You are correct about the back flow charge from the solar panel back to the truck through the 7 pin connector. I fixed this on my 2024 GMC 2500 Denali HD by just simply installing a diode in the black 12 volt line of the 7 pin connector at the terminal block on my 5th wheel. Allows the truck to continue to trickle charge the rv batteries but does not allow any voltage to travel back to the truck. Works perfectly for less than $20.
I have this same problem with a 2012 Ford f250 HD, pulling a flatbed trailer. Random "Trailer Disconnected" messages, that come and go. I only pull an RV twice a year, 150 miles each way, and have not noticed this problem. Do I try to fix it or just live with it?
I had an Prodigy RF brake controller installed when I purchased my trailer. It seemed like a great idea at the time since I could switch tow vehicles by just bringing my RF controller to whatever vehicle I wanted to use. Unfortunately,after a couple of years, I started getting intermittent brake system failures while driving where an error message would start flashing on the brake controller screen and I had no trailer brakes. I did extensive testing of all of my electrical cables and connectors wiggling every single wire and connector with an Ohm meter attached with audio feedback enabled so I could hear if the connection was interrupted when wiggled. I cleaned and lubed my connectors. I also measured the resistance of my ground connections with a million meter. II tested my lead-acid battery which I keep connected when driving to power the brakes in case of a trailer disconnect but could find nothing wrong, anywhere. I called Prodigy and they blamed the wiring in my trailer and got nowhere with them. There seems to be no way to diagnose the brake controller itself so I then purchased the top of the line hardwired Prodigy brake controller that came with on-screen diagnostics thinking I might be able to use it to isolate the problem when it happened while driving. To my surprise and delight, the problem went away after I installed the new brake controller and hasn’t come back. I suggest to anyone having this problem that they try replacing their brake controller. With the consequences of brake failure being so severe, it seems to me it’s a no brainer to replace a relatively inexpensive brake controller just to be sure.
I have a 2020 Chevy 2500 that I bought about six months ago that I use to tow an Ember travel trailer (two big lithium batteries, 800W solar). When initially plugged in, everything worked with trailer lights/brakes. Then, I would receive the disconnect message after 2-3 minutes. On the Duramax forum, I found a technical service bulletin about this very issue. I went to a GM dealer and they replaced the trailer light controller module at no charge. No issues since. I assume this is something similar and the truck owner will have to do some Internet searching for the answer. The GM dealer was not aware of the TSB in my case.
Great theory, but… my 2015 GMC 3500 will often give me the tones and message with no trailer attached at all. This is an extremely common GM issue that they don’t have a clue on how to correct. I have found that a plastic bread bag closer, slipped between the 7-way coupling (or part of a zip tie) the stop any wiggling seems to help.
Note the problem I’m discussing in this post is exclusively for the 2024 GM trucks with integrated brake controllers. But I’ll start publishing about general/older trailer brake troubleshooting soon.
I have 2024 2500 hd have solar and if I take out the 30 amp fuse on truck and plug it into trailer it works good no issue.now if I use disconnect on trailer and leave fuse in truck it works that way too when truck is plugged into truck everything works inside tailer
GM provided a replacement controller for this solar/lithium issue. I did not solve the intermittent connect/disconnect problem with my Hydrastar Electric over Hydraulic brakes system. It also did not solve the problem of not recognizing the led lights in my trailer.
I have a 2024 GMC 2500 HD and tow 10,000 lb man lift-total load with trailer 12,500lbs. The trailer has hydraulics to tilt the trailer and a lead acid battery to power this. We do not have a solar panel attached to the system. We are having a problem with our electronic controller. It intermittently posts a message "check trailer wiring" and during this time there are no trailer brakes. We have towed the same trailer with two other vehicles and do not have a problem. We have had the trailer checked and cannot find a wiring problem. GMC has refused to put me into contact with a regional service tech that has technological knowledge regarding this subject. Some of the online posts that we have read state that solar chargers can input higher voltage than the tow vehicle battery voltage causing interference with the controller. As stated above we do not have a solar charger, but the trailer battery does have a higher voltage reading than our tow vehicle, and we are experiencing the same problems. My question is what might happen if the battery on the tow vehicle becomes slightly run down, the truck starts but now the voltage in the tow vehicle is less than the battery in the trailer. Does this mean that there could be brake malfunction? This is a severe safety issue. We have been able to eliminate the warning message by pulling the trailer charging fuse in the vehicle fuse block (#84). We have also been able to eliminate the message by disconnecting the emergency brake positive lead from the trailer battery which eliminates the trailer emergency brakes. Both of these solutions indicate that GMC has a problem with their controller. GMC promotes their trucks as GMC grade Professional Grade. You would think that their Professional Grade engineers would be aware of the different trailer types and wiring configurations when they designed the electronic controller. Apparently not as they refuse to admit that they have a problem. I urge everyone to file a complaint with the NTSB before someone is killed or injured as a result of a faulty controller.
