general problems of the 2020 GMC Terrain - part 1

On June 7, 2026, I was driving my 2020 GMC Terrain. I was going at about 40mph along a very busy main road. While slowing for a red light the check engine light turned on and the car displayed a notice about reduced engine power. Seconds later, the brake pedal became stuck and would not press down all the way and I lost braking ability. The car rattled/shook violently, made a grinding noise, and then the engine shut off and the car stopped abruptly, narrowly avoiding hitting the car in front of us. I turned on the hazard lights. I was not able to get the car to start again, nor was I able to get the car to shift into any other gear including neutral. We were nearly hit by other vehicles multiple times while attempting to get the car to move again, and to get myself and my child safely out of the road. Myself and multiple bystanders attempted to engage the transmission interlock override multiple time. We were eventually able to engage it and push the car to the side of the road. This failure created an extremely unsafe situation for all involved as this road is very busy and there were numerous near-collisions both with my disabled vehicle, and with other drivers serving out of the way and into other lanes at the last second. As time went on and the battery drained, most of the car's exterior lights turned off and other drivers had a hard time seeing my car. I used a strobe flashlight to alert other drivers but this required that I had to stand in the road near the vehicle. Police were called immediately when I found that we could not move the car out of the road, but they did not arrive. Ultimately the vehicle was stuck and inoperable in a travel lane for over two hours. The car was then towed to a nearby repair shop. The mechanic evaluation stated that the brake vacuum pump had failed resulting in loss of braking ability and expensive damage to the engine and other components. The manufacturer is aware of this issue. See: thieme, et al. V. General motors llc.

During my daily commute to work on the interstate the service break assist message came on my dash and when attempting to break the pedal was very hard, to the point where I had to push extremely hard and quickly realized I had to brake much much soon than normal to prevent hitting other vehicles. Sudden loss of brakes put me and other drivers at risk due to my near inability to slow down or stop and the sudden and unexpected nature of the event.

I am a [xxx] resident. While commuting to work in [xxx], my GMC Terrain experienced a sudden, catastrophic failure of the brake vacuum pump while traveling at highway speeds. When I attempted to slow down for the exit, the brake pedal instantly became extremely stiff and nearly impossible to depress. I realized I had suffered an absolute loss of power braking assist. To avoid a high-speed collision with heavy highway traffic, I was forced to deliberately steer onto the roadside rumble strips, relying on tire friction to slow the vehicle down. This severe near-miss left me terrified and distraught. Because the shoulder was narrow, my disabled vehicle was left partially protruding into the active roadway. Passing cars sped by so close that my vehicle was violently rocking, creating an incredibly unsafe situation. I was forced to call the state police for emergency assistance. They dispatched a trooper and a tow truck to remove me and the vehicle safely from the highway. The vehicle was towed to a mechanic in massachusetts. The mechanic discovered that the vacuum pump had internally exploded. This explosion sent catastrophic metal shards and debris directly into the engines oil galleys and oiling system. While the vehicle has 121,776 miles, this is not a normal wear-and-tear component failure. The brake vacuum pump suffered a catastrophic internal mechanical explosion at highway speeds, completely eliminating my ability to stop the vehicle. A mechanical component failure should never cause an immediate, life-threatening loss of brake control, regardless of mileage. This is a known, systemic engineering defect that is currently the subject of active federal class-action litigation (xxx v. General motors llc). This defect did not just cause an immediate life-threatening braking failure, it completely contaminated the oiling system, destroyed the entire engine, and rendered the vehicle a total loss requiring a full engine replacement. Information redacted pursuant to the freedom of information act (foia), 5 u. S. C. 552.

Transmission wouldnt shift. Sensor in car is causing issue, code is n 202321840.

