2021 GMC Sierra 1500: sudden loss of power

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 · CO

2021 GMC 3.0 Diesel have coolant control valve issues. GM has a special coverage for them under Special Coverage N252508341. That coverage covers my year make and model. I have an open case with GM under GMC Customer Assistance opened case 116070735. GM is refusing to cover it due to this cited email. "After reviewing the vehicle information, we determined that Special Coverage N252508341 does not apply because it is not associated with the vehicle identification number (VIN) on your vehicle." I had the dealership and GMC customer service confirm this. GMC told me to request goodwill assistance at the dealership which the service provider had never heard of before. I can provide all documentation needed. I had recurring P1098, followed by a reduced engine power warning and unusually loud radiator fans. I figured it may be the coolant control valve and found Special Coverage N252508341. I created an open case with GM and took it to the dealership. The dealership was ambiguous about the issue and quoted me over 2,000 dollars just for further diagnostics citing "Coolant" and "Valve" in the documentation. They also said once they find the issue it would be "more." I took it to a 3rd party mechanic for an actual understanding of the issue. The mechanic found that the issue was the coolant control valve, which I have in documentation, and recommend a clear understanding of the repair and quote for the repair.

Filed Oct 21, 2026 · Engine · AR

Engine locked up while driving down the road at highway speeds. Lost all power and had to pull to shoulder of road. Was towed to dealership and confirmed engine locked up and covered under special recall. Was looked at a few months back and passed the recall test on engine. No lights or signs of engine failure before failure.

Filed Oct 15, 2026 · Engine · 110,900 miles · KY

The contact owns a 2021 GMC Sierra. The contact stated that while driving at 60 MPH, a reduced power mode warning message unexpectedly illuminated, and the vehicle unexpectedly entered limp mode. The contact stated that the temperature gauge indicated a high temperature and the vehicle was overheating during the failure. The vehicle was taken to the dealer, where it was diagnosed that the control valve had failed and needed to be replaced. The vehicle was not repaired. The dealer informed the contact that this was a known failure and escalated the issue to the manufacturer for further assistance. The contact stated that the failure was associated with Technical Service Bulletin (TSB) N252508340 and believed the repair should have been covered under warranty. The manufacturer was made aware of the failure via telephone and website. The contact was also referred to the federal safety agency for further assistance. The approximate failure mileage was 110,900.

Filed Oct 12, 2026 · Engine · OH

While towing a trailer on 6/26/26, the 6.2L L87 engine suffered a sudden drop in oil pressure, began knocking, and completely lost motive power on the roadway. Because the engine seized instantly, the vehicle experienced a sudden loss of power steering and power braking while managing the extreme weight of a trailer. This combination created a severe and immediate safety hazard, forcing me to maneuver a heavy, unpowered truck and trailer combination through active traffic to the shoulder without full steering or brake control, putting my life, my passengers' lives, and the safety of surrounding motorists at extreme risk. My dad read the codes before we took it to my mechanics and the only code I can remember is P0016. I took it and dropped it off at my local mechanics on 6/28/26. This is what my mechanic said: No Start-Truck came in not running. Had timing codes. I believe the crank bearing failed causing the engine to lose oil pressure. With the sudden loss of oil pressure, the timing chain tensioner slacked and caused the cam/crank to go out of time. Drained engine oil and found bearing material. We also cut oil filter open and found more bearing material. The timing cover was removed and verified the cam timing was off. In conclusion the engine has failed and will need full replacement. This is the exact failure mechanism under active the federal safety agency Investigation EA26005.

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 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 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

Filed Sep 18, 2026 · Engine, Suspension · UT

Both of my upper ball joints wore out and one broke as I was driving down the road at 65 miles an hour pulling me into the on coming lane of traffic, there was no warning of this. I had both upper and lower ball joint replace. If there had been another vehicle coming in the on coming lane we would have had a head on collision. At an earlier date the motor in this same truck had a fallen lifter which cause my motor to loss power, I was able to take it to the local GM dealer and they fixed it, there was no warning this was happening either. I am worried I will have a catastrophic engine failure and GM will not cover this. I have looked up my

Filed Sep 18, 2026 · Engine · AL

While driving 40 MPH my entire dash lite up with every known light and the vehicle lost all power. The dealer stated I need an entire engine replacement, as with Many 6.2. My vehicle is 1 months out side of the recall, it has the exact symptoms and the exact damage as the recall.

Filed Sep 9, 2026 · Engine · MO

Coolant Control Valve failure. This vehicle year is included in a GM bulletin that extends the Coolant Control Valve replacement coverage to 150K miles due to a faulty design. My is valve failing exactly as described in the bulletin and GM will not cover the replacement due to my vin number. The vehicle randomly goes into reduced power whereby it is prohibited from safely keeping up with traffic. Research shows that there are a significant number of owners in my same situation where GM is denying repair and replacement coverage.