2020 GMC Terrain transmission problems

Filed Sep 23, 2026 · Brakes, Engine · NC

While driving my 2020 GMC Terrain, I experienced a sudden loss of normal braking assistance. I had been traveling on the highway and exited onto a main road. As I approached a red traffic light at approximately 50 mph and attempted to brake, the vehicle would not stop normally. I was unable to stop for the red light and went through the intersection before I was able to safely get the vehicle off the roadway. Fortunately, there was no vehicle directly in front of me and I was able to make it through the intersection before any other cars, so no collision occurred. The vehicle was subsequently inspected and diagnosed by a GMC dealership. A diagnostic scan performed after the incident showed code P0556 for the brake booster pressure sensor circuit range/performance. The GMC dealership later diagnosed problems involving the vacuum pump, exhaust camshaft, and timing components and recommended replacement of the vacuum pump, exhaust camshaft, timing components, and related parts.” The sudden loss of braking assistance created a serious safety hazard and could have resulted in a collision, serious injury, or death. The vehicle is currently available for inspection.

Filed Sep 8, 2026 · Engine, Transmission · TX

Having the start stop issue on my terrain and recently over the last few months, it has been using oil everything that sounds exactly like the recall but mine is not included. My start stop is not working and I have to get him since it had only 60,000 miles on it years ago, but nothing was done.

Filed Aug 5, 2026 · Fuel system, Transmission · SC

Because of the intentional failure of GMC and there promise of “We are Professional Grade”, I almost got plowed down by a semi when the car began to quit on the highway going 60. After pulling into the next driveway, which happened to be a Parker’s Kitchen, and ending up on the curb spot, thanking God I wasn’t dead, I sat there for a moment wondering what just happened. As I went to restart the car, it wasn’t having any of it. 40,000 miles, not professional grade GMC, circus grade. Towed it to my home, figuring it has to be something minor and a diy fix. Bought the hyper-tough code reader delivered by Walmart and it delivered professional grade results: U18A2, P1787 and P187E. I am beyond pissed. I could have died due to your intentional negligence in manufacturing. I have a car that will not start, with payments. I have searched the internet and found your “save ourselves plan” and let’s do a voluntary recall starting with 2021 on the same failed parts I am dealing with at the moment. Thanks GMC, who is the ringleader of your circus?

Filed Dec 19, 2025 · Transmission · 104,000 miles · AR

The contact owns a 2020 GMC Terrain. The contact stated that while driving 35 MPH and depressing the accelerator pedal while driving uphill or making a left or right turn, the tires were skipping, and there was a clicking and whining sound coming from the front of the vehicle. There was no warning light illuminated. The contact stated that a friend test-drove the vehicle and informed that the vehicle had experienced transmission failure. Neither the independent mechanic nor the dealer was contacted. The vehicle was not taken to the dealer or an independent mechanic to be diagnosed or repaired. The contact related the failure to the federal safety agency Campaign Number: 20V668000 (POWER TRAIN); however, the VIN was not included in the recall. The manufacturer was notified of the failure and informed the contact that the VIN was not included in the recall. The failure mileage was 104,000.

Filed Dec 17, 2025 · Engine, Transmission · WI

The intercooler has been a document problem on GMC Terrains for awhile now. I had my intercooler replaced and now less than 10 months it is having the same problem. The vehicle will go into reduced power mode which would be a safety hazard because it will also stall sometimes when it is having performance issues. That could lead to someone colliding into me if it suddenly stops when someone is behind me. I believe this part should be recalled and fixed for free.

Filed Oct 8, 2025 · Transmission · 94,000 miles · CA

The contact owns a 2020 GMC Terrain. The contact stated that while making a turn, the transmission shifted into neutral and briefly lost motive power and stalled. No warning lights were illuminated. The contact was able to restart the vehicle; however, the vehicle failed to function while shifting to drive(D) or reverse(R). The contact opened and closed the door to see if the vehicle would reboot. After several attempts, the vehicle returned to normal functionality. The contact stated that on a separate occasion, the transmission was leaking transmission fluid. The transmission was constantly slipping. The check engine warning light was intermittently illuminated. The vehicle was taken to the dealer, where it was diagnosed that the START/STOP accumulator in the cap was missing bolts, which caused the transmission to fail. An unknown code was provided to the contact. The vehicle was not repaired due to the cost. The vehicle was taken to various independent mechanics who confirmed that the transmission had failed. The manufacturer was made aware of the failure. The failure mileage was approximately 94,000.

Filed Sep 2, 2025 · Engine, Fuel system · OH

I have been having intermittent problems for well over 1 year with my vehicle not accelerating. I try to accelerate from a stop, the vehicle does not respond. I have the accelerator pedal pressed to the floor nothing happens for 10-15 seconds, then vehicle will lurch forward and start responding. This has happened several times as I am pulling into traffic. Major safety concern that could cause severe injury or fatality. I also have other issues with vehicle not shifting gears, engine feels as though it is skipping while driving. I have taken this to the dealership and was told that they could not recreate the issue. No engine code or service lights have ever displayed. Dealership told me is can't be anything major since there are no codes or service lights. Currently have 72,000 miles, did purchase an extended warranty. I have seen many complaints of this same problem from other Terrain owners. GMC needs to fix this problem before someone is killed in a collision because their product won't accelerate.

Filed Jul 12, 2025 · Transmission · PA

I have been experiencing loss of power when going from a full stop to acceleration. I purchased my 2020 Terrain. I almost got in a car accident for the 3rd time today due to this loss of power issue. Stopped at a stop sign, I accelerate but the vehicle will barely move no matter how far down you push the peddle down. The loss of power is anywhere from 4 to 6 seconds then all of the sudden power will return. I've looked for recalls but there are none for my vin. This behavior is unpredictable and has occurred at stop signs, traffic lights, and when attempting to turn onto main roads. It has nearly caused accidents due to my inability to safely accelerate in time when merging or crossing traffic. I’ve read that GMC recalled certain 2021 and 2022 Terrain models for a fuel pump defect causing similar symptoms. My 2020 model is not currently included in that recall, yet it displays the same dangerous loss-of-power issue. I believe this is a serious safety defect that should be investigated and potentially included in the existing recall. I respectfully request that the federal safety agency investigate this issue further. I would also appreciate confirmation that this report has been logged. Vehicle Info: 2020 GMC Terrain VIN: [XXX] Engine: 1.5L Turbo Mileage: 62,142 Thank you for your time and your work in ensuring vehicle safety. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Jun 26, 2025 · Acceleration, Engine · PA

On 6/22/2025, brakes stopped working while trying to make a turn. Next multiple engines light came and car went into reduced speed mode. As I tried to find a safe place to stop, the vehicle went into limp mode and shut down in the middle of the road. The dealership said the issue was the vacuum pump which caused the timing chains to break. There have multiple recalls for this exact issue but my car is not on the list. My manufacture warranty ended on 5/21/2025. When I spoke to a GM representative I was told there was nothing they can do because there is not a recall for my vehicle. They explained even though I had the same problem the recall is for other vehicles. GM also issued a warranty extention on the vacuum pump to 10 years 150,000 miles. However my vehicle is not on the list for the extention. this issue is a safety hazard regardless of the vehicle type. I was lucky that no one was behind me or they would have hit me.

Filed Jun 3, 2025 · Electrical, Engine · FL

[XXX] once again while diving down the road 45mph Terrain once again goes in to park ,I was lucky the lady behind me wasn't to close .Also I contacted onstar when I was able to get vehicle moving at the store ..I told her what happen she ran diagnostics while parked at store said there was no codes I let onstar know this has happened several times..I had no warning, no indication, no lights came on.And I also let her know that this same vehicle was still stalling I was at intersection and the auto/stop is always on it will not let you bypass or default took it to dealership who I bought CPO back when it first would not let me turn it off cause its stalls at stop signs ,red lights etc crazy thing is if you turn the ac on it cranks up , if you hit the door unlock it starts... Thats not normal GMC knows that the dealership whom sold me CPO that wasn't the misleading is beyond crazy..GSM cussed me out It comes with life time warranty but when I had it towed right after I bought it 2 months ..I was talking about what the mechanics had said that this vehicle was in prior flood and accident GMC onstar has a different Vin then the one that on the vehicle..The doors are not original I can see the inside of steering wheel and on dash where they said air bags were deployed and they did a [XXX] job hiding it ... I paid over 32k for this 2020 Terrain that was advertised as CPO with 1 owner in Florida they showed me a fraudulent carfax, I pulled up my own and it came from New York ..This vehicle is not safe to drive but I dont have any other options..I have made complaint with both GMC and my finance company whom also wrote complaint on dealership and the told me I could rewind the loan but when I told dealership I knew that they sold me a vehicle that was not CPO and what I learned He came at me at dealership infront of workers and customers .. The vehicle just going to end up getting myself killed or someone else.. Semi had to run off road to avoid hitting me INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT