2021 GMC Sierra 1500 transmission problems

Filed Nov 4, 2026 · Transmission · MS

GM has a known issue with coolant control valves that can cause vehicles to go into reduced power mode creating drive-ability and safety concerns in busy traffic situations. They have issued a TSB (N252508341) for certain VIN numbers but have ignored similar issues in other VINs.

Filed Oct 30, 2026 · Engine, Steering · 34,000 miles · AK

The contact owns a 2021 GMC Sierra 1500. The contact stated that while driving 45 MPH, there was an abnormal knocking sound coming from the vehicle. The vehicle started hesitating, and there was a loss of power that became worse over time. Additionally, the “Service Engine” and “Power Train” warning lights were illuminated. The messages “Loss of Steering Assist - Be Alert” and “Service Parking Brake” were displayed. The following day, the vehicle was driven in LIMP Mode to the dealer and was diagnosed with engine failure. The contact stated that there was an ongoing the federal safety agency investigation associated with the 6.2L engines. The failure mileage was approximately 34,000.

Filed Oct 28, 2026 · Transmission · MD

I am experiencing hard gear shifting in the low gears. It is very noticeable and I have a 10-speed transmission.

Filed Oct 20, 2026 · Transmission · 106,554 miles · TN

The contact owns a 2021 GMC Sierra 1500. The contact stated that while driving at 55 MPH, the accelerator pedal was depressed; however, the vehicle failed to accelerate as intended. The contact became aware of an abnormal sound, and the check engine warning light was illuminated. The vehicle was driven to the shoulder of the road. The contact inspected the vehicle and connected a portable diagnostic tester to the vehicle. The contact retrieved a pressure fault code. The vehicle was taken to the dealer, where it was diagnosed with a torque converter shudder. Additionally, the solenoids were clogged with debris. The contact was informed that the transmission needed to be replaced. The manufacturer was contacted, and a case was filed. The failure mileage was approximately 106,554.

Filed Oct 20, 2026 · Engine, Fuel system · FL

My 2021 GMC 1500 Sierra has the 6.2L motor that has significant known issues with catastrophic engine failure involving the camshaft and lifters. The engine in my truck has suffered the same failure but for some reason my VIN is not included in the recall of nearly 600,000 GMC trucks. I called GMC Customer Service and was told bluntly the recall was VIN specific and I would have to bear the 14,000 dollar repair. This is unacceptable since GMC is under federal investigation for knowingly and negligently manufacturing a flawed motor.

Filed Oct 13, 2026 · Engine, Fuel system · FL

2021 GMC with 6.2L motor. The engine begin to produce a clattering noise in the upper part of the engine. When the clattering happens the vehicle will shudder. I took the vehicle into a certified independent service center who diagnosed a catastrophic engine failure as a result of lifter and camshaft bearing failure. They further advised that this year of vehicle (2021) and engine (6.2L) was known to have this defect and might be subject to a safety recall. I contacted GM customer service who stated that my VIN was not included in the recall even though the year and engine matched the recall. I found that to be odd especially when I noted that nearly 600K vehicles matching my failed engine was recalled. She stated that I (owner) had to bear the cost of replacing the defective engine and labor. I had to have my vehicle transported from [XXX] to [XXX] at the cost of 1400 dollars. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Oct 5, 2026 · Transmission · 38,000 miles · FL

The contact owns a 2021 GMC Sierra 1500. The contact stated that the transmission was previously replaced. The contact stated that 20,000 miles later, the vehicle started to experience erratic hard shifting while driving at various speeds, and the vehicle failed to respond upon shifting into reverse(R). The vehicle was towed to the dealer, where the battery was replaced; however, the failure recurred. The contact received notification of the federal safety agency Campaign Number: 24V797000 (Power Train). The vehicle was towed back to the dealer, where it was determined that the transmission needed to be replaced. The contact was advised that the repair was not covered under the extended warranty coverage associated with the recall because the required DTC was not retrieved. The contact advised the dealer to complete the TCM software update under the recall, which would enable the generation of warning lights and DTC. After several attempts, the dealer informed the contact that the TCM software update was unsuccessful. The contact stated that the manufacturer had exceeded a reasonable amount of time for the recall repair. The manufacturer was notified of the failure by phone and email, a case was filed, and documents were sent to the manufacturer. The failure mileage was approximately 38,000.

