2025 GMC Sierra 3500

The electronic part of the truck gave a warning and shut off my trailer brake system while towing a 21K 5th wheel trailer (X2). The truck is available for inspection. Any part of the electronics package that has the ability to disable a trailer braking system while towing needs to be removed/disabled immediately. The truck has not been seen by a dealer yet. yes there was a warning I briefly saw both times, but I can't say what it said.

The truck automatically engages the parking brake ONLY when on an incline, never at any other time. I am so used to engaging the parking brake at all other times I also engage it when on an incline. The problem is the truck DISENGAGES the brake automatically after I've engaged it. This has happened multiple times when I've been towing a large boat on a launch ramp or towing my heavy 5th wheel. I can be fully exited from the truck and 10 ft away when it disengages and I watch it lurch forward. Simple answer would be for me to not engage the brake on an incline, but its a total habit all the time so I never remember to not engage it on an incline. This is a dangerous feature that needs to be removed ASAP. Thank you

While towing my fifth wheel trailer, the truck intermittently disconnects the trailer brakes while in motion. This results in a sudden loss of roughly 75% of my braking capability, creating an extremely dangerous situation. I have a professional driving background, which has helped me avoid an accident so far, but this issue could easily result in a collision, especially under emergency braking or downhill conditions Service Attempt: On June 17, 2025, I brought the vehicle to Madras Chevrolet in Oregon. The dealership acknowledged the issue but stated the truck is “within GM parameters,” so no repairs were made. They claimed the problem might be with the trailer, but I’ve confirmed the trailer works properly with other tow vehicles. This appears to be a systemic electrical or control issue with the truck. Safety Concern: No vehicle should be allowed to disable trailer brakes while moving. This is a clear design or control system fault. I am concerned that other GMC or GM truck owners may be at similar risk and urge the NHTSA to investigate this problem before it results in serious injury or death. PS. On social media most owners say this is happening to them