2021 GMC Sierra 2500 problems

SERVICE 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 transmission's parking pawl to remain stationary. This creates a severe rolling vehicle hazard, especially on inclines or when hauling/towing heavy loads. Second, when these shoes disintegrate, the loose friction debris trapped inside the enclosed drum can shift, wedge, and cause a sudden mechanical wheel lockup or severe brake dragging at highway speeds, threatening vehicle control. The problem was officially confirmed and diagnosed by an authorized General Motors dealership service center. The technician scanned the vehicle, retrieved DTC code C060B, and confirmed upon inspection that the internal parking brake shoes had completely disintegrated. There were absolutely no physical symptoms, abnormal noises, dragging sensations, or brake pedal changes prior to the failure, as the parking brake shoes sit isolated inside the rotor hub. The issue appeared suddenly on May 23, 2026, when the vehicle immediately displayed a parking brake malfunction warning lamp on the instrument cluster dashboard and completely refused to engage the electronic parking brake.

NHTSA complaint #11755097 — an unverified report by a vehicle owner.

FUEL/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.

NHTSA complaint #11753689 — an unverified report by a vehicle owner.

POWER TRAIN

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 "Service DEF System" warning with multiple diagnostic trouble codes. Repairs required replacement of the DEF tank, DEF heater assembly, and NOx sensor. These repeated failures involve major drivetrain and emissions components on a heavy-duty truck. DEF system failures can place the vehicle into reduced-power (derate) mode, limiting vehicle performance and creating potential safety concerns while driving or towing. I am submitting this complaint so these failures can be documented as part of NHTSA's evaluation of similar vehicles.

NHTSA complaint #11746749 — an unverified report by a vehicle owner.

ENGINE

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 "Service DEF System" warning with multiple diagnostic trouble codes. Repairs required replacement of the DEF tank, DEF heater assembly, and NOx sensor. These repeated failures involve major drivetrain and emissions components on a heavy-duty truck. DEF system failures can place the vehicle into reduced-power (derate) mode, limiting vehicle performance and creating potential safety concerns while driving or towing. I am submitting this complaint so these failures can be documented as part of NHTSA's evaluation of similar vehicles.

NHTSA complaint #11746749 — an unverified report by a vehicle owner.

FUEL/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 "Service DEF System" warning with multiple diagnostic trouble codes. Repairs required replacement of the DEF tank, DEF heater assembly, and NOx sensor. These repeated failures involve major drivetrain and emissions components on a heavy-duty truck. DEF system failures can place the vehicle into reduced-power (derate) mode, limiting vehicle performance and creating potential safety concerns while driving or towing. I am submitting this complaint so these failures can be documented as part of NHTSA's evaluation of similar vehicles.

NHTSA complaint #11746749 — an unverified report by a vehicle owner.

POWER 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.

NHTSA complaint #11741364 — an unverified report by a vehicle owner.

STRUCTURE:BODY:STEP/LADDER

The contact owns a 2021 GMC Sierra 2500. The contact stated that on several occasions, the automatic power side-out step failed to extend as designed. The vehicle was not diagnosed or repaired. The manufacturer was notified of the failure. The failure mileage was 93,726.

NHTSA complaint #11733416 — an unverified report by a vehicle owner.

UNKNOWN OR OTHER

XXX Power Assist Step Reversing I have a 2021 GMC Sierra 2500HD that the local dealership (Ozark MO 65714) is stating has expired and not covered by the warranty. I researched online and as I understand this recall falls under SAFTEY recalls and is to be fixed and doesn't expire? It requires no parts but the reprogramming of the K4 Assist Step Control Module. What is my next step or recourse?

NHTSA complaint #11733017 — an unverified report by a vehicle owner.

ENGINE

The contact owns a 2021 GMC Sierra 2500. The contact stated that while driving at 55 MPH, the vehicle stalled unexpectedly. There were no warning lights illuminated. The vehicle was taken to the local dealer, where it was diagnosed, and determined that the engine needed to be replaced. The engine was replaced; however, the failure recurred. While at a stop and attempting to drive around a curve, the vehicle stalled. No warning lights were illuminated. The vehicle was taken to the local dealer, where it was diagnosed with engine failure. The vehicle was not repaired. The failure mileage was approximately 77,000. The VIN was not available.

NHTSA complaint #11728457 — an unverified report by a vehicle owner.

POWER TRAIN

While driving on the highway at normal speed, my vehicle was operating completely normally with no warning lights, messages, or prior issues. Without any warning, the vehicle suddenly lost the ability to accelerate and felt as if it had been shifted into neutral. I immediately had to pull over to the side of the highway, as this created a dangerous situation with surrounding traffic. The vehicle had to be towed to a mechanic. Upon inspection, I was informed that a coolant line connected to the transmission had completely blew off, causing a rapid loss of transmission fluid and resulting in total transmission failure. I was told this was not due to a rusted or deteriorated clamp, but rather a sudden component failure. This vehicle has been meticulously maintained and I have owned it for less than one year. There were no prior symptoms, leaks, or warning signs leading up to this incident. This appears to be a sudden and unexpected mechanical failure, not caused by neglect or misuse. The loss of power while driving at highway speed posed a serious safety risk to myself and others on the road.

NHTSA complaint #11726714 — an unverified report by a vehicle owner.

ENGINE

80,000 Miles, complete engine break down. 12,000 to repair

NHTSA complaint #11715295 — an unverified report by a vehicle owner.

EXTERIOR LIGHTING

My right headlamp/ turn signal assembly began flashing at random intervals. The high beam would come on and off randomly. The entire assembly would randomly flash along with the turn signal. The headlamp would go on and off randomly. This included switching between setting. High beam, low beam, daytime running light, and completely off with no warning. This causes blinding conditions for oncoming drivers, loss of visibility for driver, and loss of visibility during inclement weather due to high beam coming on and off, then entire unit turning off. As of right now, the vehicle is undrivable due to incorrect lighting, and flashing lights.

NHTSA complaint #11709159 — an unverified report by a vehicle owner.

POWER TRAIN

Pulling into a driveway and the truck made a loud clunk and the check engine light, traction control light, and a reduced engine power light came on and the truck came to an abrupt stop. When the gear shift was put into reverse or any forward gear the truck would rev up without touching the gas pedal. The left rear wheel locked up. After paying over $700 in tow bills to get the truck towed to our house and then to the dealer we were told that the transmission had a catastrophic internal failure. This truck only has 82,000 miles on it and is a 2021!

NHTSA complaint #11703711 — an unverified report by a vehicle owner.

SERVICE BRAKES

2021 GMC Sierra 2500HD 6.6L gas 6 speed automatic transmission W/4wd After a brake service job the vehicle will randomly kick on the traction control/ABS and the right front brake will lock up. The steering wheel jerk is violent enough to remove the wheel from the drivers hands. No Traction control or ABS lights flash on the dash when this occurs and it has caused the vehicle to veer into oncoming traffic and also off the road. The dealer was unable to recreate the issue nor are there any stored codes/issues found when having the truck diagnosed. ABS and speed sensor wires have been reviewed and none were damaged during the brake job. All wheel speed sensors are functional and reading when the issue happens. This issue happens during dry or wet conditions and is random without warning.

NHTSA complaint #11692084 — an unverified report by a vehicle owner.

LATCHES/LOCKS/LINKAGES

The contact owns a 2021 GMC Sierra 2500. The contact received Manufacturer's Recall Number: N232426400, for water intrusion into the electronic gate-release switch. The vehicle was repaired. The contact stated that six months after the vehicle was repaired, the tailgate failed to operate as intended. While at the residence, the taillights and headlights were flashing. The contact also became aware that the tailgate had unlatched independently while the vehicle was parked. The message "Integrated Tailgate Open or Integrated Tailgate not Latched" was displayed. The contact stated that there was an abnormal clicking sound coming from the actuator when the tailgate opened independently. The vehicle was taken to the dealer, where it was diagnosed that there was water in the switch. The dealer informed the contact that the repairs were already made and, due to the water intrusion into the switch, the dealer refused to redo the repair under the previous recall. The vehicle was repaired. The manufacturer was notified of the failure, and denied assistance since the recall repair was already performed. The failure mileage was approximately 53,000.