Filed Oct 1, 2026 · Electrical, Engine · IN

Received Re-Call for Engine Failure! Dealer replaced Engine Oil and Oil Cap @ 85,544 Miles. I read of the Re-call prior to the notice and I waited for it to come. After I received it and the Dealer made the changes, it made me afraid to leave town using my truck for fear of a breakdown on the Freeway. I use a Walker, so if I broke down and I was in the left lane and lost all power it would be very dangerous for me to get to the right side of the road! The truck started using excessive Oil after they changed the oil. I replaced four (4) quarts of oil @ 2526 miles! Speedometer reading 88070 miles.

Filed Oct 1, 2026 · Engine, Fuel system · CA

1. I am being told that the high-pressure fuel pump (HPFP) catastrophically seized and locked up internally while driving. Because the HPFP on the 3.0L Duramax (LM2) engine is directly driven by the engine's timing system, this sudden mechanical seizure instantly destroyed the engine timing gears and snapped/skipped the timing chain. The failed components are currently intact inside the vehicle and are fully available for inspection upon request at Ron's Smith GMC in Merced, CA. 2. The failure occurred on busy Labor Day (XXX) while our family of [XXX] was traveling back home at 70 mph on a major highway. The truck violently shook, instantly lost all engine power, and forced the vehicle into a dangerous limp-mode state before completely stalling in live highway traffic at night around 10:45 pm. This sudden loss of propulsion at high speed severely compromised our ability to safely navigate out of the way of fast-moving highway traffic, creating an immediate & extreme risk of a high-speed rear-end collision. At times hazard lights didn't work causing family panic & screaming as truck shook with passing traffic. 3. The problem has been officially confirmed by Ron Smith GMC in Merced, CA. Their service department diagnosed the issue, confirming that the high-pressure fuel pump had locked up and subsequently destroyed the timing belt/chain & engine gears. 4. The vehicle and its failed components have only been inspected by technicians at the Ron Smith GMC dealership service department. No police, insurance representatives, or outside third parties have inspected the vehicle yet. 5. I had been extremely happy with my truck and there were absolutely no warning lamps, dashboard messages, or driving symptoms prior to the failure. The truck was operating perfectly normally under cruise until the exact moment of the failure, at which point a "Reduced Engine Power" warning flashed on the dashboard simultaneously with the mechanical lock-up, shaking, and immediate stall. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF

Filed Sep 30, 2026 · Engine, Fuel system · CA

1. I am being told that the high-pressure fuel pump (HPFP) catastrophically seized and locked up internally while driving. Because the HPFP on the 3.0L Duramax (LM2) engine is directly driven by the engine's timing system, this sudden mechanical seizure instantly destroyed the engine timing gears and snapped/skipped the timing chain. The failed components are currently intact inside the vehicle and are fully available for inspection upon request at Ron’s Smith GMC in Merced, CA. 2. The failure occurred on busy Labor Day (XXX) while our family of [XXX] was traveling back home at 70 mph on a major highway. The truck violently shook, instantly lost all engine power, and forced the vehicle into a dangerous limp-mode state before completely stalling in live highway traffic at night around 10:45 pm. This sudden loss of propulsion at high speed severely compromised our ability to safely navigate out of the way of fast-moving highway traffic, creating an immediate & extreme risk of a high-speed rear-end collision. At times hazard lights didn’t work causing family panic & screaming as truck shook with passing traffic. 3. The problem has been officially confirmed by Ron Smith GMC in Merced, CA. Their service department diagnosed the issue, confirming that the high-pressure fuel pump had locked up and subsequently destroyed the timing belt/chain and engine gears. 4. The vehicle and its failed components have only been inspected by technicians at the Ron Smith GMC dealership service department. No police, insurance representatives, or outside third parties have inspected the vehicle yet. 5. I had been extremely happy with my truck and there were absolutely no warning lamps, dashboard messages, or driving symptoms prior to the failure. The truck was operating perfectly normally under cruise until the exact moment of the failure, at which point a "Reduced Engine Power" warning flashed on the dashboard simultaneously with the mechanical lock-up, shaking, and immediate stall. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF