Power Train Problems of GMC Terrain - part 1

VIN: [xxx] mileage: approximately 103,576 incident location: [xxx] safety complaint: while my wife was driving our 2019 GMC Terrain into a shopping center parking lot, the vehicle suddenly experienced a severe loss of braking assistance. The brake pedal became extremely stiff and difficult to depress, and she was barely able to slow the vehicle. This occurred unexpectedly while the engine continued running, creating a serious risk of a collision. Following the incident, I inspected the vehicle using an obd-ii diagnostic scanner, which identified diagnostic trouble code p0016 (crankshaft/camshaft position correlation). The vehicle also displayed an oil-pressure warning. We subsequently had the vehicle inspected by john's automotive care in [xxx] on xxx. During the inspection, the technician discovered a significant amount of metallic debris in the engine oil. The repair facility suspects a mechanical failure of the engine-driven brake vacuum pump, potentially resulting in damage to the engine and lubrication system. The repair facility recommended replacing the mechanical vacuum pump and engine oil-pressure switch and performing an oil change. However, the service representative explained that these repairs would not guarantee the engine's continued reliability because the engine was compromised and could fail at any time. We are extremely concerned that a failure involving the brake vacuum pump could cause sudden loss of braking assistance without adequate warning, potentially resulting in a serious accident. We request that NHTSA investigate whether this failure represents a safety-related defect affecting the 2019 GMC Terrain and other vehicles equipped with similar engine-driven brake vacuum pump systems. Information redacted pursuant to the freedom of information act (foia), 5 u. S. C. 552(b)(6).

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GMC adaptive learning transmission problems that lead to safety concerns, emissions reduction in mpg, and increased wear of the transmission. Regarding gm’s 9t45 automatic 9 speed transmission. Problem: - the gm adaptive learning of the transmission does not have safe guards in place to prevent unsafe sift patterns and behavior. This results in shift flair behavior where the transmission will drop out of 3rd gear and pause before shifting to 4th gear. It will learn to lock out 9th gear and it will max out with 8th gear at freeway speeds reducing mpg. And it will fail to downshift appropriately while driving leading to the operator wondering why the vehicle will not accelerate when needed; this casual downshift delay then results in excessive downshifting to the lowest possible gear where the vehicle will then lurch forwards; and then it will pause and maintain said lower gear and continue accelerating for 1-2 seconds while the operator presses the brake pedal in response of the vehicle jumping forwards. Individual situations: 1) lack of 9th gear use at freeway speeds. This is reducing the advertised emissions based on epa testing. This behavior skews official epa test results because vehicle operation is not as advertised. 2) shift flair and unsafe shift delays. This is the most serious behavior. It leads to pauses and delays in acceleration of up to 5 seconds, and it leads to pauses and delays where the vehicle continues to accelerate up to 3 seconds after letting off the accelerator and pressing the brake. 3) excessive wear. The badly learned behavior is causing issues with shift control pressure and logic, excessive clutch wear leading to damage and worn clutch packs. Analysis: - resetting the gm transmission adaptive learning to factory removes these problems, the trans will relearn bad behavior within 2-3 weeks of daily driving. Reset was performed using an autel hot function “quick learn” procedure for the transmission.

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My 2023 GMC Terrain has experienced two separate incidents of complete loss of motive power/engine propulsion while being driven. The vehicle suddenly loses the ability to accelerate and maintain normal propulsion, creating a serious safety risk in traffic. The first occurrence was on August 8, 2026. The vehicle was subsequently diagnosed and repaired by an authorized Chevrolet dealership with general motors involvement. After those repairs were completed and the vehicle was returned to me, the same loss-of-propulsion symptom occurred again on September 26, 2026, approximately two weeks after the vehicle was returned. The second failure occurred while I was actively driving and again resulted in the vehicle being unable to maintain normal propulsion. The vehicle required towing and is currently at an authorized GMC dealership for diagnosis. The vehicle is available for inspection. This recurring failure creates a risk to the driver, passengers, and other motorists because propulsion can suddenly be lost while the vehicle is operating on a roadway.

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The contact owns a 2019 GMC Terrain. The contact stated that after pulling into a parking lot, the vehicle failed to shift into park. The vehicle was towed to a dealer where the contact was informed that three fault codes were found. The dealer informed the contact that the transmission needed to be disassembled for a full diagnostic test. The vehicle was not repaired. The vehicle was scheduled for the transmission to be disassembled for the diagnostic test. The failure mileage was approximately 60,000.

Avis rental. Vehicle simply shut down while driving and would not re-start. Vehicle could not be put into neutral to move from roadway. Emergency services vehicles had to remain on site awaiting tow vehicle. Very dangerous situation.

Factory powertrain programming actively locks out 9th gear (overdrive) during freeway driving at speeds exceeding 60–65 mph. The vehicle refuses to upshift from 8th to 9th gear, forcing sustained high-rpm operation during standard highway cruising.

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.

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The car suffered a long crank, then stalled completely while moving on a public road, which is a severe safety hazard.

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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?.

No engine lights are on. When at stops it starts chugging and when I accelerate sometimes it does not go like it should. It idles high and feels like it is slipping. I have almost been hit in the rear several times when this happens. One lady did rear end me but the damage was so little that I did not call the cops. This vehicle has not been inspected and it is available for inspection at any time.

Leaking transmission fluid at 7,000 miles. Technicians noticed during routine oil change at dealership.

Accelerator lag from any speed or stop. The care will take several seconds to hunt for the correct gear before shifting to accelerate. Or it will delay acceleration for several seconds while your pressing the accelerator. No ses indicator active. Mechanics can’t find issues. Other owners on forum a report the same sluggish behavior. These 1. 5 turbo cars seem to need a software fix that they are not receiving. It’s like the drive by wire doesn’t register. Affects any gm vehicle with the 1. 5 turbo and 9 spd auto.

The contact owns a 2023 GMC Terrain. The contact stated that while driving at various speeds, the vehicle unexpectedly decelerated and failed to properly accelerate. The service transmission and service fuel management system messages were displayed, and the check engine warning light was flashing with several other unknown warnings illuminated. The vehicle was taken to the local dealer and while test-driving the vehicle, the vehicle stalled. The vehicle was towed back to the dealer. The cause of the failure was not yet determined. The manufacturer was notified of the failure, and an engineer was sent to the dealer to inspect the vehicle. No further information was available. The contact stated that the transmission module was previously replaced, but the failure persisted. The failure mileage was 27,000.

My 2016 GMC Terrain 2. 4l ecotec first stalled while idling at a red light in raleigh, nc. I restarted it and it sounded different, so I drove it home. The next morning it would not start. The failure occurred at approximately 69,939 miles with no meaningful warning. The dealer’s diagnostic report states there were no current relevant codes and no relevant codes in history. The dealer documented major timing-system failure: timing chain tensioner failure, timing chain guide failure, a timing chain guide bolt pulled out of the cylinder head, aluminum contamination in the cylinder head/oiling system, and engine replacement recommended. The vehicle was found unsafe to operate. This vehicle regularly transported my family, including my children. If the stall/no-start failure had occurred at highway speed, while merging, or in heavier traffic, it could have created a serious crash risk. The oil was maintained outside the dealership network and had been serviced before failure. I also topped off the oil shortly before this occurred. The 2. 4l ecotec engine family is known for oil-consumption issues, yet this vehicle gave me no direct warning that oil consumption had reached a dangerous level. A reasonable owner would not know to check oil every day when there were no relevant stored warning codes. Other NHTSA complaints involving 2016 GMC Terrain vehicles describe similar patterns: oil consumption, no warning lights, sudden stalling or no-start conditions, timing-chain failure, and engine replacement recommendations. I am filing because this appears to be an ongoing safety risk involving oil consumption without adequate warning, timing-chain/timing-guide failure, internal contamination, and sudden engine failure. I request NHTSA review this issue for investigation or recall expansion before this failure mode causes a preventable serious crash, injury, or fatality. The vehicle was inspected by a GMC dealer and remains unrepaired.

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Automatic transmission solenoid control valve body got stuck open and ruined the whole transmission. This has been a reoccurring problem with these vehicles. Image is from a code read. Issue was confirmed by gastorf Chevrolet, and an independent transmission shop.

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The contact owns a 2022 GMC Terrain. The contact stated that while driving 45 mph, the vehicle began to shake independently. No warning light illuminated. The vehicle was taken to the dealer where it was diagnosed that the front drive axel needed to be replaced. The contact was relating the failure to technical service bulletin: 20-na-227 (wobble or vibration during hard acceleration); however, the VIN was not included in the bulletin. The manufacturer was notified of the failure, and they informed the contact there was no recall for the failure. The failure mileage was 64,000.

