2020 GMC TERRAIN Service Brakes Problems

While driving down the interstate a notice popped up on my dash about the brake assist. When I attempted to slow down the vehicle to safely pull over the brake pedal was very hard to push. I was able to slow the vehicle to a complete stop but needing to use both feed and press hard with all my weight. Once the vehicle was parked and shut off I turned it back on to have the check engine light pop up on the dash. I contacted Onstar and was towed to a dealership. The brake vacuum pump had broken off at the cam shaft and required extensive repairs. It is my understanding that this is a common occurance and there were previous recalls on the other style Terrains due to the same issue. yet they used the same part on the newer body style being fully aware of the design flaw.

Since August 2024, my brake booster has gone a total of five times each time with the notification on the dash service brake assist. And it just went again as of two days ago. I’ve brought it to Firestone where they have replaced it each time with a warranty on the part. I called them yesterday to tell them that it went again and they refused to fix it telling me that they got the part from the dealership and that I would have to take it there so the dealership would have to figure out what’s wrong with it as to why the car is “chewing up” the part. I have young kids and this part has gone five times.

While driving my brakes failed. I was unable to stop my car, my brake pedal became very stiff and I could not stop my car. There were no warning signs or lights on indicating there were any issues with my car prior to this happening. I had to have my car towed to the dealer. The current estimate is for a vacuum pump failure resulting in camshaft damage. Both need to be replaced. I see other GMC cars were recalled for what appears to be a similar issue. I am lucky no one was injured as this could have very easily resulted in a fatal event. I have never heard of such a thing happening before and am beyond belief that this has occurred. This is the third repair I've had done this year. I have also replaced a booter pipe and valve gasket due to leaking oil. The amount of repairs required in such a short a time seems excessive.

While driving on a main road at around 45mph the vacuum pump that supplies brake fluid to the brakes failed. The car was unable to be stopped and had it not been late in the night I could have crashed into other vehicles on the road or hit someone walking. There was not indication prior to the malfunction and was very sudden. This issue has been observed by the dealer as well as multiple other individuals with the same problem for this make and model of car as well as others by the same manufacturer for similar years of manufacturing. This part has also been shown to break into the engine causing complete engine failure due to lack of a shear pin on the vacuum pump.

Vacuum pump went out. It was a recall, previously on older models, but this model needs to

I filed a complaint with NHTSA on November 3, 2025, about my brake system. Here is another one adding more information. I had to have another brake system part replaced. This time it was the brake booster. Cost $1441.63 (covered by extended warranty actual cost to me $100.00.) So far, I have had the booster sensor replaced twice, the vacuum pump and now the brake booster. I asked the mechanic how many parts related to this system were left to replace? This vehicle has 66,000 miles on parts for the braking system started needed to be replaced at 37,000 miles. The total cost for parts, labor is about $500. That does not include the loss of use for this vehicle which is about 15 days. Taking days off of work about 6 days. This has been a problem for GMC Terrains since 2015; there is still a problem with 2020 model year. Please do something before there is a loss of life due to brake failure.

Check engine light is on took vehicle to dealership 10/13/2023 vacuum booster sensor replaced (37,435 miles) $0 GM Covered cost 12/9/2024 brake vacuum pump replaced (56,456 miles) $0 extended warranty 1/8/2025 vacuum booster sensor replaced (57,087 miles) $252.48 not covered by warranty Check engine light is on 10/11/2025 took to dealership. They were unable to find issue light was off, was told that GM had recommended several things that could be the cause of light coming on still could not find issue. Last thing GM and dealership recommended was to replace the battery. Cost $104.00 Check engine light came on 10/25/2025 while returning home from Tennessee to Michigan, light came on in Louisville, KY. Had it scanned, booster sensor was the cause. Called AAA had them replace battery light went off. (as you know that if you do that it reset the computer not surprised light went off drove rest of the way home to Michigan) Cost of replacement battery $295.00 Check engine light came on again 11/2/2025 my best bet is that it is booster sensor again. NHTSA and GM need to fix this issue. I have not lost breaking ability yet but the horror story that I've read on this site scars me. WHAT ARE IS NHTSA AND GM GOING TO DO WAIT UNTIL SOMEONE IS KILLED BECAUSE OF THIS ISSUE !!!!!!!!