I am submitting this complaint regarding a serious and dangerous brake failure involving my 2020 GMC Terrain slt with approximately 150,000 miles. While driving, the vehicle suddenly experienced a vacuum pump failure that caused a severe loss of braking ability with no warning beforehand. The brake pedal became extremely hard, and the vehicle would barely stop. This created a very dangerous situation and could have easily resulted in a serious accident. Thankfully, I was not driving at a high speed when the failure occurred, and there were no vehicles directly in front of me at the time. However, only minutes earlier I had been traveling approximately 65–70 mph on the highway. If this brake failure had occurred while driving at highway speeds or in heavy traffic, I truly believe it could have caused a major crash resulting in serious injury or death. What concerns me most is that there was no warning before the brakes failed. No warning lights and no issues with my brakes. The sudden loss of braking power was extremely frightening and created an immediate safety hazard. After researching this issue, I discovered that other GMC and gm vehicle owners have reported similar vacuum pump failures and brake assist problems. I believe this is a significant safety issue that should be investigated further. Drivers should not experience sudden brake failure without warning, especially on a vehicle that otherwise appeared to be operating normally beforehand. I am very thankful no one was injured in my situation, but I am concerned that another driver may not be as fortunate. My vehicle had to be towed to a nearby shop and they suspected it was the vacuum pump failure and the car started smoking badly. So I had it towed to the GMC dealership and they called me today to confirm that was the problem and it also caused damage to the camshaft. This is a known issue with the Terrain and there is currently a class action lawsuit.

After vehicle acting like it isnt getting power and trying to die, I pulled into a gas station and turned it off. When I went to restart it, the vehicle kept turning over and over automatically not wanting to start and the engine light came on. I let it sit for about 5 minutes and tried again. It did same thing. I tried a 3rd time pushing the gas pedal and it finally started. I made it home 2 miles away. Turned the car off and tried starting it again with same issues.

I was driving 55 miles an hour on an expressway. And suddenly my truck just shut off. The brake became very hard unable to break very scary situation for me and my children. Engine power was reduced and would not start, many errors came up. The vacuum pump failed, which also caused the cam shafts to fail. The vacuum pump exploded into pieces and sent metal into my engine.

Catastrophic engine failure; no warning lights,etc. Took place on or about end of January 2026. Car completely died and would not start. Car towed to dealer (GMC blaise alexander, hazleton, PA) vehicle inspected by dealer master mechanic and others. Engine completely disassembled. Unable to repair. No warnings, lamps, messages or other symptoms prior to failure. Tremendous expense had to be incurred by us over this incident. We had to purchase a new car. Terrain had been meticulously maintained by dealer since purchase. We still had over one year of payments remaining. Expected car to last closer to 200,000 miles. A new engine could have been installed, but cost was too expensive. We lost all of our equity in the vehicle.

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.

My a/c went out within 2 years of having the car in 22’. In 2025 I have had nothing but problems, the radio will go out when im driving for about 2 hours and it resets, the screen goes black, music stops, navigation stops and then it turns on like nothing happened. It happens everytime I drive 2+ hours. Back in September of 2025, I was on my way to work when I was stopped at a red light, it turned green and then my brakes locked up and I couldn’t drive my car had shut off, and wouldn’t come back on. I was stuck in the middle of the road not knowing what happened as the car had driven fine up until I stopped at the red light. Then tonight November 21,2025 around 0315 I was leaving work, I started my car, my car threw up a message that said “low fuel, 0 miles” I had half a tank of gas when I got to work. I turned my car off then back again and it did the same thing. I let my car sit for a second and then my gas gauge started to slowly increase to the correct amount of gas. Then when I got home (3 mile drive from work) I turned my car off and then back on and this time when I turned the car on my brakes were locked and I couldn’t start my car. All of the engine lights were on so I turned the car off and then let it sit for a minute before trying to start it. When I tried to start it this time, I couldn’t. It’s like the car had died and was getting no power. I couldn’t lock my car, no lights were working, I couldn’t turn it on or start it. Some time went by and my interior lights were on so then I started the car and it’s almost like my car reset. I can’t see my tires psi, the clock went to midnight (it was about 0330) it was all just very weird!!.

From a complete stop my car refused to accelerate no matter how much I pushed the gas pedal. I was pulling into traffic and was on a hill so my car rolled forward naturally into the road but would not respond to the gas pedal. The rpms didn't move, the car had power, I tried putting it in reverse and then back into drive. Nothing worked for a solid 2 minutes at least. Then all of a sudden it registered and worked. I was almost t-boned from a car coming through the curve but luckily, they were able to go around me in time. This put me and my small daughter at risk of being severely injured from a malfunction that I can't recreate to show the technicians. Since this incident, it has happened several times randomly. Sometimes I'm at a red light, or backing out of a parking spot, or pulling out into traffic. When it happens, there are no codes thrown to show any engine malfunctions, but it will not move! I've noticed more and more the lack of power when driving. Almost as if the transmission is slipping or losing power as well. I bought the car new, only have 38k miles on it, and service it every 5k miles at a GMC dealership. This is going to end up killing someone. The mechanic told me to trade it in, but I just paid it off and it's only 5 years old. There are multiple complaints about this same thing happening with tons of Terrains and there isn't a recall yet.

Driving down the road and an engine power reduced light came on and then the driver was not able to apply the breaks to stop the car. Almost ran into a car at a 4 way stop before getting the car to stop.

Driving down busy highway and suddenly had no brakes!!! no lights came on dashboard as a warning. Found out it was a braking pump that broke and shot metal pieces into the engine. Now im facing a new engine for a 2020 Terrain!!.

First problem was when the ac went out which affected the starter 2 weeks after that while I was driving something popped underneath the vehicle the vehicle completely stopped working when I checked underneath the vehicle there was leak ish a broken crankshaft car would not turn back on….

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.

As I was driving down the ohio turnpike on my way to work on Tuesday, August 5, 2025, my check engine light came on. Almost immediately I got a notification that the car was operating at reduced power. I had no previous issues with the vehicle. As I got off the turnpike my braking system failed. I was able to come to a stop partially in the grass before entering into oncoming traffic. The entire car shut down. I was unable to restart the car. We were also unable to put the car into neutral to push it off of the road the remainder of the way because the wheels were completely locked up at this point. The parking brake was engaged on its own. We also could not get the car into neutral. I had the car towed to a local repair shop, not knowing at all what the issue was. The vacuum pump had failed and broke apart in the engine. This caused my braking system to fail completely also. The vacuum pump on my 2020 GMC Terrain has been noted as faulty or defective. However, an official recall has not been issued for my vehicle. Had the pump failed a moment sooner I could have been in a crash trying to exit the turnpike. I took my vehicle to a repair shop and spent $1400 out-of-pocket. The car still does not run correctly now as there are pieces in the engine of my vehicle that were unable to be retrieved.

The contact owns a 2020 GMC Terrain. The contact stated while driving at an undisclosed speed, the vehicle lost motive power with the check engine warning light illuminated. The vehicle was towed to an independent mechanic, where it was diagnosed that the fuel pump control module had failed and needed to be replaced. The vehicle was not repaired. The dealer was contacted. The vehicle was not diagnosed or repaired. The manufacturer was not made aware of the failure and referred the contact to the NHTSA hotline for assistance. The approximate failure mileage was 88,000. The VIN was not available.

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.

While my wife was driving on [xxx] speed (60 –70 mph), the engine suddenly seized without warning. This created a dangerous situation, especially at that speed. Upon inspection, it was confirmed that a camshaft end cap detached, causing catastrophic internal engine damage. I believe this may be due to a manufacturing defect or insufficient part durability, and poses a serious safety risk to myself and other drivers. Please investigate this issue for broader safety concerns and potential recalls, especially if other owners report similar failures. Information redacted pursuant to the freedom of information act (foia), 5 u. S. C. 552(b)(6).

5. 25. 2025 - car shut down while at a busy intersection. Called amherst police due to location and how dangerous the intersection was. Family member needed to jump start the vehicle. Vehicle started before police arrived. Drove home. Called police to let them know we were no longer at the busy intersection. 5. 26. 2025 took out battery to check charge at auto store - tested good - 82%. Re-installed battery went to get gas thinking that may be the issue, low on gas, not the case the car wouldn't start at the gas station. Family member needed to jump start the vehicle again. Drove home, called dealer, taking to dealer next week 6. 4. 2025 due to availability of service. There were no warning lights prior to stalling out both times. This is very dangerous. We are afraid to drive this GMC 2020 Terrain.

