GMC Sierra 1500 transmission problems

POWER TRAIN

Transmission shifting hard in first few gears and only 87,000 miles on Transmission.

NHTSA complaint #11764196 — an unverified report by a vehicle owner.

POWER TRAIN

The catastrophic power failure with no warning on my 2017 GMC Sierra, at 87450 miles completely contaminated the engine oil cooling lines with metallic debris and fractured structural mounts. The servicing dealership replaced the transmission but is refusing to remediate the engine line contamination without out-of pocket payment. The vehicle cannot be safely operated without causing terminal engine failure on the highway, creating a imminent mechanical and traffic safety hazard.

NHTSA complaint #11763735 — an unverified report by a vehicle owner.

POWER TRAIN

Power steering seems to be lost for a second or two at low speeds turning. Happens multiple times a day.

NHTSA complaint #11763463 — an unverified report by a vehicle owner.

POWER TRAIN

Purchased above listed vehicle new in XXX. Immediately noticed a 'coolant' smell in cab. brought vehicle in for coolant smell issue on XXX and XXX. We were told that there was no issue until finally on XXX we were told the radiator needed to be replaced at OUR expense. XXX we received a letter from GMC advising the "engine coolant control valve" may fail. In XXX while driving on mountain roads (we live in [XXX]) the check engine light came on and while at 50 mph, the vehicle went into "limp mode" we lost power and speed was immediately reduced. We now know that a symptom of that valve failure is coolant smell in the cab of the car, a problem we had attempted to address with GMC from the beginning. We could have had a serious accident driving on a busy mountain road when this failure occurred. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA complaint #11763393 — an unverified report by a vehicle owner.

POWER TRAIN

Truck rear wheels locked up while going between 45 - 50 mph nearly causing accident. Driver behind me had to lock-up their breaks to avoid collision. This is happening every time I drive the truck for more than 30 minutes. It is happening multiple times a day now. I cannot drive truck - too unsafe to drive. Tried getting serviced, but local GMC dealer said they are backed up with truck transmission issues and can't get mine in until Sep 15 - 3 weeks after first reporting. No warning signs. The locking of rear wheels takes me by surprise.

NHTSA complaint #11763465 — an unverified report by a vehicle owner.

POWER TRAIN

Powertrain issues and a chassis issue that is extremely dangerous.Tailgate on rare occasions falls open by itself. There is a design flaw in the placement of the catalytic converters. The heat is burning up the fluid. I could not believe my eyes when I serviced the transmission. This is another shortcut by GM to save on the extra wiring needed for the oxygen sensors (2)in the converters and the two oxygen sensors downstream of the converters. There is plenty of room for the converters further down by the tail shaft to drive shaft connections. This is GM’s way of being cheap. Here’s the problem. The converters get way too hot. The fill plug for the transmission which is behind a low rent heat shield crumbled into my hands from excessive heat buildup. GM knows there is a problem with the fluid breaking down. Their bandaid answer is to use Mobil 1 fluid instead of the recommended Dexron 6. What needs to happen is a safety recall issued for the unwanted tailgate deploying all by itself. There needs to be a redesign in the exhaust system. The Transmission (8 Speed) has a catalytic converter exactly on both sides and the crossover pipe runs directly under the transmission sump pan. No wonder they are having issues with transmissions burning up. THIS IS A FIRE HAZARD !!! With the converters being so close to the exhaust manifolds, a leak from the engine or the transmission would be enough to ignite and possibly kill the occupants. All in the name of saving a few cents in wiring. Myself, I am a retired GM Mechanic. I started working at Sewell Cadillac in [XXX] in 1975. I have held the title of ASE Master Tech. Cadillac Master Tech. I have been a GM Shop Foreman and A GM Service and Parts Director in my Career. I retired from Federal Express as in charge of Fleet Maintenance and GSE(Aircraft Equipment). I have certifications from Mercedes, BMW, Toyota, Commander Loaders, Goodyear, and more. Given the right set of circumstances, it could end very badly. Dangerous Truck ! INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INF

NHTSA complaint #11763015 — an unverified report by a vehicle owner.