SERVICE BRAKE ASSIST CAME ON, CHECK ENGINE LIGHT CAME ON AND VEHICLE WAS HARD TO STOP. Took to authorized service dealer and all parts were replaced. After driving it for a little while, SERVICE BRAKE ASSIST BACK ON, CHECK ENGINE LIGHT BACK ON AND VEHILCE IS HARD TO STOP.

Break assist light comes on and brakes stiffen suddenly with no warning. Happened 6 times now in a 3 year span. Gotten it "fixed" each time but it keeps happening

On my 2020 GMC terrain the vacuum pump failed and caused my braking system to go out completely. I had to almost stand up on the brakes to get the car to stop and thankfully I got it come to a stop before smashing into another car. I contacted gmc and while they know this is a ongoing problem and there is a warranty out for this particular problem (150,000 miles or 10 year warranty) I was told it is part/ factory specific and that if it was manufactured in certain facilities or had certain parts that they would cover the cost to fix it but however my vehicle was not covered. This poses a dangerous problem for GMC owners. As soon as the check engine light came on I had absolutely no control over the brakes and it was a miracle it stopped. There was no warning prior to this incident and upon looking up information this seems to be a recurrent problem that GMC needs to address seeing as they say they value their customers.

My 2020 GMC Terrain brakes pump failed causing me to hit the median wall on the highway.

While driving my 2020 GMC Terrain (VIN: [XXX] ) with approximately 110,501 miles, I experienced a sudden and complete loss of brake assist. After about 2 hours of highway driving, I exited and the brake pedal became extremely hard to press, making it very difficult to stop. No warning lights or messages appeared before the failure. The dealer diagnosed the cause as the brake booster vacuum pipe exploding internally, which immediately eliminated vacuum to the booster. This created a serious safety hazard and nearly caused a crash. I have since had the part replaced, but the fact that this component can fail without warning at highway speed is alarming. GM has issued TSB 21-NA-107 describing this exact failure mode, which indicates it is a known issue. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

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!!

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.

I was driving on the expressway, attempted to brake and the brakes were stiff and would not go down to stop the vehicle. . Thankfully, I was able to glide over three lanes of traffic and exit the expressway and glide into a parking lot and drove around until the car came to a stop. No lights. No warning. The car had to be towed to my mechanic. This could have been catastrophic. I could have killed someone else or myself. This is the second time that this has happened with this vehicle!!! By the grace of God I am still here writing this complaint. I am traumatized and do not feel safe driving this car. They MUST RECALL this vehicle before somebody gets killed. The issue is with the vacuum pump and I have seen other complaints about the same issue.

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.

I was driving on the highway & my brakes failed. My brake pedal was completely hard & could not be used. i had to steer onto an exit ramp & be towed to the dealership. There was absolutely no warning of this happening. Once at the dealership, they confirmed it was my vacuum pump that blew up, which damaged the camshaft & caused pieces of metal to be floating around in my engine. The greater portion of the repair was covered under warranty, however, I had to pay $350 out of pocket. This could have been catastrophic. I or others on the road could have been injure for worse. This system failure should be fixed immediately and owners be compensated. I do not feel safe driving myself or my family in this vehicle after experiencing this occurrence.

I got off a highway exit ramp and with no warning my brakes were hard to press. There was no warning lights on my dash. The brakes take a lot of force to push for a stop. The warning light finally came on a day later with codes p0556 and u040171.