I have a 2024 GMC 2500 HD and tow 10,000 lb man lift-total load with trailer 12,500lbs. The trailer has hydraulics to tilt the trailer and a lead acid battery to power this. We do not have a solar panel attached to the system. We are having a problem with our electronic controller. It intermittently posts a message "check trailer wiring" and during this time there are no trailer brakes. We have towed the same trailer with two other vehicles and do not have a problem. We have had the trailer checked and cannot find a wiring problem. GMC has refused to put me into contact with a regional service tech that has technological knowledge regarding this subject. Some of the online posts that we have read state that solar chargers can input higher voltage than the tow vehicle battery voltage causing interference with the controller. As stated above we do not have a solar charger, but the trailer battery does have a higher voltage reading than our tow vehicle, and we are experiencing the same problems. My question is what might happen if the battery on the tow vehicle becomes slightly run down, the truck starts but now the voltage in the tow vehicle is less than the battery in the trailer. Does this mean that there could be brake malfunction? This is a severe safety issue. We have been able to eliminate the warning message by pulling the trailer charging fuse in the vehicle fuse block (#84). We have also been able to eliminate the message by disconnecting the emergency brake positive lead from the trailer battery which eliminates the trailer emergency brakes. Both of these solutions indicate that GMC has a problem with their controller. GMC promotes their trucks as GMC grade Professional Grade. You would think that their Professional Grade engineers would be aware of the different trailer types and wiring configurations when they designed the electronic controller. Apparently not as they refuse to admit that they have a problem. I urge everyone to file a complaint with the NTSB before someone is killed or injured as a result of a faulty controller.
I tow a 2019 Vanleigh Villano 320GK fifth wheel with a 2022 GMC 3500HD. I installed LFP battery with solar panels charging the LFP battery in the trailer. My LFP battery sits around 14.6V most of the time during tow. I read about the issues with new GMCs and the service bulletin which spoke to issues presented to the truck by high voltage at the trailer on the charging pin. As a precaution I pulled the fuse on the truck to disable charging the trailer battery. Then we did a 3 week trip towing and did not have any issues with trailer brakes no messages, etc.
I have been having the exact same problem with my 2009 GMC 2500HD Duramax. Apparently GM has never solved this issue for years and has no desire to correct it. Very, very dangerous situation indeed.
I not only put a shut-off switch between the solar charge controller and the panels, but I put a diode in the trailer between the batteries and the end of the cord to hook into the truck 7-way. Both are a fail. Neither worked. Still getting "Check trailer brakes, Trailer Brakes Disconnected, Trailer Brakes connected"
Mike, Turns out that every 2024 Chevy/GMC HD2500 or 3500 towing a trailer with solar in USA is having this problem. I put in a disconnect between the solar panel and the solar charge controller - it was still throwing warnings on the dash. The GMC dealer is playing dumb. I am going to try a diode from the hot 12v from the truck to the trailer.
After installing the shutoff switch between the solar panels and the solar charge controller,
I still received a message on the dash. I determined that BEFORE hooking up the trailer, the trailer batteries had already a maximum charge on them from the solar panels. Hooking it up and there was too many volts causing the brake controller shutting down. After more research, I ordered, Roadmaster 690 Single Park Light Diode on Amazon for $17. I will put this on the charging cable from the hitch connector to the battery. This way, the truck can send power to the trailer batteries and not back to the truck.
As always you are on top of this stuff. Great job, Mike
You are correct about the back flow charge from the solar panel back to the truck through the 7 pin connector. I fixed this on my 2024 GMC 2500 Denali HD by just simply installing a diode in the black 12 volt line of the 7 pin connector at the terminal block on my 5th wheel. Allows the truck to continue to trickle charge the rv batteries but does not allow any voltage to travel back to the truck. Works perfectly for less than $20.
