2021 GMC Sierra 1500 problems

STRUCTURE:BODY

rear sliding window has plastic body seam that is broken allowing water to leak into the truck and cause mold and rust

NHTSA complaint #11756772 — an unverified report by a vehicle owner.

POWER TRAIN

Transmission Valve Body failure. - Caused wheels to lockup momentarily and killed the engine with sudden loss of propulsion. Link to video of incident: [XXX] INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA complaint #11756447 — an unverified report by a vehicle owner.

VEHICLE SPEED CONTROL

Push on accelerator truck barely would go, shifted hard, codes check engine lights flashing, engine sounded bad

NHTSA complaint #11756397 — an unverified report by a vehicle owner.

ENGINE

2021 6.2L GMC Sierra Denali. Has the L87 engine that is recalled but yet my truck doesn’t fall under the recall although the recall is for 2021-2024 engines. Everything that the engine recall states is the issue with my truck, I have service report from dealership stating that there is wear/breakage of cam shaft/crank shaft amongst other things including cylinder 3 and 5 misfiring , bearings broken , filings in the oil , banging in the engine and safety lights on. My local GMC dealership recommended that the only acceptable action was to replace the engine at my cost of course. This is unacceptable of a supposed reputable large corporation not caring about the “little guy”. The truck only has 136000 kms on it and I was only going 60 km/hr when this happened. Please help as I feel GM knows this engine is faulty but somehow has managed to escape a recall on my vin number

NHTSA complaint #11756392 — an unverified report by a vehicle owner.

VISIBILITY/WIPER

A small drip started approximately 18 months ago from top middle of left side window in rear slider. It was first mistaken as blow by from car wash. Leaking slowly progressed to dripping down middle of both side windows in rear sliders. Leaking progressed to drops coming from under headliner then dropping on side portions of rear slider. It then would drip onto seat or behind seats. Leakage was consistent with TSB 18-NA-383 as well as 20-NA-142 and 24-NA-103. In discussing with dealership, they recommended likely microfractures and sealant process called for in bulletins would likely resolve matter. As due diligence, spoke with independent glass shop to confirm. Glass shop indicated would not know until physically checked cracks/source of leak and looked for damage but based upon photos it appeared to be several frame fractures consistent with bulletins. I arranged rear slider replacement through independent shop. Upon pulling OEM slider, numerous stress cracks and fractures were noted. These included stain marks from water intrusion. Photos included showing original leaking as well as sample of cracks in original OEM plastic frame portion.

NHTSA complaint #11756237 — an unverified report by a vehicle owner.

POWER TRAIN

The contact owns a 2021 GMC Sierra 1500. The contact stated that while driving at an undisclosed speed, the transmission was shuddering, especially while driving uphill. The dealer was contacted, and the vehicle was diagnosed and determined to have a failure associated with a GM TSB for the incorrect transmission fluid inside the transmission reservoir. The vehicle was not yet repaired. The manufacturer was not made aware of the failure. The failure mileage was approximately 38,875.

NHTSA complaint #11754985 — an unverified report by a vehicle owner.

ENGINE

P1010 and P2B86 engine code, constant cooling fan on engine. Confirmed by dealership, quoted for coolant control valve. VIN not included in special coverage N252508341 for this known issue. Limited engine power alert, unable to maintain speed on highway. Dangerous condition traveling under speed limit.

NHTSA complaint #11753912 — an unverified report by a vehicle owner.

ENGINE

Engine temp rises way above mid-level and will stay there for several minutes before cooling back down to normal temps. 2 different mechanic shops have told me it's the coolant control valve, but want $2500 to fix it. This service bulletin is for the same year, make, model, and motor as my truck, but the dealership said it wasn't covered.

NHTSA complaint #11753949 — an unverified report by a vehicle owner.

POWER TRAIN

2021 Harley Davidson Sierra 4WD, 6.2L L87. Started the truck in the morning and immediately heard intermittent, very loud banging noise coming from engine. Shut truck down quickly and had it towed to dealer. Diagnosis was bent pushrods & failed lifters which were replaced under warranty. Factory warranty expired only 4 months after this failure, and the recall does not include my VIN so I did not get an extended warranty or any other protection. GM has yet to even reimburse the tow bill. Completely unacceptable for a truck that was well over $100k when new.

NHTSA complaint #11753693 — an unverified report by a vehicle owner.

ENGINE

2021 Harley Davidson Sierra 4WD, 6.2L L87. Started the truck in the morning and immediately heard intermittent, very loud banging noise coming from engine. Shut truck down quickly and had it towed to dealer. Diagnosis was bent pushrods & failed lifters which were replaced under warranty. Factory warranty expired only 4 months after this failure, and the recall does not include my VIN so I did not get an extended warranty or any other protection. GM has yet to even reimburse the tow bill. Completely unacceptable for a truck that was well over $100k when new.