On Monday 5/26/2025 I was on the way home from work, coming down my street to turn in my drive (at approximately 2130) I pushed on the brake getting ready to make my turn, my car would not stop. It traveled maybe 100 -200 feet before coming to a stop. The brake pedal would not push in. (As I live on a cul-de-sac, if this happened during the daylight, there would have been children playing in the street and I could have killed someone's child). I managed very slowly to reverse the car and finally get it in the driveway. I thought it was going to hit my house!! Upon reading a lot of issues and complaints on my vehicle make/model I pretty much figured it was the brake vacuum pump. I called GM, however my car has 74,000 miles, is out of warranty and no recalls for my VIN so I'm told I have to have it fixed. My neighbor is a certified mechanic and has a shop. He looked at it and confirmed it is the vac pump. Not only that but the end that goes into the motor has sheared off and not there is metal pieces and fragments in my motor. I had to have it towed to his shop. (this morning) As of right now I am waiting to see if the motor can be flushed or if I am going to end up having to replace motor. I have missed several days of work due to transportation and now have to rent a car, and pay who knows how much for repairs which could easily cost thousands. I live week to week and still make payments on this car!! This is a faulty part and should have been a recall as I have read on many many complaints of bad brake vacuum pump on the GMC Terrains even the 2020 models and up. Some of the others are already recalled but not mine. In the photos, on one you can see the big chunk of metal. On another where the piece came of of motor you can see where metal was scraping the camshaft in the motor and very small metal fragments around the opening

My 2020 GMC Terrain (under 100K miles) was running great until one day, after starting the vehicle, I shifted into reverse and felt soft brakes before the engine suddenly shut off. A licensed mechanic diagnosed the issue, pointing to Technical Service Bulletin #PIP5835, which identifies a defective brake vacuum pump. This failure caused damage to the exhaust camshaft and timing belt, ultimately leading to the recommendation of a full engine replacement. GMC’s response? They advised me to pay for their diagnostics and repairs, then file for a "Goodwill Repair," which they admitted was unlikely to be approved. Meanwhile, GM has since replaced this defective vacuum pump with an electric version, acknowledging the flaw—yet leaving owners like me to cover the cost. I believe GM should stand behind their product and take responsibility for this engineering failure, instead of forcing customers to absorb the expense.

Brakes stopped working while driving. Yes it has been reproduced by mechanic. No it has not been inspected by manufacturer. “Service Brake Assist” message populated after failure.

my vacuum pump went out. my brakes went out at 86k miles. very pour design.

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.

No warning, the brake pedal went stiff as a board. No brakes could not stop doing 35 on a residential road. Had to coast to a stop in neutral.

The brake system failed. No warning. When the brakes failed, driver ran the car into a tree to stop instead of hitting pedestrians or other vehicles

My Terrain has a light that has been coming on for a couple months. Service Brake Assist. I took it to the dealer after my brakes locked up and about $800 after getting it fixed the light continues to come on. The forward collision light comes on every time I start the car. More the check engine light came on and says engine electrical system. What the heck is going on? I love this car and take very good care of it but I feel like the $800 that I just spent was a waste. I fear that I will get in a wreck like when the brakes totally locked up and I couldn't press on them.

Slowed down from coming off of the highway to turn into the gas station and couldn't slow down. The brakes FAILED. Was trying to pump them and was able to come to a forecful stop, nearly colliding with the car in front of me and then again at the gas pump. Car had a failed vacuum pump at 65,000 miles. If this happened during normal rush our, my kids and I would have been sandwiched between two cars. Fatal flaw that clearly GMC already knows about. The Terrain should be included in the recall.

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.

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.

Incident happened August 9, 2020. Brakes suddenly stiffened and unable to stop vehicle. There were no warning signs or indicators. Thank goodness I was going at a lower speed and was able to coast into an area to stop. Ended up being the vacuum pump. This needs to be recalled ASAP. This could have been a fatal accident. I have kept the old vacuum pump as well as the pieces that were thrown from it that the mechanic had to dig out.

As I was driving, brakes became very hard to press. I was barely able to slow down to bring the car to a complete stop. Brakes became very stiff and required a ton of force to come to a complete stop. This came with no warning signs or alerts from vehicle. It was only after this occurred that the Service Break Assist light came on.

