2021 GMC Sierra 2500 owner complaints
52 complaints filed with NHTSA, including 4 crashes, 1 fire, 1 injury and 0 deaths.
Problems by component
Forward Collision Avoidance3 Recent complaints
October 2, 2026Power Train
The contact owns a 2021 GMC Sierra 2500. The contact stated that while driving at an undisclosed speed, the transmission unexpectedly shifted out of first gear and the vehicle failed to accelerate as needed. The failure had occurred twice. The vehicle was towed to the dealer, who determined that the valve body needed to be replaced. The failure mileage was approximately 38,000.
August 5, 2026Service Brakes
The left rear internal "top-hat" parking brake shoes suffered a total manufacturing bonding failure, causing the friction lining to completely delaminate and detach from the metal backing plates inside the rotor hub. This triggered Diagnostic Trouble Code (DTC) C060B (Left Park Brake Actuator Circuit). The failed components were replaced by the servicing facility and are unavailable, but the official dealer diagnostic scan sheet and itemized repair invoice are preserved and available for inspection upon request. Safety was compromised in two ways. First, the mechanical failure completely disabled the electronic parking brake system, forcing a heavy-duty truck to rely exclusively on the trans
July 30, 2026Fuel/Propulsion System
After finishing a long drive south, I shut the engine off and a yellow engine code popped on. I connected my computer to it and revealed a P129F code (fuel pump control module). I have noticed that other GMC models have been included in a recall concerning this problem. The 2021 GMC 2500 Denali should be also since it is the same problem. This needs to be covered by the manufacturer since it is a constant problem.
June 26, 2026Power TrainEngineFuel/Propulsion System
I am reporting repeated failures involving both the transmission and diesel emissions (DEF) system on my 2021 GMC Sierra 2500HD Denali equipped with the 6.6L Duramax diesel engine and Allison 10-speed automatic transmission. While under warranty, the truck required replacement of the aftertreatment fuel injector and later the Reductant Control Module due to DEF/emissions system failures. General Motors also completed recall-related transmission software updates on the vehicle. At approximately 154,833 miles, the transmission began shifting improperly, set transmission fault codes, and required complete replacement at my expense. Less than 5,000 miles later, the vehicle again experienced a "S
June 1, 2026Power Train
We keep getting an error message that shows we need to service DEF SYSTEM, it also started to limit my MPH and is now locked at 55 MPH. initial check of the DEF SYSTEM shows a malfunctioning module. it has been happening over the last year to 18 months. they would reset it or it would sometimes go away on its own after having to drive it in order for the error to clear.