I have this same problem with a 2012 Ford f250 HD, pulling a flatbed trailer. Random "Trailer Disconnected" messages, that come and go. I only pull an RV twice a year, 150 miles each way, and have not noticed this problem. Do I try to fix it or just live with it?
Does your trailer have electric brakes? If so, then I think it’s worth finding and fixing the problem.
I had an Prodigy RF brake controller installed when I purchased my trailer. It seemed like a great idea at the time since I could switch tow vehicles by just bringing my RF controller to whatever vehicle I wanted to use. Unfortunately,after a couple of years, I started getting intermittent brake system failures while driving where an error message would start flashing on the brake controller screen and I had no trailer brakes. I did extensive testing of all of my electrical cables and connectors wiggling every single wire and connector with an Ohm meter attached with audio feedback enabled so I could hear if the connection was interrupted when wiggled. I cleaned and lubed my connectors. I also measured the resistance of my ground connections with a million meter. II tested my lead-acid battery which I keep connected when driving to power the brakes in case of a trailer disconnect but could find nothing wrong, anywhere. I called Prodigy and they blamed the wiring in my trailer and got nowhere with them. There seems to be no way to diagnose the brake controller itself so I then purchased the top of the line hardwired Prodigy brake controller that came with on-screen diagnostics thinking I might be able to use it to isolate the problem when it happened while driving. To my surprise and delight, the problem went away after I installed the new brake controller and hasn’t come back. I suggest to anyone having this problem that they try replacing their brake controller. With the consequences of brake failure being so severe, it seems to me it’s a no brainer to replace a relatively inexpensive brake controller just to be sure.
I have a 2020 Chevy 2500 that I bought about six months ago that I use to tow an Ember travel trailer (two big lithium batteries, 800W solar). When initially plugged in, everything worked with trailer lights/brakes. Then, I would receive the disconnect message after 2-3 minutes. On the Duramax forum, I found a technical service bulletin about this very issue. I went to a GM dealer and they replaced the trailer light controller module at no charge. No issues since. I assume this is something similar and the truck owner will have to do some Internet searching for the answer. The GM dealer was not aware of the TSB in my case.
I’ve had a least a dozen emails about the 2024 GM trailer brake problem, so this must be a new thing.
Great theory, but… my 2015 GMC 3500 will often give me the tones and message with no trailer attached at all. This is an extremely common GM issue that they don’t have a clue on how to correct. I have found that a plastic bread bag closer, slipped between the 7-way coupling (or part of a zip tie) the stop any wiggling seems to help.
Note the problem I’m discussing in this post is exclusively for the 2024 GM trucks with integrated brake controllers. But I’ll start publishing about general/older trailer brake troubleshooting soon.
When you say GM, are you including Chevy’s?
Yes indeed!
Many semi drivers use a similar technique to solve light problems on their trailers. I was one of them.
I have 2024 2500 hd have solar and if I take out the 30 amp fuse on truck and plug it into trailer it works good no issue.now if I use disconnect on trailer and leave fuse in truck it works that way too when truck is plugged into truck everything works inside tailer
GM provided a replacement controller for this solar/lithium issue. I did not solve the intermittent connect/disconnect problem with my Hydrastar Electric over Hydraulic brakes system. It also did not solve the problem of not recognizing the led lights in my trailer.
I’ve been trying to get GM to provide me with a loaner test vehicle, but so far no go. Where are you located?
Tucson
New Orleans
I have a 2024 GMC 2500 HD and tow 10,000 lb man lift-total load with trailer 12,500lbs. The trailer has hydraulics to tilt the trailer and a lead acid battery to power this. We do not have a solar panel attached to the system. We are having a problem with our electronic controller. It intermittently posts a message "check trailer wiring" and during this time there are no trailer brakes. We have towed the same trailer with two other vehicles and do not have a problem. We have had the trailer checked and cannot find a wiring problem. GMC has refused to put me into contact with a regional service tech that has technological knowledge regarding this subject. Some of the online posts that we have read state that solar chargers can input higher voltage than the tow vehicle battery voltage causing interference with the controller. As stated above we do not have a solar charger, but the trailer battery does have a higher voltage reading than our tow vehicle, and we are experiencing the same problems. My question is what might happen if the battery on the tow vehicle becomes slightly run down, the truck starts but now the voltage in the tow vehicle is less than the battery in the trailer. Does this mean that there could be brake malfunction? This is a severe safety issue. We have been able to eliminate the warning message by pulling the trailer charging fuse in the vehicle fuse block (#84). We have also been able to eliminate the message by disconnecting the emergency brake positive lead from the trailer battery which eliminates the trailer emergency brakes. Both of these solutions indicate that GMC has a problem with their controller. GMC promotes their trucks as GMC grade Professional Grade. You would think that their Professional Grade engineers would be aware of the different trailer types and wiring configurations when they designed the electronic controller. Apparently not as they refuse to admit that they have a problem. I urge everyone to file a complaint with the NTSB before someone is killed or injured as a result of a faulty controller.
