2026 GMC Sierra 1500 transmission problems

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Vehicle: 2026 GMC Sierra 1500 AT4 (3.0L LZ0 Duramax Diesel) Current Mileage: ~16,500 miles Check Engine Light Status: NO Check Engine Light active Description of Incident & Symptoms: •Interstate Incident: While driving at highway speeds, a severe drivetrain vibration occurred (felt like a rear wheel weight flew off). •Dashboard Warnings: Within 5 minutes, intermittent "Traction Control" and "Forward Collision Warning" alerts appeared on the dash, accompanied by a sudden drop in engine power. •Engine Noise & Idle: Once safely pulled over, the engine exhibited a loud mechanical knock and a very rough, unstable idle. •Extended Crank: After shutting the engine off and waiting a few minutes, restarting the truck took roughly twice as long as normal (long crank/delayed start)

NHTSA complaint #11758123 — an unverified report by a vehicle owner.

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The contact owns a 2026 GMC Sierra 1500. The contact stated that while her husband was driving approximately 10 MPH, the vehicle unexpectedly shut off and independently shifted into park(P). The contact stated that previously, while the vehicle was idling in a parking lot, with air conditioner activated, the Auto START/STOP feature engaged, and the vehicle shut off. The message “Service Transmission” was displayed. The vehicle was taken to a local dealer and was diagnosed with transmission failure. The vehicle was not repaired. The manufacturer was not contacted. The failure mileage was approximately 2,000.

NHTSA complaint #11755200 — an unverified report by a vehicle owner.

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I am submitting this complaint to report what I believe is a serious safety-related defect involving the General Motors 6.2L L87 V8 engine installed in my 2026 GMC Sierra Denali. On July 10, 2026, while driving on a public highway near Bogata, Texas, the engine suddenly began making severe mechanical noises before catastrophically failing without warning. The engine seized completely while the vehicle was in motion. At the time of failure, the truck had only 13,517 miles. The sudden loss of engine power left my wife and me stranded on the roadside. Had this occurred while crossing an intersection, merging into traffic, passing another vehicle, towing a trailer, or traveling in heavier traffic, the consequences could have been far more serious.

NHTSA complaint #11755053 — an unverified report by a vehicle owner.

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When going up my 5% grade driveway the truck has slammed into “park” while moving two times. The car turns off as it slams into park and a “ service transmission” warning is on the dash. It leaves small skid marks from doing this while moving. It has 1790 miles on it. Dealer has had it a week and says they cannot duplicate the issue. Google search seems to indicate many trucks have had the same issues going up an incline.

NHTSA complaint #11752469 — an unverified report by a vehicle owner.

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While driving on the highway, the steering became much more stiff, and then I heard metallic clanging sounds for a few seconds. The dashboard said press start to start Vehicle. I pressed start while going 30 miles an hour and all lights and instrument clusters went black. I pulled into the grass median where the truck would not start or shift gears. Truck was towed to a GMC dealership

NHTSA complaint #11740289 — an unverified report by a vehicle owner.

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Transmission Cooler line blew out

NHTSA complaint #11738215 — an unverified report by a vehicle owner.

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I bought the truck brand new from Gregg Young in Atlantic, IA. While an hour into the drive home, the truck began shuttering as if the transmission was having problems finding the gear. I immediately made an appt with their parent dealership of Gregg Young in Plattsmouth, NE. They had the truck for a week and couldn’t duplicate the transmission issues after I reported several occurrences and symptoms, they also didn’t provide a service invoice of the work performed while I found was unusual. As I was driving the truck home from repairs it started hesitating and having difficulty finding gears. I didn’t think much of it since the dealer claimed there was nothing wrong. This past weekend while going 65 mph down the freeway the transmission started shuttering as well as the truck and the tires began to lock up to the point of almost losing control, there was also metal on metal noises. I had to pull over and luckily driving real slow I made it home. The Gregg Young dealership were I bought it will take no responsibility and provided falsification since no service was provided nor upon checking app gps there was no indications it left the dealership while in there possession for a week, will contact GMC in the AM since this has now become a safety issue and there was metal on metal contact noises and the serious risk of a crash.