The contact owns a 2020 GMC Terrain. The contact stated that while driving 50 MPH, the vehicle lost braking power. The driver was able to pull over safely. There were no warning lights illuminated. The vehicle was towed to the local dealer, where it was diagnosed that the vacuum pump had shattered. The vehicle was repaired, but the failure recurred. The contact reached out to a GMC engineer, who informed the contact that the failure was due to the camshaft reluctor. While driving, the vehicle lost engine power. The vehicle was towed to the same local dealer, where it was diagnosed that the throttle body needed to be replaced. The vehicle was repaired, but the failure recurred. The vehicle was towed to the local dealer, where it was diagnosed that the turbo code had a mass air flow sensor failure. The vehicle was repaired. While driving at an undisclosed speed, the check engine warning light illuminated, and the reduced engine power message was displayed. There was blue smoke detected from the exhaust. The vehicle was towed to an independent mechanic, who informed the contact that the throttle had failed. The vehicle was towed to another local dealer, Power GMC Chevrolet of Newport (1422 N Coast Hwy, Newport, OR 97365) where it was diagnosed that the air pipe charge and air cooler needed to be replaced. The vehicle was repaired. The manufacturer was contacted and referred the contact to the local dealer. The failure mileage was approximately 50,000.

Mileage: 50,000

This Saturday morning driving my family to Bradenton as I was coming off the hwy to my exit when I experienced a brake fail I thought, brakes got real hard and I couldn't stop the car on time like I wanted to, so I had to press the brakes pedal harder to come to a complete stop, three different places no one knew what could be the problem until I took it to GMC dealership they can only give a code P0556 / U0401 SERVICE BRAKE ASSIST, seems it was too late to checked out they where about to close , something to do with the busters not sure yet but it's getting checked out tomorrow morning, I was driving on cruise control at a speed limit when this happened, will let you know what's the result of my situation.

Brake booster failed with no warning. Brake pad was hard to push down as I exited the freeway. I came close to hitting the vehicle in front of me which would have resulted in a bad car accident. There were no warning. This is extremely dangerous and is a risk to not only the driver but also to vehicles in the path of a vehicle that cannot stop. This needs to be a recall along with the other vehicles that have a recall for this part.

Heard a ticking noise coming from the engine compartment. I opened the hood to investigate which I first check oil level as sounded like a lifter making the noise but all fluid levels was normal. I drove home and 3 miles later ticking noise went away and my adaptive brake assist came in and the brake pedal was hard to press. Luckily I lived another mile down the road so I got the car home and safely parked it. One of the symptoms is hearing a ticking noise from engine when a braking component fails. Further learned could be a vacuum issue which needs a software update which makes no sense. Had I been traveling highway speeds when this happened this story could have a had a very different tragic ending. Car has less then 53000 miles on it

Driving down the freeway and all of a sudden got a service break assist notification and without warning I was unable to stop the vehicle. I was able to coast my way off the freeway and upon my exit I tried to pull into an empty parking lot but there was a fire fence I ended up crashing into which is probably what brought the vehicle to a complete stop. This is very dangerous and I have read numerous complaints from other 2020 terrain owners who have experienced the same problem. Mechanic stated I need need vacuum pump for brake booster which of course my warranty doesn’t cover. Something seriously needs to be done about this. My accident could have been a lot worse

I was driving on the interstate when my brakes went out. I was able to get off at and exit and pull into a gas station but had to put on the emergency brake.

While on highway service brake system warning light came on,brake became hard to apply almost causing an accident. Vehicle had to be towed to a repair shop(dealer).after paying over $1600 the problem was not resolved and found there are numerous complaints about issues with the terrain and no recall issued.are they waiting til someone dies before a recall?