The contact owns a 2020 GMC Terrain. The contact stated while driving 45 mph, the vehicle inadvertently lost motive power. The contact was able to pull over to the shoulder of the roadway, where the vehicle failed to restart. The check engine warning light was illuminated. The vehicle was towed to the dealer, who determined that the engine had seized. The contact was informed that the engine needed to be replaced. The vehicle was repaired, but the failure reoccurred. The vehicle was again towed to the dealer, who again diagnosed a failure with the engine. The vehicle was not repaired. After investigating the failure, the contact related the failure to NHTSA campaign number: 25v274000 (engine and engine cooling); but the VIN was not included. The manufacturer was notified of the failure, a case was opened, and the contact was referred to the NHTSA hotline for assistance. The failure mileage was unknown.

[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.

The contact owns a 2020 GMC Terrain. The contact stated that the vehicle failed to stop while driving 55 mph while depressing the brake pedal. The contact pressed the button that immediately shifted the transmission to park, and the vehicle came to a stop. The contact drove the vehicle to a safe parking space. After safely parking the vehicle off-road, the check engine and brake assist warning lights illuminated. The vehicle was towed to the dealer who diagnosed that the brake booster pump and camshaft had fractured and detached from the vehicle. The contact was informed that the brake booster, vacuum pump, and camshaft needed to be replaced. The vehicle was not repaired because the dealer was awaiting the parts to repair the vehicle. The manufacturer was not informed of the failure. The failure mileage was 101,700.

This message concerns a persistent engine light that activates and generates engine code p0299, indicating an engine underboost issue. There have been several occasions where I am driving over 55mph on the highway and my 2020 Terrain slt fails to pick up speed over 60mph in traffic. I took it to my GMC dealer earlier this year for them to diagnose, and they discovered that the charge air cooler tube had collected moisture. Once that was fixed, the vehicle was fine for about a month when the same thing happened. I took it to another GMC dealer and found that the turbocharger wastegate actuator had to be replaced. Once replaced, I had no problems until it began to get cold where I live. Now the vehicle is doing the same thing. Now what happens is the engine light will come on and give the engine underboost message but goes away after a week of driving. I have taken it to 2 dealers for diagnosis, only for the engine light to disappear before they can figure out what the problem is now. This continues to be an issue, as I frequently drive on the highway over 55mph for work, errands, etc. , and presents a potential hazard if I have to pick up speed and can't on a major highway.

The contact owns a 2020 GMC Terrain. The contact stated that the vehicle was taken to a dealer for an oil change. The contact stated that approximately 5 weeks after returning the oil change, while driving at approximately 65 mph, the vehicle and steering wheel started shaking abnormally and the vehicle lost motive power. The contact stated that the traction control, check engine, and stabili-trak control warning lights were illuminated. The vehicle was taken to a dealer where it was diagnosed that there was no oil in the engine and the spark plugs and ignition coils needed to be replaced. The vehicle was repaired; however, the failure reoccurred three weeks later. The manufacturer was not notified of the failure. The failure mileage was approximately 37,000.

GMC techs have already documented this issue could not be caused by wear and tear or lack of service - of which there is none the car has been serviced every10k miles as advised. GMC coperate has been contacted case # 71853883 the vacuum pump has failed due to mechanical failure causing it to explode and send pieces into the camshaft. The lack of vacuum caused complete brake failure rendering the car unsafe. GMC is aware of the issue as others habe reported it (I have proof of this) and refuses to recall the cars. The cars loose breaking in the middle of driving with no indicator lights or any other indications. The breaks had just been replaced in may - the incident occurred in October. Has not been driven since.

In September 2024 I was driving down the freeway and my car shuttered like the transmission was slipping. I then proceeded to get over into the right hand lane incase I needed to pull over thankfully, because then I lost use of my breaks, and then my ability to accelerate and steer. Then my car just shut off and would not stop. My vacuum pump just broke with no warning, it has been replaced and my car still won't start, it's going on 5 months now and they still can't figure out why.