NHTSA complaint #11732292 — an unverified report by a vehicle owner.

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ENGINE LOCK UP WITH 5018 MILES ON, IT IS A THE 6.2 MOTOR ROD AND CRANK BAD

NHTSA complaint #11730419 — an unverified report by a vehicle owner.

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The motor on my 2026 GMC Sierra stalled 2 weeks ago with a p0016(crankshaft position sensor issue). Was able to clear code and limp home. Vehicle did stall on a busy road and stop abruptly. Scheduled service and was advised to drive it in. Was experiencing irregular idle when warmed up, and a slight hesitation in the pedal. Service advisor started the vehicle and claimed no codes, and everything appear OK. Later in the afternoon the service advisor called to inform me that the vehicle had a siezed engine and had siezed during a test drive on the highway. Currently waiting on warranty information, and engine replacement information but i've been informed it will require a whole new engine. This is the same 6.2l L87 V8 that has been in near constant recalls from GMC over the last 6 years.

NHTSA complaint #11729317 — an unverified report by a vehicle owner.

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While driving at approximately 60 mph on an open road with no obstacles present and no braking input, the rear wheels spontaneously locked up without warning. No brake pedal input. No warning light prior to the event. No obstruction in the road. The vehicle has been subject to an active manufacturer recall for rear wheel lockup due to transmission control valve failure. The dealer's own diagnostic system generated a report showing six active fault codes in the following days including lost communication with the Brake System Control Module and Transmission Control Module. These codes were not addressed on the repair order. The dealer attributed the lockup to an Automatic Emergency Braking activation without diagnostic confirmation and performed no repair. The manufacturer's own internal bulletin dated January 22, 2026 acknowledges the exact fault codes present on this vehicle as a known defect. The dealer cited this bulletin to dismiss the concern while stating no problems exist. A persistent brake noise has been confirmed by two separate authorized dealers across three visits with no repair performed at any visit. The vehicle has required five dealer visits in 77 days of ownership with 1,729 miles. The defect remains unresolved and poses serious risk of loss of vehicle control at highway speed.

NHTSA complaint #11726026 — an unverified report by a vehicle owner.

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My engine seized up on me on the highway. I was stranded and couldn’t start the vehicle and it was freezing outside.

NHTSA complaint #11721299 — an unverified report by a vehicle owner.

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Vehicle stalled in busy intersection in McKinney Texas , unable to start are shift into a neutral position on transmission to remove from extreme dangerous intersection, sheriff advised that road side assistance that was contacted is not going to be in time (90min)to keep from causing an ongoing traffic backup , sheriff dispatched their own towing service to resolve the situation from getting extremely dangerous .vehicle and my wife was towed to McKinney Buick gmc dealership.

NHTSA complaint #11719035 — an unverified report by a vehicle owner.

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Odd noise from bell housing area at 1200 miles that went with engine rpm. Took the truck in to the dealer and they said they couldn't recreate it but to bring it back in if it returned. Jan 27th at 5200 miles on the truck, I was driving down the highway at 60mph and got a reduced acceleration message on the dash along with a check engine light. Brought it to the dealer and was informed it was a bad thrust bearing and needed and engine and turbo replacement. Still waiting for the truck to be done.

NHTSA complaint #11718072 — an unverified report by a vehicle owner.

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My 2026 GMC AT4 3.0L Duramax had a catastrophic engine failure on Sunday, February 8, 2026. It went into reduced acceleration and also fault code PO6DD. Thankfully I was not on a highway. The truck would not run over 45 MPH on flat ground, and then by the time I got it to a safe location 5 miles away it would not run over about 30MPH. This obviously resulted in the truck being towed to a dealership. I have been told the entire engine will be replaced. Upon further reading, I suspect this is a thrust bearing failure that is a well-known issue in this LZ0 Duramax engine. What I have read, this issue is occurring mostly on trucks built from May-Sept 2025, and my truck has a 7/2025 build date. This could have been major safety hazard if the engine had failed in a major freeway/highway.