Took dealer 3/26 for sam issue engine power reduced after already cause me hit curb. Got it out 4/1/26 now 4/5/26 it happened again same codes after they claimed they fixed it. Also keep having emergency services come on a caused my dashboard out. My issues is car keeps stalling losing power. Same codes as week ago after dealer fix. Also 4 time took for noises in my car from passenger side. They keep telling me they can’t replicate it, but you can clearly see where the door is not lined up. This has been going on for over 30,000 miles for that. Like some of these issues have been going on since the 36,000 but now I’m having issues where I’m losing power like this is insane all before 60,000 miles which I’m about to hit. It’s gonna end up getting me killed on the interstate.

While driving the vehicle, the engine light came on, plus message board said service transmission and the engine went into limp mode. We let the car sit for awhile and checked the car. A scan said it was the pressure solenoid a in the transmission. The car sat for a day and the light was off. Drove the car and then it acted up again and now reverse doesn't work.

Out of nowhere and driving this morning, my engine reduced power came on. Then I started losing power in the car then it died on me once out of nowhere. I managed to make it home an hour and a half later, but that could’ve got me killed stopped by autozone since dealerships closed today and it tells me that it’s code p228c, p0089 fuel pump. And then last night my emergency service calling came on which one I looked it up so something to do with onstar and could be a module so I’m not sure what that is. And then you add on the fact all the sudden in the last 24 hours, my screen keeps going in and out are not working last week. My volume wasn’t working. I love this car, but it seems to have a lot of issues all of a sudden and I’m fixing to be at 60,000 miles which is a big problem considering warranty will be expired. I’ve already had issues with squeaking and squealing from the windows that they claim they can’t find nothing and I’ve had to listen to it for almost 60,000 miles. I had to get this car because my other car blew up on me and I can’t afford another new car. I’ll be taking it to the dealership first thing in the morning and I hope to god that something can be fixed cause we’re in one car family.

The vehicle has experienced a recurring transmission-related defect that has required multiple repair attempts by an authorized GMC dealership. The transmission system has also exhibited fluid leakage. Despite prior repairs, the problem has continued to reoccur. Transmission and associated transmission fluid sealing components. The vehicle is currently available for inspection upon request. A transmission is a critical safety component that transfers engine power to the wheels. A transmission defect or fluid leak can result in loss of propulsion, hesitation, inability to accelerate as expected, unexpected changes in vehicle operation, or transmission failure while driving. These conditions could increase the risk of a crash, particularly when merging into traffic, crossing intersections, or traveling at highway speeds. Transmission fluid leaking onto roadways or vehicle components may also create additional safety concerns. The vehicle has been presented to an authorized GMC dealership for diagnosis and repair on multiple occasions. The dealership has acknowledged and attempted repairs related to the transmission. The vehicle has been inspected and repaired by authorized GMC service personnel. No police involvement. No independent inspection has been performed at this time. Manufacturer-authorized dealerships have documented the repairs. Symptoms included transmission-related concerns and transmission fluid leakage. The defect first appeared while the vehicle was under warranty and has continued despite repair attempts. The recurring nature of the transmission defect and fluid leak has reduced confidence in the vehicle’s ability to operate safely and reliably. The vehicle remains under warranty and has undergone multiple repair attempts without a permanent resolution.

The contact owns a 2026 GMC Terrain. The contact stated that while attempting to depress the accelerator pedal after coming from a complete stop, the vehicle started wobbling. A dealer was contacted. The vehicle was taken to the dealer to be diagnosed; however, the diagnostic result was unknown. The vehicle was not repaired. The contact associated the failure with technical service bulletin: pit6466 (shimmy, shake or wobble when leaving a stop); however, the VIN was not included in the bulletin. The manufacturer was notified of the failure and informed the contact that there was no recall for the failure, and opened a case. The failure mileage was 5,200.

The contact owns a 2019 GMC Terrain. The contact stated while driving at an undisclosed speed, the transmission unexpectedly shifted into neutral(n). There was transmission fluid on the ground, and the vehicle became disabled. The vehicle was towed to the dealer, where it was diagnosed with a transmission accumulator leak. The vehicle was not repaired. The manufacturer was not notified of the failure. The approximate failure mileage was 180,400.