POWER TRAIN

After numerous attempts getting GM to finally look at why my vehicle because after the L87 engine swap, which failed after the Pico test and oil, oil filter, and oil cap change my truck has been dangerous to drive. It falls on its face when taking off or driving. It acts as if something is holding the truck back. It takes more throttle to get it moving. Then in traffic while moving it randomly lunges forward very quickly as if I have the gas pedal to the floor. I came very close to rear ending a Deer Park police vehicle. They told me to get my own alternate transportation and they would then look at it. I had to go out and get a rental car. I had no choice. I explained due to my HIGH medical bills following a cancer diagnosis, I could not afford a rental and my appointments. They basically told me come see them when i can make my arrangements. So, i rented a car, took the truck in, four days later i was told that the problem was my ADAS camera. I told them it worked fine before yall had it 3 months waiting on an engine. They told me I would have to pay around 1000 dollars to have my truck repaired. Even though it was clearly something they did. I made arrangements to pay them. I picked up my truck. That evening I was happy. Well, the next morning while going to get coffee the problem returned. I took it back to the dealer. I was again told, go get another rental and leave it here. I have done that. Well, that week went by. I had to borrow money to get the rental for another week. So, i could make it to my cardiologist today. I have to get cardiac clearance before i begin surgery Oct. 1st. Between now and then, i have an appt with pain mgmt., A PET scan, and an Echo/Doppler for cardiac clearance. Surgery begins Oct. 1st. This has been making it very difficult to manage appts. with Gastrointerology, Cardiology, Oncology, Infusion services, Pain mgmt., Therapy with a Psychiatrist, My new Esophogealist (for surgery). And follow-ups and blood tests. This is ongoing.

NHTSA complaint #11763190 — an unverified report by a vehicle owner.

POWER TRAIN

Lifters and camshaft failure, loud clanking, & sudden power loss on the 6.2 motor are the first noticeable signs. Instantly when everything happened check engine light, cruise control, & stabilizer lights flashed. The sudden loss of power forced the vehicle to suddenly slow down forcing my camper into the truck. I was hauling a within weight standerd camper but had difficulty bringing both the truck with the camper to a safe stop. There were no early signs or signal prior to sudden cautostrophic engine failure & all service records have been completed by a GM certified service dealer.

NHTSA complaint #11763115 — an unverified report by a vehicle owner.

POWER TRAIN

I HAD COMPLAINED TO THE DEALER LESS THAN ONE YEAR AFTER PURCHASE IN MAY OF 2019 THAT THERE WAS A SHUDDERING NOISE AND THE TRANSMISSION HESITATES AND SEEMS TO LOCK UP AT TIMES. I WAS TOLD IT WAS "JUST HOW THE 8-SPEED TRANSMISSION OPERATES". IT HAS CONTNUED THROUGHOUT OWNERSHIP AND NOW SEEMS TO LOSE POWER AND VIBRATES EXCESSIVELY DURING ACCELERATION.

NHTSA complaint #11762906 — an unverified report by a vehicle owner.

POWER TRAIN

Transmission failed, Value Body is listed by dealer as the cause. GMC is saying that my vehicle is not part of the recall, even though it is part of the same model, same years as well as the same problem, the value body on the transmission. See estimate from dealership Tucks GMC Hudson, MA TRANSMISSION REPLACEMENT WITH BYPASS VALVE $6800.00 RADIATOR REPLACEMENT LEAKING $1980.00 ABS TRACTION LIGHT WHEEL SPEED SENSOR $395.00 CHECK ENGINE LIGHT IS ON NEEDS PCV VALVE HOSE AND SOLENOID $430.00 OIL LEAK BETWEEN ENGINE AND TRANSMISSION ?

NHTSA complaint #11762717 — an unverified report by a vehicle owner.