NHTSA complaint #11717546 — an unverified report by a vehicle owner.

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I am submitting this complaint regarding a recurring transmission issue in my vehicle. The transmission consistently jerks and shifts erratically, particularly in the morning during initial operation when at cruising speeds of about 50-75 mph. This behavior occurs when the transmission temperature is below approximately 100°F and happens on a daily basis. The gear changes feel harsh and abrupt, kind of like it doesn’t know what gear to be in its raising concerns about both drivability and long-term transmission reliability. I brought the vehicle to an authorized dealership for inspection. After evaluating the issue, the dealer informed me that the behavior was due to the vehicle being in “Sport Mode.” However, this explanation does not resolve the concern, as the severity and consistency of the jerking appear abnormal and occur regularly under the same temperature conditions. Given the persistent nature of this problem and its potential safety implications — especially during acceleration and low-speed driving — I am requesting that this issue be formally documented and investigated. Thank you for your attention to this matter.

NHTSA complaint #11717655 — an unverified report by a vehicle owner.

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I heard a loud metallic knock that was not consistent with normal engine noise. I noticed the oil pressure was on the lower end of the scale but not abnormal based on how it is displayed. I decided to take the vehicle to the dealer ASAP for an oil change (that was coming due) and discuss with them. I drove roughly 20 miles from start of noise until delivery at the dealer. The truck gave me a "Reduced Acceleration, drive with caution" message 10 miles prior to the dealership but no associated lights, engine codes, check engine light or associated alerts on the myGMC app. Dealership found oil pressure ranging between 4-8 psi, and a failed oil pressure control solenoid, heavy metal debris in the oil pan including parts of the thrust bearing and oil squirter. Entire engine and turbo replacement was required. Truck had 143 hours on the engine and 6,300 miles. It was produced in August of 2025 with a purchase date of 17 October 2025. Produced: 8/25 Purchased: 10/17/25 Failed: 12/30/2025 Returned with new Engine: 1/23/26

NHTSA complaint #11712965 — an unverified report by a vehicle owner.

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2026 GMC Sierra Elevation X31 with 3.0 Duramax Diesel engine, 132-miles, thrust bearing 1.53-mm out of tolerance requiring engine and turbo replacement. Engine build date 25219 (07 AUG 2025), vehicle assembly date August 2025, purchased 10 OCT 2025, entered service for engine and turbo failure on 11 NOV 2025, returned 10 JAN 2026.

NHTSA complaint #11712398 — an unverified report by a vehicle owner.

POWER TRAIN

26’ GMC Sierra 1500 AT4 3.0l Duramax experiencing Harsh shifting occurring sporadically while accelerating and deceleration. More frequent and severe during quick deceleration. Severe clunking/rear wheel lock up while reversing. Very repeatable. Truck was a dealer demo and had 2400 miles on it when I bought it last week. Took it in to the dealer today and they said I need a complete new transmission.

NHTSA complaint #11711300 — an unverified report by a vehicle owner.

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My 2026 GMC 1500 is equipped with the 2.7L L3B & 8L90 Transmission. At approximately 1000 miles, I noticed that in 2nd between 2700-3200 RPM, a vibration could be felt throughout the cabin and would occur whether with or without throttle application. I am able to recreate the issue during hard acceleration or placing in manual mode. No matter the Vehicle mode selection (sport, normal, snow, tow/haul, etc.), the issue still persists. I took the vehicle to a local GMC dealer at approximately 6K miles to diagnose. I requested that we test drive another 1500 with the same 2.7L and Transmission. They brought out a 2026 Elevation Quad Cab with the 2.7L; less than 20 miles on the odometer.The same vibration was present in 2nd gear at same RPM band. I requested that the issue be escalated to a local GM rep. for further investigation. However the response from the dealer was inadequate and basically stated that no warranty work would be considered because it seems to be “normal operation”.

NHTSA complaint #11707315 — an unverified report by a vehicle owner.