2025 GMC Sierra 3500 problems

Filed Nov 2, 2026 · Brakes · OR

While trying to slow from freeway speed at an off-ramp, the braking system while in tow mode turned off while towing a 21K 5th wheel. I almost could not stop in time. The voltage of the trailer system has been checked and is good. This is the 4th time the braking system has turned off the trailer brakes while in tow mode. appointment with GMC has been made; this will be the second time the truck has been seen for this issue. From a safety point of view, NO electronic system should be allowed to reduce the braking capacity or potential to brake on any vehicle system for any reason. It put me and others who could have been hit by me in danger.

Filed Oct 5, 2026 · Body, Wheels · WA

At approximately 9,000 miles and 9 months of ownership, both front wheelhouse liners on my 2025 GMC Sierra 3500HD Denali Ultimate permanently deformed and sagged into the front tire clearance area. The truck is completely stock, including the factory wheels, tires, suspension, and ride height. No modifications have been made that would affect tire-to-wheelhouse clearance. The condition occurred during approximately four hours of highway towing at approximately 65 MPH while pulling a travel trailer weighing approximately 12,000 pounds. Ambient temperature was approximately 105 - 114°F and side winds were approximately 20 MPH. Both front wheelhouse liners became visibly deformed and sagged downward toward the tires. Both liners now contact the factory front tires during normal steering, particularly during tighter low-speed turns such as parking-lot maneuvers. On the driver's side, repeated tire contact has worn completely through the wheelhouse liner, leaving a hole and exposing components behind the liner. I temporarily tied the driver's-side liner back to reduce further tire contact, but because the liner has permanently lost its original molded shape, tire interference can still occur during tight turns. The passenger-side liner has not been tied back or otherwise modified and shows similar deformation and tire interference. There was no collision, road-debris impact, tire failure, or other known event that caused the damage. The vehicle was being operated normally and towing a load appropriate for a GMC Sierra 3500HD. I am reporting this as a potential safety defect because the factory wheelhouse liners have deformed sufficiently to contact rotating front tires on an unmodified vehicle. Continued contact could potentially damage a tire or surrounding components and may affect safe vehicle operation. Photographs document the deformation, tire-contact area, hole worn through the driver's-side liner, and similar deformation of the passenger-side liner.

Filed Apr 19, 2026 · Brakes · OR

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.

Filed Apr 15, 2026 · Brakes · AK

The contact owns a 2025 GMC Sierra 3500 used for hauling a 2026 Aluminum Trailer equipped with a DeeMaxx: DBI-7K-MAXX-SS-KIT brake kit. The contact stated that while driving at an undisclosed speed, the brake caliper bracket detached due to insufficient generic quality bolts included in the brake kit. The contact pulled over and had the trailer towed to an RV park. The vehicle was not diagnosed or repaired by an independent mechanic or dealer. The manufacturer was made aware of the failure but informed the contact that the failure was caused by improper installation. The failure mileage was unknown. The VIN was not available.

Filed Apr 1, 2026 · Engine, Transmission · 40,000 miles · FL

The contact owns a 2025 GMC Sierra 3500. The contact stated that the transmission was shifting hard and was jerking while shifting gear. Additionally, the vehicle failed to accelerate above 50 MPH. The messages “Reduced Acceleration” and “DEF Low” were displayed. While refueling the vehicle, the fuel gauge failed to correctly display the level of fuel inside the fuel tank until the vehicle had been driven for approximately 20 minutes. The vehicle was taken to the dealer to be diagnosed, and the contact was informed that the transmission needed to be updated. The system was recalibrated; however, the failure persisted. The vehicle was taken to another dealer, George Kell Motors (3808 Van Dyke Rd, Newport, AR 72112); and the system was recalibrated. However, the failures persisted. While driving approximately 60 MPH, the transmission was shifting hard, and the vehicle took over 2 hours to drive 19-miles. The engine temperature gauge fluctuated between 185 and 188 degrees. The vehicle was pulled over to the side of the road to cool down before continuing to drive, while not exceeding 40 MPH. The vehicle was taken to a third dealer, Fremont Chevrolet GMC Riverton (1401 N Federal Blvd, Riverton, WY 82501); who determined that the bell body needed to be replaced. The vehicle was scheduled to be repaired, but parts were on back order. The contact became aware that there was a recall related to failure; the federal safety agency Campaign Number: 26V129000 (Fuel System, Gasoline); however, the VIN was not included. The manufacturer was not made aware of the failure. The failure mileage was approximately 40,000.