POWER TRAIN

I own a 2018 GMC Sierra 1500 V8 5.3 liter which is at 46, 433 miles. Over the past few weeks I have noticed the transmission having difficulty shifting in first gear and lurching, and making shuddering noises, and as well making a constant ticking noise. After an experienced mechanic had put a diagnostic system onto my truck, his system diagnosed a Transmission Lifter Failure, specifically 2 out of the 8 lifters. A few days later (9-04-26) I took my truck to a certified GMC servicing business (Patriot Chevrolet of Hopkinsville KY 270-886-1207) and had a transmission servicing done. I had told the Customer Service representative Amanda Williams about the ticking and that I thought 2 lifters going bad in the transmission were the source of it. 3 hours later the servicing was done which cost $ 474.43. She did not know if the ticking had stopped or not. I started my engine to head home and the ticking was still happening. Nothing had changed. I got home, parked and have not started the engine since to minimize any further damage. I have become aware that this year, make and model has become infamous for the engine/transmission design and parts failure which has been at the center of thousands of class action lawsuits. I have owned this vehicle since inheriting it from my late father for 2 months before he developed dementia and suffered a broken hip. I have religiously had the oil changed every three months regardless of the mileage, and this is a sealed transmission which cannot be worked on by someone but a certified GMC mechanic, which wasn't a worry because the truck's manual says doesn't need to be worked on unless there seem to be problems. Which is what I did on 9-4-26, hoping that a servicing would fix the issue. During the 5 years that I have owned this truck, I never received ANY sort of notice from GMC that might've hinted at possible Transmission Failures, though GMC has been totally aware of. Sudden power loss dangerous and unfairly expensive to drivers.

NHTSA complaint #11762401 — an unverified report by a vehicle owner.

POWER TRAIN

Within the first 3 years of purchase as a new vehicle, my 2018 GMC Sierra Denali equipped with the GM 8L90 automatic transmission developed a pronounced judder during light acceleration, resembling driving over rumble strips. The condition was first reported to an authorized GMC dealer on October 23, 2021, at 26,648 miles while the powertrain warranty was in effect. GM authorized a transmission-fluid exchange from the technical service bulletin (TSB) 18-NA-355, dated April 2020, but that repair did not provide a lasting correction. The condition continued, and in 2026 the authorized dealer diagnosed an “internal stator issue causing judder on light acceleration” and recommended replacement of the torque converter. We completed the repair and retained the removed converter. The defect affected the vehicle while accelerating and created concern about predictable power delivery when merging, entering traffic or crossing an intersection. Continued torque-converter malfunction can generate heat and debris, damage the transmission and potentially impair acceleration or power transfer. GM had issued technical bulletins addressing torque-converter shudder in 2018 Sierra vehicles before this truck was purchased, but there has been no recall. I request that NHTSA evaluate whether this recurring defect presents an unreasonable safety risk in GM vehicles equipped with the 8L90 transmission.

NHTSA complaint #11762122 — an unverified report by a vehicle owner.

POWER TRAIN

The contact owned a 2026 GMC Sierra 1500. The contact stated that while slowly driving up a slightly inclined driveway and making a left turn, the engine shut off. The contact stated that either the parking brake activated, or the vehicle suddenly decelerated. The contact stated that the failure had occurred several times, with three identical vehicles, including the loaner vehicle provided by the dealer. During the failure, the messages, "Press Start" and "Service Transmission" were displayed. The vehicle was taken to the local dealer who was unable to determine the cause of the failure. The vehicle was not repaired. The vehicle was later traded in for an identical vehicle. The manufacturer was notified of the failure.

NHTSA complaint #11762072 — an unverified report by a vehicle owner.

POWER TRAIN

The contact owns a 2026 GMC Sierra 1500. The contact stated that while driving at an undisclosed speed, the transmission independently shifted to park or neutral. The contact stated that the failure had occurred while driving at slow speeds. The contact stated that during one failure, the brakes independently activated, and the vehicle shut off. The contact stated that while attempting to restart the vehicle, the vehicle started. The contact stated that the failure was persistent. The dealer was made aware of the failure by phone. The vehicle was taken to the dealer; however, the diagnostic result was not provided. The failure mileage was approximately 500.

NHTSA complaint #11761844 — an unverified report by a vehicle owner.