NHTSA complaint #11753693 — an unverified report by a vehicle owner.

ENGINE AND ENGINE COOLING

The contact owns a 2021 GMC Sierra 1500. The contact stated that while driving approximately 70 MPH, the vehicle suddenly lost motive power, decelerated, and failed to properly accelerate while depressing the accelerator pedal. The check engine warning light was illuminated. After exiting the freeway, the vehicle stalled. The vehicle was towed to the residence and then later towed to the dealer for assistance. The contact was informed that there were metal shavings inside the engine oil. The contact was informed that the engine needed to be replaced. The vehicle was not yet repaired. The contact was informed that the VIN was not included in NHTSA Campaign Number: 25V274000 (ENGINE AND ENGINE COOLING). The contact stated that the vehicle had experienced the failure listed in the recall. The manufacturer was not yet contacted. The failure mileage was 149,000.

NHTSA complaint #11753444 — an unverified report by a vehicle owner.

ENGINE

CORRODED GROUNDING STRAP FAILED CYLINDER 5 GLOW PLUG CIRCUIT CRACKED AND SEPARATED EXHAUST BACKPRESSURE VALVE

NHTSA complaint #11753543 — an unverified report by a vehicle owner.

FUEL/PROPULSION SYSTEM

CORRODED GROUNDING STRAP FAILED CYLINDER 5 GLOW PLUG CIRCUIT CRACKED AND SEPARATED EXHAUST BACKPRESSURE VALVE

NHTSA complaint #11753543 — an unverified report by a vehicle owner.

ENGINE

The vehicle has about 38000. The warrantee expired about 6 months ago. About three weeks ago I started the engine, it sounded like a cement mixer filled with rocks. I had it taken to my dealer. They investigated the problem and determined that it has bad lifters and bent push rods. The dealer told me that it is a known problem but it is not covered by the current 6.2l engine recall

NHTSA complaint #11753048 — an unverified report by a vehicle owner.

STEERING

Vehicle: 2021 GMC Sierra SLT | VIN: [XXX] Dealership: Carl Black GMC Roswell, GA (11225 Alpharetta Hwy, 30076) | Invoice #[XXX] | Service Date: [XXX] Paragraph 1 – Suspension Hazard: Dealership diagnosed a worn left upper ball joint (popping sound on left turns) and installed Rough Country aftermarket upper control arms on my stock-height Sierra SLT. These arms are designed for lifted suspension and alter factory caster/camber geometry, placing extreme stress on ball joints. This can cause sudden ball joint separation, wheel collapse, and total loss of steering control at speed. The dealership admitted on the invoice they "could not find branding" on original parts and chose non-OEM lift components without my consent or any safety disclosure. Paragraph 2 – Brake Failure & No Safety Warning: The same service included a full front/rear brake job (pads + resurfaced rotors) using their certified technicians and parts. After pickup, the brakes failed to operate properly. When I returned, the service manager refused to correct their own workmanship and instead quoted $1,900 to repair the very brakes they just serviced. Most critically, at vehicle pickup they issued no written or verbal safety warning—no "do not drive" instruction—despite the brakes being knowingly compromised, endangering me and the public. Paragraph 3 – Requested Action: The service manager was unprofessional, condescending, and refused accountability. I request an immediate NHTSA investigation into Carl Black GMC's unauthorized use of lift-kit suspension parts on stock vehicles, failure to warranty their own brake service, and reckless omission of safety warnings at delivery. This dealership pattern poses an imminent public risk. Please escalate. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA complaint #11752674 — an unverified report by a vehicle owner.

SUSPENSION

Vehicle: 2021 GMC Sierra SLT | VIN: [XXX] Dealership: Carl Black GMC Roswell, GA (11225 Alpharetta Hwy, 30076) | Invoice #[XXX] | Service Date: [XXX] Paragraph 1 – Suspension Hazard: Dealership diagnosed a worn left upper ball joint (popping sound on left turns) and installed Rough Country aftermarket upper control arms on my stock-height Sierra SLT. These arms are designed for lifted suspension and alter factory caster/camber geometry, placing extreme stress on ball joints. This can cause sudden ball joint separation, wheel collapse, and total loss of steering control at speed. The dealership admitted on the invoice they "could not find branding" on original parts and chose non-OEM lift components without my consent or any safety disclosure. Paragraph 2 – Brake Failure & No Safety Warning: The same service included a full front/rear brake job (pads + resurfaced rotors) using their certified technicians and parts. After pickup, the brakes failed to operate properly. When I returned, the service manager refused to correct their own workmanship and instead quoted $1,900 to repair the very brakes they just serviced. Most critically, at vehicle pickup they issued no written or verbal safety warning—no "do not drive" instruction—despite the brakes being knowingly compromised, endangering me and the public. Paragraph 3 – Requested Action: The service manager was unprofessional, condescending, and refused accountability. I request an immediate NHTSA investigation into Carl Black GMC's unauthorized use of lift-kit suspension parts on stock vehicles, failure to warranty their own brake service, and reckless omission of safety warnings at delivery. This dealership pattern poses an imminent public risk. Please escalate. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA complaint #11752674 — an unverified report by a vehicle owner.