Filed Mar 23, 2026 · Tires · WA

I am reporting a potential safety defect involving Goodyear Wrangler TrailRunner AT tires size LT275/65R20. I purchased a new 2025 GMC Sierra 3500HD in August 2025. By the time the vehicle reached approximately 1,800 miles, noticeable sidewall bulges appeared on both rear tires. As a 36-year automotive professional, I recognized the serious safety risk posed by this condition and replaced all four tires at my own expense with a different brand. Since then, I have seen multiple reports of similar sidewall failures on brand-new trucks, which suggests this may be a systemic issue. Based on my experience and these reports, I believe this defect may be known to both Goodyear and GM but has not been adequately addressed. I urge the federal safety agency to investigate this matter to determine whether these tires pose a significant safety risk to the public. Vehicle Information: Make & Model: 2025 GMC Sierra 3500HD Tire Model: Goodyear Wrangler TrailRunner AT tire size LT275/65R20. Mileage at Issue: ~1,800 miles Purchase Date: August 2025 Summary of Issue: Sidewall bulging on new tires, potential for blowout or loss of vehicle control.

Filed Mar 8, 2026 · Electrical, Lights · OR

Randomly when the truck is turned on, the turn signals will stop working, no noise, nothing. When this happens, the infotainment system also stops working. It is unsafe to be driving and not knowing if your signals are working or not. This has been happening since the truck was purchased from the dealer.

Filed Jan 30, 2026 · Brakes · WA

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

Filed Dec 22, 2025 · Engine · WI

Oil cooler for truck is defective and thus allowed all oil to be mixed with the coolant. GM is stating they will flush engine and replace with exact same part. Very common issue and sad to have a $100k truck and it is junk.

Filed Dec 18, 2025 · Driver assistance · CA

Picked up vehicle from Dealership new, with 12miles on the odometer. During the trip home (over 150+ miles each way) and at 54 miles a "Forward Collision System Unavailable" warning message appeared on the dash. Stopped for coffee and restarted the vehicle and the error cleared. It re-appeared at 235 miles, and again at 427 miles along with an OBD error P0700 @cycle#763, Occurrence Cycle #2608. Returned the Vehicle to the dealership service department for repairs. The vehicle was returned and we took the truck on our first trip to Yosemite and while driving it the cruise control released the throttle times driving on a 4 lane Hwy 152. Then on the backside of Pancho Pass we entered the town of Los Banos. While driving in a 45 MPH section of Hwy 152, with no other cars in front or behind us, the truck performed an emergency stop. It applied the brakes at maximum force causing the front to dive hard and the rear tires to lose traction with the antilock cycling the brakes on and off, causing them to slip bringing the truck to a stop. At no time did the dash or the HUD display flash the collision warning or any error messages, I applied throttle and moved the Truck off the Hwy to the side of the road. Checked all pages on the dash for any indication of problems, and we drove to a parking lot inspecting the truck top to bottom to see if there were any obstructions, damage to the bumper sensors, or windshield. Returned the Truck to the dealership a second time for repairs. Received the vehicle back and during the drive home we Stopped for Dinner in San Jose and the "Forward Collision System Unavailable" returned again. Returned the vehicle for service a third time and notified Manufacture of the issues.This is a Major safety defect that GM cannot seem to repair. Current mileage of vehicle 3098.