NHTSA complaint #11683220 — an unverified report by a vehicle owner.

SERVICE BRAKES

Parking brake locking up. There is recall on the brake module for my year make and model but my vehicle isn't on the list and I feel it should be. I'm having the same issues as they are. I can't drive it until it is fixed. Very dangerous.

NHTSA complaint #11662387 — an unverified report by a vehicle owner.

LATCHES/LOCKS/LINKAGES

The contact owns a 2021 GMC Sierra 2500. The contact stated that the VIN was included in NHTSA Campaign Number: 24V060000 (Latches/Locks/Linkages) and the main exterior touchpad switch assembly was replaced. The contact stated that after the recall repair the second exterior touchpad switch assembly suddenly short circuited and caused the trunk to open unintendedly. The vehicle was returned to the dealer who stated that that only one exterior touchpad switch assembly was replaced, despite the remedy stating that the exterior touchpad switch assemblies would be replaced. The vehicle was not repaired. The manufacturer was informed of the failure and opened a case. The manufacturer referred the contact to the NHTSA Hotline to report the failure. The failure mileage was 55,700.

NHTSA complaint #11656282 — an unverified report by a vehicle owner.

POWER TRAIN

Radiator hose connection broke and loose fluid and transmission got broken

NHTSA complaint #11651470 — an unverified report by a vehicle owner.

POWER TRAIN

While driving down the highway pulling a trailer the truck started to slow down rapidly. We were able to pull to the side of the road before the truck came to a complete stop on its own. From that point forward, we could not get the truck to move forward even in 4WD. Ended up towing the truck back and a repair shop determined the transmission needed replaced. About 4 months later, we received notice of a recall describing a similar scenario. I submitted the invoice and documentation to GM, but my claim was denied because the codes and symptoms did not match the criteria for the recall.

NHTSA complaint #11649449 — an unverified report by a vehicle owner.

POWER TRAIN

Hard shifting. Back wheels locking up

NHTSA complaint #11648242 — an unverified report by a vehicle owner.

EXTERIOR LIGHTING

Known issue and has been attributed to a manufacturing defct, but no recall- Leaking headlight caused damage to headlight- now turn signal and headlight do not work. Entire assembly needs to be replaced, GM / Extended Warranty Company will not cover, this safety part. Head light and turn signal were working on the way to the dealer, 1 month later when we picked it up - Right turn signal malfuction reading appeared on dash, headlight blinking and will not work. Picked up on Friday 1/30/25, and made an appointment for the following Wednesday to take it back in. Was told by dealer today that the replacement will not be covered and will cost $2100.00 to replace. This is a safety part and the truck can not be driven legally or safely without both headlights working.

NHTSA complaint #11643184 — an unverified report by a vehicle owner.

LANE DEPARTURE: WARNING

Known issue and has been attributed to a manufacturing defct, but no recall- Leaking headlight caused damage to headlight- now turn signal and headlight do not work. Entire assembly needs to be replaced, GM / Extended Warranty Company will not cover, this safety part. Head light and turn signal were working on the way to the dealer, 1 month later when we picked it up - Right turn signal malfuction reading appeared on dash, headlight blinking and will not work. Picked up on Friday 1/30/25, and made an appointment for the following Wednesday to take it back in. Was told by dealer today that the replacement will not be covered and will cost $2100.00 to replace. This is a safety part and the truck can not be driven legally or safely without both headlights working.

NHTSA complaint #11643184 — an unverified report by a vehicle owner.

EXTERIOR LIGHTING

Headlight vent failed. Hid control board filled up with moisture. Headlight is flashing like emergency vehicle if it turns on at all.

NHTSA complaint #11642324 — an unverified report by a vehicle owner.