SERVICE BRAKES

Vehicle: 2021 GMC Sierra SLT | VIN: [XXX] Dealership: Carl Black GMC Roswell, GA (11225 Alpharetta Hwy, 30076) | Invoice #[XXX] | Service Date: [XXX] Paragraph 1 – Suspension Hazard: Dealership diagnosed a worn left upper ball joint (popping sound on left turns) and installed Rough Country aftermarket upper control arms on my stock-height Sierra SLT. These arms are designed for lifted suspension and alter factory caster/camber geometry, placing extreme stress on ball joints. This can cause sudden ball joint separation, wheel collapse, and total loss of steering control at speed. The dealership admitted on the invoice they "could not find branding" on original parts and chose non-OEM lift components without my consent or any safety disclosure. Paragraph 2 – Brake Failure & No Safety Warning: The same service included a full front/rear brake job (pads + resurfaced rotors) using their certified technicians and parts. After pickup, the brakes failed to operate properly. When I returned, the service manager refused to correct their own workmanship and instead quoted $1,900 to repair the very brakes they just serviced. Most critically, at vehicle pickup they issued no written or verbal safety warning—no "do not drive" instruction—despite the brakes being knowingly compromised, endangering me and the public. Paragraph 3 – Requested Action: The service manager was unprofessional, condescending, and refused accountability. I request an immediate NHTSA investigation into Carl Black GMC's unauthorized use of lift-kit suspension parts on stock vehicles, failure to warranty their own brake service, and reckless omission of safety warnings at delivery. This dealership pattern poses an imminent public risk. Please escalate. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA complaint #11752674 — an unverified report by a vehicle owner.

POWER TRAIN

On June 25, 2026, at approximately 84,000 miles, while traveling approximately 60-65 mph on Highway 121 in a posted 65 mph zone, driving my 2021 GMC Sierra 1500 AT4 equipped with the 6.2L L87 engine, multiple warning messages suddenly appeared, including “Check ESC,” “Check Parking Brake,” “Check Brakes,” and “Check Engine.” The engine began operating abnormally. I drove directly to Sewell GMC because I was concerned that the engine could fail or the vehicle could lose propulsion while in traffic. There was no crash, fire, or injury. Sewell GMC inspected the vehicle and confirmed catastrophic internal engine damage. The technician found metal debris in the engine oil and oil pan, damaged internal bearings, and camshaft/lifter damage. Sewell advised that the complete engine must be replaced. The vehicle remains at the dealership, has not yet been repaired, and the engine and failed components should be available for inspection. Before this incident, I had not experienced warning lights or symptoms indicating that an imminent catastrophic engine failure would occur. GM and the dealership advised that my VIN is not included in the current L87 engine recall because the engine was built in 2020. However, the diagnosed bearing damage, metal contamination, and catastrophic engine failure appear similar to the engine failures addressed by that recall. I am reporting this because an unexpected internal engine failure while driving creates a serious risk of loss of propulsion and a collision.

NHTSA complaint #11752087 — an unverified report by a vehicle owner.

ENGINE

On June 25, 2026, at approximately 84,000 miles, while traveling approximately 60-65 mph on Highway 121 in a posted 65 mph zone, driving my 2021 GMC Sierra 1500 AT4 equipped with the 6.2L L87 engine, multiple warning messages suddenly appeared, including “Check ESC,” “Check Parking Brake,” “Check Brakes,” and “Check Engine.” The engine began operating abnormally. I drove directly to Sewell GMC because I was concerned that the engine could fail or the vehicle could lose propulsion while in traffic. There was no crash, fire, or injury. Sewell GMC inspected the vehicle and confirmed catastrophic internal engine damage. The technician found metal debris in the engine oil and oil pan, damaged internal bearings, and camshaft/lifter damage. Sewell advised that the complete engine must be replaced. The vehicle remains at the dealership, has not yet been repaired, and the engine and failed components should be available for inspection. Before this incident, I had not experienced warning lights or symptoms indicating that an imminent catastrophic engine failure would occur. GM and the dealership advised that my VIN is not included in the current L87 engine recall because the engine was built in 2020. However, the diagnosed bearing damage, metal contamination, and catastrophic engine failure appear similar to the engine failures addressed by that recall. I am reporting this because an unexpected internal engine failure while driving creates a serious risk of loss of propulsion and a collision.

