergency breakaway battery with electric brakes also, that's where the issue is i think

[mjonesjr84]

6 minutes ago, MG386 said:

you should have an emergency breakaway battery with electric brakes also, that's where the issue is i think

I have thought about removing it and using the onboard LiFePO4 battery. 

 

Does the diode go in the power wire feeding the emergency battery or the blue brake wire?

[MG386]

The diode installs on the blue brake wire.  The LiFePO4 battery might be an interesting idea.  I would imagine it uses a battery management system that could possibly prevent the electricity backflow?

[mjonesjr84]

3 minutes ago, MG386 said:

The diode installs on the blue brake wire.  The LiFePO4 battery might be an interesting idea.  I would imagine it uses a battery management system that could possibly prevent the electricity backflow?

Just to confirm, the blue brake wire from the truck to the junction box with flow towards the trailer?

 

I'm going to try that before ripping the emergency battery out and rewiring the emergency brakes.

[MG386]

Yes the blue brake wire between the 7 pin and the junction box. the hydrastar diode is labeled to show which way it installs.  I think it prevents power going to the truck.  power should always come from the truck, to the trailer on the blue wire.

[mjonesjr84]

1 hour ago, MG386 said:

Yes the blue brake wire between the 7 pin and the junction box. the hydrastar diode is labeled to show which way it installs.  I think it prevents power going to the truck.  power should always come from the truck, to the trailer on the blue wire.

Perfect. The Hydrostar module is just a diode so I'm going to install one that I have to see if that works.

[davester]

What exactly is sending power back through the brake wire to the truck?  It's ONLY supposed to be connected to the brakes.  The emergency trailer battery should not be able to send power to that blue wire until the breakaway switch gets pulled out.

[GMCustomerService]

On 9/7/2025 at 3:55 PM, mjonesjr84 said:

I have a 2025 2500 L5P and every time I tow my RV (with both a lead acid and LiFePO4 battery & NO solar), the trailer brakes disconnect when I am using them. It is concerning since my RV weighs in at 17,800# and I am trying to stop. I leave plenty of room, but I got in a jam on Wednesday where it was emergency braking and they disconnected. Thankfully I had an escape route on the shoulder. They sometimes will reconnect and sometimes I have to restart the truck for them to connect. The lights and everything else still works. I have tried disconnecting the battery and it still does it.

 

Anyone have any ideas? I have an appointment with the dealership on 9/15. Since the 2025 doesn't have the recall, has anyone successfully got a dealer to replace the module and it fix the issue?

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.

[mjonesjr84]

I installed the Hydrostar module on the brake wire (blue) and prepped the 12v+ wire module in case it needs it. Hydrostar said I may or may not need the module on the 12v+ between the truck and trailer.

 

I also bought a GM 23306694 brake control module from the '19-'23 trucks that don't seem to have the issue. I found it on eBay for $45 shipped NOS. I've read this was a direct swap and solved the issues. I'm not going to swap this in until the dealer looks at the truck Monday or the modules don't fix the issue.

 

I am still going to take the truck in on Monday to have GM start looking at it.

[Jacejr66]

I’m having same issue the dealer told me they have done what GM will allow them to do which isn’t much test to make sure it operates and that’s all the will pay for. What did your dealership figure out?

[mjonesjr84]

5 minutes ago, Jacejr66 said:

I’m having same issue the dealer told me they have done what GM will allow them to do which isn’t much test to make sure it operates and that’s all the will pay for. What did your dealership figure out?

They told me their tester showed everything operating normally. They said they would need the truck with the trailer to do any further testing and started to play it off on the trailer.

[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 sent you an email. My dealer told me everything is working fine per their tester on my truck. I know it is not.