Car was very well maintained 2020 GMC Terrain, no warnings prior to the issues. Car started shaking while driving, would not allow me to accelerate without chugging, multiple lights came on including flashing check engine light. Somehow the whole motor and engine needs replaced.

The contact owns a 2020 GMC Terrain. The contact stated that while his daughter was driving at an undisclosed speed, an unknown warning light displayed on the instrument panel. The vehicle started losing motive power and the vehicle shut off while in a parking lot. The contact was notified of the failure and a tow truck was contacted. While waiting for the tow truck to arrive, the contact's daughter was able to restart the vehicle and drive to the residence. The dealer was notified of the failure the following day and the vehicle was towed to the dealer. The contact stated that a diagnostic test was performed, and the contact was informed that metal shavings were found inside the engine and the vehicle was diagnosed with engine failure. The manufacturer was notified of the failure but offered no assistance. The contact was referred to the NHTSA hotline to report the failure. The vehicle was not repaired. The failure mileage was approximately 67,000.

The vehicle is a 2020 and should not already be having electrical issues. The vehicle repair is over 5k for needing a starter motor, water pump and drive belt. A starter should last up to 100k miles and water pump should last 10 years not 4. This vehicle is a lemon and should not have so many issues.

While driving I had to push the brake to the floor and a light came on saying reduced engine power. I pulled over right away and had my car towed to mechanic. The vacuum brake pump exposed and parts went into the engine. The mechanic got all the parts out but now engine has low compression and needs a new timing chain. This is over $3,000 so far. Gm recalled other vehicles with the exact same pump ? why not the Terrain.

While driving reduce engine power light came on and the brakes gave out. I weigh 250 lbs and took all my strength to get brakes to stop car. I tow it and mechanic showed me vacuum brake pump blew up and went into engine. He replaced that and timing chain but still needed work. Towed it to dealer and it needs a new engine $11 000. The dealer informed me they see this alot. ! why has gm recalled some on the vehicles that has this pump but not the Terrain. This is dangerous. If my daughter was driving she couldn't stop this car. It's now junk.

The vacuum pump locked up and sheered off the end of the cam shaft and made the cam skip timing and destroyed the motor. While driving no check engine likes till after I lost power. Luckly I was able to roll to a stop the pumps have been a problem the car is only 4yrs old and has 71000 miles.

Purchased vehicle brand new- beck & masten Buick gm - houston, TX 9/7/2020 performed rout maint regularly. Last oil change 1-5-2024 before catastrophic failure and complete engine seizure. Towed to wiesner GMC 1-14-2024 1-12-2024: mileage on car roughly 99k- had no issues no check engine light, no mechanical failure or indication that anything was running other than normal. No start on 1/12pm after work, tried to return next day with battery , changed out battery, engine still would not start, after new battery installed and we attempted to start, that is when engine started making loud shaking motion while attempting to start, windshield wipers came on randomly. First initial diagnostic: found all oils & fluids in check, could not identify cause of failure, would have to break down and take apart. Had to authorize the tear down at a 1800. 00 cost, 2/2/2024: broke down engine, found that the crankshaft would move one way , but not other, removed the engine from transmission and now crankshaft moves freely. Now the ac comp is locked up (excessive play on magnet & clutch) , tech still unable to identify what caused the failure, they advised that they found traces of metal in oil pan, scored cylinder walls, starter shorted as well. They still could not indicate where these metal pieces came from, how or that it was due to owner negligence or manuf defects. Again this is a vehicle with 99k miles and now we were looking at a 15k price tag for a new engine, turbo, ac, starter on a car that is worth 12k. This is absolutely insane. We reached out for goodwill discounts for some assistance since the dealership could not solidify a cause of failure, but gm decided to not warranty and stand behind their product. We were left with a rebuild option for 7500. 00. Which we had to do in order to get the car back. I am completely disappointed in gm as a company. This engine should have never failed at 99k.

2020 GMC Terrain engine stopped working. Put in new engine. After one week new engine blown. We were 2000 miles away on vacation. I need a free rental I was with no car for a month and after only one week again for 3 weeks. Compensation request: lost wages hospital visit extra hotel nights gas food car and insurance payment.