POWER TRAIN

The contact owns a 2026 GMC Sierra 1500. The contact stated that while slowly driving up a slightly inclined drive port and making a left turn, the vehicle shut off and the parking brake was activated or the vehicle suddenly decelerated. The contact stated that the failure had occurred on several occasions with three separate identical vehicles, including the loaner vehicle provided by the dealer. During the failure, the messages "Press Start" and "Service Transmission" were displayed. The vehicle was taken to the local dealer who was unable to determine the cause of the failure. The manufacturer was notified of the failure. The failure mileage was 29.

NHTSA complaint #11761966 — an unverified report by a vehicle owner.

POWER TRAIN

I am reporting a serious safety concern involving a 2023 GMC Sierra 1500 Denali, 6.2L L87 V8, VIN [XXX]. This vehicle has now experienced two catastrophic powertrain failures at very low mileage. The first catastrophic engine failure occurred at approximately 23,696 miles. The vehicle was taken to a GMC dealer, where the repair documentation states that the engine had suffered significant internal damage, including damage to the #3 connecting rod, a missing connecting-rod bearing, bearing material throughout the engine, and a scored crankshaft. The dealer determined that the engine was seized and required replacement. GM replaced the engine under warranty with GM engine assembly part number 12740076. The vehicle has now experienced a second catastrophic failure. On [XXX], while traveling approximately 40 mph, experienced grinding, lurching, and knocking, followed by a complete loss of propulsion. The truck would no longer move and had to be towed to a GMC dealer. At the time of the incident, no warning lights or warning messages were observed. The transmission is also suspected to have failed, although the exact cause and extent of the transmission failure have not yet been determined by the dealer. I understand that NHTSA is currently investigating failures involving GM 6.2L L87 engines, including failures occurring after previous recall remedies and engine replacements. I am therefore requesting that this incident be included in NHTSA’s investigation and considered when evaluating the effectiveness of the existing recall remedy and the safety of replacement L87 engines. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA complaint #11761755 — an unverified report by a vehicle owner.

POWER TRAIN

Automatic Transmission not shifting properly unable to accelerate bangs gears while shifting noises from the transmission not reported no warning lamps

NHTSA complaint #11761343 — an unverified report by a vehicle owner.

POWER TRAIN

While driving truck jolts (rear wheels lock up) then downshifts into a lower gear. Appears to be similar issue as described in Recall 24V797 and 25V148. Not sure why my VIN does not show up on recall. Based on description it is the same problem. Feels unsafe to drive.

NHTSA complaint #11761258 — an unverified report by a vehicle owner.

POWER TRAIN

I am reaching out to NHTSA due to a vehicle that I believe will get me and/or my family in a major accident and cause serious injury or death. The vehicle that I had purchased in 07/08/2025 had a clean history report and was bought at 54,587 miles. It started having issues 8,563 miles later (odometer reading 63,150 ) on a trip that was 400 miles round trip. I was driving the vehicle on a highway at 65 mph and i felt a knocking vibration in the pedal it was not long before i could even pull over when the engine throttle had completely lost power causing the vehicle to almost come to a complete stop immediately having to steer onto the shoulder. after failing with no check engine light or warning present during the use of the vehicle on the road. it was giving off high temp/engine overheating with the engine making a continuous knocking sound in the engine. It eventually seized to work completely not being able to shift into neutral to push, and had to get it towed to the dealership 204 miles away. GM had advised the dealership to replace the whole engine which they did, and that second engine had given out 678 miles later (odometer reading 63,828.) I am now on my THIRD engine and i cannot trust or rely this vehicle for saftey or transporation. i have reached out to GM to file a claim and attempt to adress this issue to try and come to a resolution, however they denied my claim and have said that i am not "eligible" for a buyback program. I am considering getting legal attorney this is very frustrating to say the least GM is a terrible manufacturer for this issue

NHTSA complaint #11761466 — an unverified report by a vehicle owner.

POWER TRAIN

Engine went out very devastating $10k out of pocket

NHTSA complaint #11761078 — an unverified report by a vehicle owner.