I was driving down The expressway. The traffic in front of me came to a stop. When I went to apply the brakes I had no breaks. The pedal was as hard as A rock So when I realized I couldn't stop I swerved over into the breakdown lane. And continue to pass cars at a high rate of speed until I got the car to stop. There were no check engine lights on Then I had the car towed to the Dealership Where they tell me is a break vacuum pump. That has damaged The Cam shaft. Pistons and rods in the engine. Totaling $7200. In damage. No one seems to care and I still owe 20000 on the car. Car has 71000 miles on it.

The brake system is only working at about 5%. There are known defects with other GMC models of this year and this vehicle should be reviewed .

Service brake assists light flashes on dashboard . Steering wheel locks up and jerk’s loose suddenly when making a right turn, in these moments when the steering wheel jerks loose ;hands are off taken off the steering wheel otherwise injury can occur. Battery life 2 -yrs old is not performing optimally. Can not hold a sufficient charge and ESC light flashes. Vdnt valve leaks discovered.

My service brake assist light came on and then within seconds my vehicle then said engine power has been lowered and my vehicle pretty much shut down no steering no brakes couldn't do anything. Took it into the repair shop and my vacuum pump has shattered and now damaged my camshaft. I am aware there's been many other vehicles recalled with GM's vacuum pumps and I'm not sure why my year and model has not been included when it's doing the same thing and not to mention I have seen countless other cases of people saying same things happen to them with their GMC terrains.

UNKNOWN...ACTS AS IF ITS A SMART CAR THAT'S NOT REALLY A SMART CAR

Brakes hard to press. Almost cause an accident on interstate. Was able to contain vehicle. Took to autozone to assessed and it said Powertrain System. Brake Booster Senor Circuit.

The contact owns a 2020 GMC Terrain. The contact stated while driving at various speeds, the vehicle lost brake functionality while depressing the brake pedal. The contact stated no warning light was illuminated. The vehicle was towed to a local dealer where it was diagnosed with needing the vacuum pump replaced. The vehicle was repaired however, the failure persisted. The manufacturer was not informed of the failure. The failure mileage was approximately 40,000. The VIN was unavailable.

Mileage: 40,000

SERVICE BRAKE ASSIST MESSAGE CAME ACROSS SCREEN AFTER I WAS UNABLE TO PUSH DOWN BRAKE PEDAL.

Mileage: 28,830

WHEN REVERSING OUT OF A PARKING SPOT, BRAKES FAILED CAUSING ACCIDENT. MULTIPLE ATTEMPTS TO DEPRESS BRAKE PEDAL WITH NO BRAKING. HIT A PARKED CAR. AFTER SHUTTING CAR OFF AND ATTEMPTING TO MOVE VEHICLE BRAKES DID ENGAGE AND RESPOND CORRECTLY. REAR DAMAGE TO TERRAIN OCCURRED REQUIRING TOWING.

Mileage: 457

EVERY WEEK IT'S SOMETHING DIFFERENT. IN MOTION... NO CRUZE CONTROL. NO AUDIO. DON'T DRIVE OVER 50MPH BRAKE PROBLEM. PARKING BRAKE ENGAGES RANDOMLY AND WITHOUT USER ENGAGEMENT. NO AWD. NO STABILITY TRACTION. THIS HAPPENS SO FREQUENTLY THE DASH INDICATORS HAVE BEEN REDUCED TO 'IDIOT LIGHTS'. AT WHAT POINT DO I BECOME CONCERNED? THINGS APPEAR TO RESOLVE WHEN THE ENGINE IS TURNED OFF AND BACK ON, SOMETIMES....I COMPARE IT TO OTHER GLITCHY TECHNOLOGY. HOWEVER I POTENTIALLY COULD BE AT AN 80MPH CRAZING SPEED WHEN I DECIDE TO IGNORE THE IDIOT LIGHTS...WHAT HAPPENS WHEN A REAL PROBLEM PRESENTS AND I IGNORE THE DASH INDICATORS DO TO FREQUENT GLITCHES? I'M SO DISAPPOINTED. MY 2 PREVIOUS TERRAINS WERE 10 TIMES THE VEHICLE THE 2020 MODEL YEAR.