The contact owns a 2023 GMC Terrain. The contact was informed by his wife that while attempting to accelerate from being stationary, the vehicle was shaking abnormally and hesitated before accelerating. There were no warning lights illuminated. The vehicle was taken to the dealer to be diagnosed but the cause of failure was not yet determined. The vehicle was not repaired. The manufacturer was informed of the failure. The manufacturer opened a case for the failure. The failure mileage was approximately 13,000.

The turbo went completely out at around 105k miles while I was driving to work. I had to coast into a repair shop because it was smoking and wouldn’t go over 20mph and then have it towed to the place that repaired it. Since then, the transmission is having trouble shifting gears. The car struggles to accelerate and I have to go abnormally slow after coming to a complete stop in order for the car to get into gear. The onstar diagnostic says everything is fine but it is clearly not fine.

I bought my car in July of 2025 and since then my car keeps derating and reducing engine power while driving down the road at 70 miles an hour. It cuts out and decreases power. I took my car to the shop twice to have them tell it needed an update. I drove away and then the car does it again. Since December my car has down this decreased power, derated notice more than 30 times!! it is a safety risk for me and my family because you never know when it will happen on the interstate and when you will lose power. I have almost been rearended 3 times due to this issue and no one can seem to fix the issue.

The contact owns a 2018 GMC Terrain. While attempting to shift to reverse(r) out of a parking spot, the message “transmission unable to shift” was displayed on the instrument panel, and the transmission was unable to shift into reverse(r). The contact called for tow truck assistance. The vehicle was unable to shift into neutral (n). The contact stated that prior to the transmission failure, the “service transmission soon” message was displayed. The vehicle was towed to a local dealer to be diagnosed, and it was determined that the transmission had failed and needed to be replaced. The vehicle was not repaired. The manufacturer was not informed of the failure. The failure mileage was approximately 245,000.

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I was driving the car on 12-22-25 I lost power my car died on i94. Battery died the dearlship couldnt get the code. Got the car back on 12-26-25. Engine light came on carrie GMC replaced battery . Car back on 12-29-25. . Engine light back on 12-31-25 car back on 1-8-26 replacled catalytic conveerted and oxy sensor. 2-20-26 driving on 1-94 lost engine power car back on 2-25 feul pump and feul line. Drove 300 miles engine light back on. Back to currie GMC on 2-26-26 untill 3-2-26 replacred heated oxygen sensor . 3-6-26 replaced catelytic converter and oxyger sensor for the second time.

This vehicle was bought new and is a new 2026 GMC Terrain denali with less than 5,000 miles at this time. It is a continuous event and not a specific failure date, but began soon after purchasing. The specific parts are unknown. It could be tires, wheels, steering parts (cv joints, control arms etc) or possibly transmission. I took it initially to the purchasing dealership and they took it for a ride and just dismissed the problem without investigating. Several days later I called and talked to the person who sold me the SUV and was told either him or service manager or both would call me, but neither did so. They were to set up a return date. After this insulting experience I decided to take it to a Cadillac dealer that I have had great experience with in the past. They took it for a ride and did experience the problem and investigated what they thought could be causing the SUV to wobble, shimmy, or shaking sensation. This Cadillac dealer said there investigation showed nothing wrong and returned the vehicle to me and said nothing could be done unless gm gave them permission. Next I wrote to the service manager expressing my disappointment in nothing being done and my disappointment in general motors. There is a service bulletin (document pit6466). This makes four efforts on my part to get satisfaction with this 2026 GMC Terrain denali and how it is not fun to drive and there is anxiety on the safety of the vehicle when being driven. For the problem I am experiencing with this 2026 GMC Terrain denali. There is the sensation of a “wobble, shimmy, or shaking” under low to moderate acceleration when going straight or turning. It could be tires, wheels, steering parts or power train. It is difficult to tell. Sometimes the sensation is as if the wheels will fall off. This is an awful feeling and gives you the feeling the SUV is not safe and it is not fun to drive at all. * why do I have to drive a brand new expensive SUV and feel unsafe and not enjoy do so?.

Suvs check engine light turned on and went into reduced power mode, it has been very cold for approximately a month. Code p0299.

