GMC Complaints

Driving to the lake on the highway towing a trailer, a loud tapping noise started followed by vibration. Engine seems to have lost power during acceleration.

ON THE INTERSTATE THE TRUCK SAID TO PRESS ENGINE START AND EVERYTHIG WAS DEAD, I WAS ALMOST HIT SEVERAL TIMES TRYING TO GET IT FROM THE PASSING LANE TO THE EMERGENCY LANE. I TOWED IT TO MY DEALER WHO SAID THE ENGINE SUFFERED CATASTROPHIC FAILURE DUE TO A RECALL ON THE 6.2 ENGINE. NO WARNING LAMPS OR ANY INDICATORS WERE GIVEN. ALL SERVICE RECORDS ARE IN ORDER ALONG WITH A RECALL INSPECTION RELATED TO MY ISSUE.

The main issue is the transmission... It shudders. Now I have to change the oil every 10K miles on it, or it will start shuddering again. It first started when the truck had 50K or a little more miles in it. The issue was resolved, I thought... Then it did it again at 69K (Just out of the warranty). I called the dealership and they stated I had to pay if I wanted an oil change, and they could not do an oil flush even if I paid for it. So I said OK, I will take it to a mechanic, and I did and "fixed" the problem. I used the oil GM recommended and the shuddering stopped. BUT then, another 10K miles and it starts again. I have changed the oil a lot of times... It now has 128K miles in it, and this last time, I had to change the oil at 9k miles because of the shuddering... What will be next? I will have to change it at 5K miles, just like the motor oil? It is sad to see all these people having the same issue as I do, and GM does not do anything about it. I've done a lot of research... There is a guy that fixes the issue eliminating a specific valve, in the transmission, and updating the other ones with higher quality valves they make to fix the problem. I'm sure it would cost GM some money, but these trucks are expensive, you know? It is sad that no one is trying to help consumers when companies sale these cars and trucks to the public for a very high price and they do not take care of the mistakes they make when producing them. Please help us making GM fix this transmission issues. It is not fare for us consumers to be having trouble with new vehicles. Thank you for your time.

I have a 2023 GMC Sierra HD3500 6.6 Duramax. February of 2025 the valve body failed after 23,000 miles. The failure happened when the transmission had an extremely hard shift at 55 mph and then went into 5 gear limp mode. Computer through code P0700 and P0747. The P0747 is the code that tells you the valve body failed. When I took the truck to the dealer, they would not let me take the truck home because of the high risk of the transmission locking up and causing bodily injury, aka crash. Since the valve body was back ordered, I was warmed that it may be a month to get a replacement and install it. I finally got the truck back after 33 days. To add to the frustration, GM would not give me a loaner truck. They would give me a loaner SUV but that did not have what I needed out of a vehicle.

Vehicle passed initial inspection and had higher viscosity oil installed. After driving for the past six months I noticed a burning oil smell inside the truck. The smell gets intense at times especially during highway driving. The OW-40 viscosity oil is causing high fumes within the cockpit. Please consider checking this issue out during your added investigation into the L-87 engine failure. I shouldn't have to drive with the windows down but I do. I will have the truck inspected during my next oil change next week.

The transmission made a loud noise, resulting in a sudden decrease in speed while driving in traffic. Felt similar to being rear ended in a collision. The lights came on in my dashboard including the check engine light. Tried driving the vehicle and it would shift erraticaly rendering un-driveable. Had to be towed to my GMC dealership for service. The initial diagnosis is an issue with the "valve body". a quick search on the internet presented several other users with this issue in this model truck with this transmission. The service department also seemed to be aware of the issue. If it is so widely known, why would there not be a recall placed on these vehicles? I'm glad I had already dropped my son off at school and that I was not on a Main Street where I could safely pull over and wait for the AAA driver.

About 2-3 months ago I had a battery swell up and start smoking and making an awful smell in my truck. I took it to dealership and was informed that I needed a new battery and it was not covered under bumper to bumper warranty or my extended warranty which I thought was ludicrous. The truck is 18 months old. It does have 50,000 miles but I have yet to see one that isn’t at least prorated for five years. So fast forward to today and the other battery starts doing the same thing except this time my lights are going crazy. Brights on and off and on and off. I get back to my camp and the battery and wiring is smoking like crazy. I towed it to the shop. It’s been in there two weeks and the only thing they tell me now is that I need 2 new batteries and that’s all they can do until I agree to pay for the other one that isn’t under warranty (because I already paid 300 to change 1st one it’s under warranty for 5 years). So I told them to do it. It’s been there two weeks and not a damn thing has been done. Not even installed a new battery. I know because I went yesterday and they couldn’t open my tailgate to get my tools out. Probably the last GMC I purchase.

My 2020 gmc sierra has had poor gas mileage problems i have taken it to gm a few times with them not able to dind anything wrong through diagnostic. A couple years later my horrible gas mileage came back and service ecs and stabilitrack message came back on and disappeared. I spoke to another shop and they advised me its the dfm lifter issues that everyone has been talking about. So the shop performed the well know fix and has fix the issue. A month after now the valve body gave me a p2817 code showing that the solenoid is stuck in the off and was also advised that this is a know issue being addressed. Currently the truck is in the shop. When is enough enough with all the issues across the nation whwn is gm going to make it right

Setting in a parking lot and the tailgate fell open and hit another car. The tailgate was closed and has fell open 3 more times while the vehicle is in park and one time it was powered off.

Truck began idling very rough. Went straight to the dealership. They shut the truck off and it would not restart. No CEL or messages on the dash. Tear down reveled a failed exhaust valve in cylinder #4. Truck has 10,000 miles. A replacement engine has been ordered under warranty. Luckily, we happened to only be a few miles from a dealership when the failure happened. There was no warning, no prior symptoms what so ever.