NHTSA complaint #11752087 — an unverified report by a vehicle owner.

ENGINE AND ENGINE COOLING

The contact owns a 2021 GMC Sierra 1500. The contact stated that while driving 35 MPH, the engine was making an abnormal sound, and the vehicle failed to accelerate. The engine was popping and making cranking sounds, with several unknown warning lights illuminated. The vehicle was driven back to the residence with the issues. The contact referenced NHTSA Campaign Number: 25V274000 (Engine and Engine Cooling); as a possible cause for the failure; however, the VIN was not included in the recall. The vehicle was taken to a dealer where it was determined that there was metal fragments found in the oil filter, and recommended that the engine be replaced. The vehicle was not repaired. The manufacturer was notified of the failure. The failure mileage was 50,000.

NHTSA complaint #11751500 — an unverified report by a vehicle owner.

ENGINE

I'm not sure if they've pulled it out yet. They said two weeks to get motor. Engine started shaking and then started knocking. Had wrecker take it to GMC dealer they said it needs an engine. It is a 2021 6.2 carbon pro 1500 Sierra AT4 it did not come up on recall list and I don't know why? it obviously the same problem.

NHTSA complaint #11751279 — an unverified report by a vehicle owner.

ENGINE

At 115,000 the coolant control valve has gone out. GM acknowledges this issues in 2020 model trucks. My truck is a 21 and displaying the same characteristics. A simple google search will show this is a known issue in 2021 vehicles as well. In 2020 model trucks GM has provided a special 150,000 mile warranty to replace this part. GM needs to step up and provide a proper warranty/recall for the affected 2021 models.

NHTSA complaint #11751124 — an unverified report by a vehicle owner.

FUEL/PROPULSION SYSTEM

P1098 code indicating stuck/ unresponsive engine coolant control valve. N252508341 exists for this part; however claim is my VIN is not covered under the bulletin or included on any standard warranty coverage. Part should last more than 150k miles, vehicle less than 90k. Less than 2 weeks ago suffered a complete EBPV failure that destroyed coolant and DEF lines, also not covered. No explanation for why my specific VIN (a 3.0L diesel in the supposedly covered MY) is excluded. Have been unable to find evidence of any applicable vehicles that were 'covered' under this bulletin. Fault forces an unexpected derate which can engage while accelerating, including while merging into freeway traffic. This is an obvious safety hazard. Engine check light illuminates approximately 30 to 60 seconds before derate limits top speed and throttle response. No messages to operator. Dealer has confirmed issue.

NHTSA complaint #11750814 — an unverified report by a vehicle owner.

POWER TRAIN

The 10 speed automatic transmission shakes and jumps between gears. The transmission also shakes and rumbles at cruising speeds. The diesel engine version of this truck is already recalled. My truck is a gas engine and should also be recalled. This is the same defective 10 speed transmission used in all GM vehicles and recalled in many. This vehicle needs to be recalled and fix before the wheels lock up and kill someone.

NHTSA complaint #11750566 — an unverified report by a vehicle owner.

ELECTRICAL SYSTEM

I am submitting supplemental evidence regarding my 2021 GMC Sierra (VIN [XXX]) for Recall Query RQ26001, Campaign 25V-274. Despite multiple repair attempts, my vehicle remains unsafe and non-compliant with GM Service Bulletin N252494002. The recall remedy was performed deficiently. [XXX] Northeast Buick GMC installed a remanufactured short block instead of the required complete engine, reused the original seized-engine oil pan (which continues to leak), and failed to address critical electrical damage. Documentation proves they deleted Labor Operation 14BUZ (Engine Electrical) after their technician noted a blown mega fuse. A second dealer, Penske Chevrolet, subsequently deleted Labor Operation 77CVZ01 from my repair order, demonstrating a systemic pattern of ignoring recall-required repairs. Electrical damage has cascaded, resulting in a burnt fuse block and active faults P0615, P0617, P26E4, P26E6, U0623, and U0284. More critically, within 24 miles of my last service, the vehicle developed a new, severe safety failure: the "Service Brake Pad Monitor" system failed, accompanied by a red "Service System" dashboard alert and a noticeably spongy brake pedal. These brakes were recently serviced, yet this failure introduces a new risk of crash not present prior to the recall "remedy." GM Executive Resolution Case XXX has provided no resolution, reimbursement, or safety assurance, ignoring all deadlines since XXX. I possess extensive documentation, including service orders showing deleted labor operations and diagnostic logs. I request this update be integrated into the investigation of RQ26001, as the current remedy is demonstrably ineffective and has exacerbated safety hazards. The manufacturer’s refusal to remediate these issues, despite my compliance, leaves me with an unsafe vehicle and significant financial loss. I am prepared to provide all supporting records to substantiate this complaint. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA complaint #11750329 — an unverified report by a vehicle owner.