Vehicle did not go into park when the ignition was turned off. Car started to roll while passenger was getting out of the vehicle as another vehicle was parking beside us. The other vehicle could not avoid our rolling vehicle. Passenger had to quickly sit down to avoid being hit. The next day the vehicle was taken to the dealership, and they could not find anything wrong. They gave us a copy of bulletin#08-07-30-026i. We were not aware of any problems or bulletins being issued prior to the accident. We had repairs of $2,705. 71 and don't know what the other driver incurred.

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The contact owns a 2026 GMC Terrain. While driving at 28 mph, the rpm became elevated to over 3,000 rpm. There was no warning light illuminated. The contact immediately pulled over and then resumed normal operation after the failure. The vehicle was taken to the dealer to be diagnosed; however, no cause for the failure was found. The contact was advised to bring the vehicle back to the dealer if the failure reoccurred. Approximately one week after the initial failure, while driving approximately 30 mph, the transmission unexpectedly downshifted to l2. There was no warning light illuminated. The contact pulled over and restarted the vehicle, and the vehicle was taken back to the dealer. A diagnostic test was performed, and the contact was informed that the transmission needed to be rebuilt. The manufacturer was notified of the failure and was provided a case number. The vehicle remained with the dealer unrepaired. The failure mileage was approximately 1,300.

Powertrain system failure while driving, causing complete loss of power on road. The car lacks any accessible manual overrides to put in neutral or turn off parking break. This leaves the car stuck in park with all four wheels locked in the middle of the road in an incident with no safe way to move or tow the vehicle. When attempting to tow car must be dragged, and parking brake continuously engages. Tow attempt took nearly 3 hours to saddle the vehicle in the roadway. Vehicle currently awaiting formal inspection/repair from dealership.

Vehicle was started for the second time that day on 1/5/26 and the engine light was on. I drove the vehicle to an auto parts store to have them check it with an obd-ii scanner. It had code p050f. I had no idea how serious this issue could be at the time. I made an appt with the GMC dealership and dropped it off the evening of 1/6/26. They said there was a software anomaly in the engine control module and needed to be reprogrammed. I paid the $200 diagnostic fee for them to reprogram it. I learned that this anomaly could have caused my brakes to not work while driving it. I had been driving the vehicle back and forth to work until I dropped it off. This issue could have caused serious harm or death to myself and others. While researching online, I've seen that other vehicles have had safety recalls and additional warranties added for these issues, but my vehicle isn't included in this.

I am filing this complaint to report a catastrophic engine failure involving my 2017 GMC Terrain equipped with the 2. 4l ecotec engine, which I believe is the result of a known manufacturing defect related to excessive oil consumption and premature internal engine wear. At approximately 88,000 miles, my vehicle experienced severe engine failure, including excessive oil consumption, timing chain failure, and complete engine failure, which has been confirmed in writing by a licensed repair facility. The shop determined that the engine failure was caused by oil starvation resulting from excessive oil consumption, leading to internal engine damage and timing chain failure. This failure occurred without warning and rendered the vehicle unsafe to operate. Sudden engine failure creates a serious safety risk, including loss of power while driving, inability to accelerate, and increased risk of collision. This engine failure matches a well-documented defect pattern involving general motors’ 2. 4l ecotec engines, which have been the subject of class-action lawsuits, settlements, and jury verdicts related to premature piston ring wear, excessive oil consumption, and resulting engine damage or failure. These issues have been widely reported in Chevrolet equinox and GMC Terrain vehicles within my model year range. My vehicle was properly maintained, and this failure was not the result of neglect, misuse, or normal wear and tear, but rather a latent manufacturing defect that manifested after the warranty period but well within the reasonable life expectancy of the engine. I am requesting that NHTSA formally document and investigate this defect, as it presents a significant safety concern for drivers operating vehicles equipped with this engine. I also request that general motors be required to address this defect to prevent additional engine failures and potential safety incidents.

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Drove car approximately 15 miles. Parked car. Car would not turn off. Message- transmission/park. Wouldn't car stayed neutral. Had to call wecker to take dealership. . . . Diagnostic solenoid valve body faulty. . . . 2019 Terrain miles 91669. Is there recall. Have more reports of issue. Should this happen with a well maintained vehicle all maintenance updated to date.