GMC Complaints

Vehicle suddenly lost power without warning or engine light coming on. Vehicle was inspected and found that the transmission fluid pump failing caused low transmission pressure and replacement was required. 70k transmission fluid change was done per maintenance recommendations. Vehicle had 112k miles.

I am the original owner of a 2014 GMC Sierra 1500 (VIN: [XXX] ) and began experiencing serious mechanical and electrical issues while the vehicle was still under warranty around 40,000 miles. These included engine RPM fluctuations at idle, vibrations under acceleration above 65 MPH, and intermittent misfiring — all symptoms that are now believed to be early indicators of defective lifters or valve train components. I also experienced repeated electrical failures including a rear turn signal malfunction due to melting/corroded taillight sockets, a thumping rear-end noise, differential knocking, and body panel issues (hood lifting at highway speeds). These were reported multiple times to authorized GMC dealers (Mike Haggerty GMC and Rizza GMC), but I was told there was no issue or no repairs were made. GM refused to assist when I escalated the issue in 2017 via a detailed email, despite all problems occurring within the warranty period. I’m now dealing with a persistent ticking sound from the engine and loss of power, which matches widespread reports of lifter failure in GM’s 5.3L/6.2L V8 engines. These failures pose both a mechanical and safety risk due to stalling, misfiring, and potential electrical fires (in my case, from a failed taillight socket). A class action lawsuit ([XXX], et al. v. General Motors LLC) has been filed regarding these known defects, yet GM has not issued a recall. I’m filing this complaint to add my case to the record and urge NHTSA to investigate these issues. I have full documentation of the original complaint and am willing to provide it upon request. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

I have taken it in due to engine mounts 4 different times, transmission replaced and in October 2024 I took it in for issues I was experiencing like I had before my transmission went out. I did not get my truck back until almost Dec 2024 and that was due to there employee backing into the front end of my truck. So after all that my warranty was up Dec 24 2024 and then on April 16th 2025 I was driving my 2018 GMC Sierra 6.2l 1500 Denali 129,600 miles at approx 30 mph it was late so the streets were empty and we started to hear a knocking or what I thought at the time was a very bad exhaust leak. We parked and then we started to try to make it home very slowly which we did and it was not making to much noise. The next day I called GMC and explained they said bring it in. I towed it there to be safe but it did start and still ran at very slow speed. They called me and said that the lift side rockers/ lifters 1 failed and it was stuck due to a misfire and that the engine would need to be rebuilt and sent me over some very vague break down which looked like a lump sum price. I requested and better break down and got a screen shoot and that when he said that’s the best they can do. There were no engine lights on or warnings nothing at all. It also just got serviced at GMC for an oil change on February 27th 2025 along with some air filters. Today is April 29th and still waiting for the service manage to call and see if they can do anything to help out instead of charging full price. I will Attach pictures of the cost break down if possible. Thank you

I purchased a MagnaFlow aftermarket catalytic converter system for my 2008 GMC Yukon SLT 5.3L through Walmart’s online marketplace, sold by a third-party vendor called OurDealsRock. The product was advertised as “50-state legal” and compatible with vehicles registered in New York State. However, shortly after installation, my check engine light turned on, and diagnostic codes P0420 and P0430 (Catalyst System Efficiency Below Threshold) appeared. Initially, I thought this was a minor sensor issue, but over time, the vehicle’s performance gradually deteriorated. I noticed reduced acceleration, poor fuel economy, and eventually significant loss of power. The vehicle began shaking under load, misfiring, and overheating. These symptoms worsened steadily—not immediately—but progressively after continued driving with the aftermarket converter installed. I had the vehicle inspected by a certified mechanic, who confirmed that the MagnaFlow converter was not CARB-compliant, was not approved for use in New York, and that it had been illegally marketed as such. He also informed me that prolonged use of a non-compliant, malfunctioning converter caused excessive backpressure, leading to complete engine failure over time. The diagnosis was confirmed by a second mechanic before I committed to the engine replacement. The product was later removed from Walmart’s site, becoming unavailable for sale in my zip code [XXX] ) shortly after my initial complaint. This shows clear acknowledgment that it should never have been sold to a New York consumer in the first place. But by the time it was taken down, the damage had already been done. Component/system that failed: •MagnaFlow aftermarket catalytic converter system •Ultimately caused failure of the vehicle’s engine block Safety concerns: •My family and I were unknowingly driving with a damaged and failing engine •The vehicle’s degraded performance, overheating, and power loss could have compromised our safety during highway d INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORM

I have had major transmission failure in my 2021 GMC Yukon Denali (6.2L V8, 10-speed automatic). The vehicle has approximately 72,000 miles. Recently, a critical internal clip/retainer in the transmission broke loose, sending metal debris throughout the transmission. This catastrophic failure has rendered the vehicle undrivable and requires a complete transmission replacement. Unfortunately, the vehicle is just outside the powertrain warranty, yet I firmly believe this failure is due to a manufacturing/design defect – not normal wear and tear. I purchased this Yukon Denali as a premium, flagship SUV and have maintained it carefully. I expected the transmission to last well beyond 72k miles under normal use. It is disappointing and that a core component failed so early. Not only has this imposed a significant financial burden, but it also undermines my confidence in the vehicle’s safety and reliability for my family. A modern transmission should not self-destruct at this mileage, especially given GM’s reputation and the Denali’s top-of-the-line status. Importantly, I have discovered multiple known issues and GM bulletins related to the 10-speed automatic transmission used in my Yukon. For example, GM issued a major recall in late 2024 (NHTSA Campaign 24V797000, GM recall #N242454440) affecting 2021 Yukon models (among others) due to a defective transmission control valve that could fail and cause the rear wheels to lock up, this demonstrates that GM has acknowledged serious problems in the 10L80/MQC 10-speed transmission design. Additionally, a recent GM service bulletin (PIP6008C, Jan 24 2025) indicates that internal transmission retaining rings can dislodge, causing the internal gears to separate – which leads to loss of reverse and internal damage. This scenario is similar to what happened in my transmission. My family was left stranded away from home with no warning. The vehicle just stopped working. The warning lamp did not come on until diagnostics was run.

I wanted to reach out to see if there is anything in addition to the lemon law. I bought a 2021 GMC Sierra with 38,000 miles on it around March of last year. There was a motor defect which was covered by the warranty. I was driving and it stopped in the middle of the road so I had to safely maneuver out of the main road. The truck was towed to my house with 45,184 miles on it, until the GMC dealership could take it in to inspect. They did take a while to get me a rental because everything was backed up. They said they could rent me out a truck due to not being their brand and that it only covers a certain amount. It got taken in by the dealership on 7/15/2024 and ended up getting the truck back repaired on 8/27. I did get the truck back and have been having it, I am just worried about it breaking down or anything of that nature. I just wanted to know if there is any further process I should do or since they repaired it there should be no issue.

Backup camera failed. Same issue on 2021 Acadia SLT Needs to be investigated on 2023 models

Engine 6.2 liter needed to be replaced. Connecting rod and the engine froze up.

Driving down highway. Engine failure, loss of power. Ended up being lifter and camshaft failure.

2 months ago our 16 gmc Yukon Denali 6.2 bent a push rod on cylinder 4 . So had to fix it when I took out DOD lifters put them on work bench and about 10 minutes out the DOD lifters flew apart and know having transmission issues it’s starting to shudder ! So I would liked the [XXX] thing recalled because engine still isn’t right either it only has 130000 miles. I’ll never buy a [XXX] gmc because of problems! I want the [XXX] thing fixed ASAP we paid to much money for it to be having problems!!!! Please send a recall letter to fix it ! [XXX] . 4/29/2025 6:53 p:m INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)