What are the voltage readings for your truck battery and trailer battery when the trailer is disconnected and the truck is at idle?
I have a 2024 GMC 2500 HD and tow 10,000 lb man lift-total load with trailer 12,500lbs. The trailer has hydraulics to tilt the trailer and a lead acid battery to power this. We do not have a solar panel attached to the system. We are having a problem with our electronic controller. It intermittently posts a message "check trailer wiring" and during this time there are no trailer brakes. We have towed the same trailer with two other vehicles and do not have a problem. We have had the trailer checked and cannot find a wiring problem. GMC has refused to put me into contact with a regional service tech that has technological knowledge regarding this subject. Some of the online posts that we have read state that solar chargers can input higher voltage than the tow vehicle battery voltage causing interference with the controller. As stated above we do not have a solar charger, but the trailer battery does have a higher voltage reading than our tow vehicle, and we are experiencing the same problems. My question is what might happen if the battery on the tow vehicle becomes slightly run down, the truck starts but now the voltage in the tow vehicle is less than the battery in the trailer. Does this mean that there could be brake malfunction? This is a severe safety issue. We have been able to eliminate the warning message by pulling the trailer charging fuse in the vehicle fuse block (#84). We have also been able to eliminate the message by disconnecting the emergency brake positive lead from the trailer battery which eliminates the trailer emergency brakes. Both of these solutions indicate that GMC has a problem with their controller. GMC promotes their trucks as GMC grade Professional Grade. You would think that their Professional Grade engineers would be aware of the different trailer types and wiring configurations when they designed the electronic controller. Apparently not as they refuse to admit that they have a problem. I urge everyone to file a complaint with the NTSB before someone is killed or injured as a result of a faulty controller.
Where are you located?
I tow a 2019 Vanleigh Villano 320GK fifth wheel with a 2022 GMC 3500HD. I installed LFP battery with solar panels charging the LFP battery in the trailer. My LFP battery sits around 14.6V most of the time during tow. I read about the issues with new GMCs and the service bulletin which spoke to issues presented to the truck by high voltage at the trailer on the charging pin. As a precaution I pulled the fuse on the truck to disable charging the trailer battery. Then we did a 3 week trip towing and did not have any issues with trailer brakes no messages, etc.
Where are you located?
Vashon outside Seattle
I did same thing and it worked . But now I just disconnect my trailer it has a switch
Located in Susanville, a small town in northeastern California, about 100 miles north of Reno, NV
Well, since I’m in Maryland that’s too long of a trip, but I’ll let everyone know when I confirm my solution works.
I have been having the exact same problem with my 2009 GMC 2500HD Duramax. Apparently GM has never solved this issue for years and has no desire to correct it. Very, very dangerous situation indeed.
Where are you located?
I not only put a shut-off switch between the solar charge controller and the panels, but I put a diode in the trailer between the batteries and the end of the cord to hook into the truck 7-way. Both are a fail. Neither worked. Still getting "Check trailer brakes, Trailer Brakes Disconnected, Trailer Brakes connected"
Mike, Turns out that every 2024 Chevy/GMC HD2500 or 3500 towing a trailer with solar in USA is having this problem. I put in a disconnect between the solar panel and the solar charge controller - it was still throwing warnings on the dash. The GMC dealer is playing dumb. I am going to try a diode from the hot 12v from the truck to the trailer.
After installing the shutoff switch between the solar panels and the solar charge controller,
I still received a message on the dash. I determined that BEFORE hooking up the trailer, the trailer batteries had already a maximum charge on them from the solar panels. Hooking it up and there was too many volts causing the brake controller shutting down. After more research, I ordered, Roadmaster 690 Single Park Light Diode on Amazon for $17. I will put this on the charging cable from the hitch connector to the battery. This way, the truck can send power to the trailer batteries and not back to the truck.