GMC Sierra Complaints (2020)

626 consumer complaints on file.

#11725965March 20, 2026
POWER TRAIN
My truck has been exhibiting hard downshifting at certain speeds, when the powertrain loads up such as a grade change, and requires a downshift. I have complained about this issue to the dealership as early as 2022, and 33,185 miles. The dealership made me pay for a transmission $388.90 flush which did not resolve the issue. The problem has become progressively worse, to the point where the toll road transponder fell of my windshield during a recent harsh downshifting incident. At the same time there was an existing MIL and derating for a DEF heater and NOx sensor failure, so during a warranty visit I asked that this transmission issue be addressed. On Friday March 13, the dealership called and said they confirmed the hard downshifting, albeit not as extreme as I described. The technician said that the valvebody needs to be replaced. At the same time, they performed a TCM flash for the 10L1000 momentary wheel lockup recall. The dealership then said they could not get the truck to set a P0747 code, said that GM refuses to replace the faulty valve body, and recommended I take the vehicle home unrepaired, and to come back when the P0747 code is set. I requested they continue to drive the vehicle. Today March 20 the dealership called and said they could not get the code to set, and that I need to drive the truck and come back when the code appears, despite the truck exhibiting clear symptoms of a progressively wearing feed limit low valve. N242454441 does NOT seem to indicate a P0747 code is required to replace the valve body. This vehicle is not safe for towing a 20,000+lbs and GMC is refusing to repair a transmission with symptoms congruent with N242454441. The dealership still has possession of the vehicle and wants $360+ in diagnostic labor.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11725605March 19, 2026
ENGINE
The 10L80 transmission had a catastrophic failure just outside of the GM warranty. At under 70K miles the pump gears came apart and sent metallic debris throughout the entire transmission and exhaust gaskets converter next to the transmission. These will need to be replaced. I have found multiple cases online with this 10L80 transmission where there has been significant problems with these transmissions blowing up or even causing momentary lockup with the wheels. This transmission is notorious for problems but has not yet been recalled. My mom and nephews were in the vehicle when it broke down putting their safety at risk on the the highway. This problem was confirmed by the GMC dealership here in Ruston, LA. The dealership has done the mechanical inspection. The engine started making an extremely loud noise and the warning lights did not even come on until I attempted to start it later after the breakdown.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11725236March 18, 2026
ENGINE AND ENGINE COOLING:EXHAUST SYSTEM:EMISSION CONTROL:UREA INJECTION SYSTEM (DEF)
The contact owns a 2020 GMC Sierra 1500. The contact stated that while starting the vehicle, the engine hesitated while turning over. The vehicle started with the check engine warning light illuminated, and the DEF (Diesel Exhaust Fluid) sensor light was illuminated. The message “94 miles before vehicle enters LIMP Mode" was displayed and instructed the contact to see the Diesel Exhaust Fluid section of the Owner's Manual. The vehicle was restricted to a 65 MPH max speed. The vehicle was towed to a dealer, where it was diagnosed, and it was determined that the DEF tank pump assembly had failed and needed to be replaced. The vehicle was not repaired. The manufacturer was not notified of the failure. The failure mileage was 121,000.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11724546March 16, 2026
ELECTRICAL SYSTEM:INSTRUMENT PANEL:SPEEDOMETER/ODOMETER
Odometer Fraud. The contact attempted to purchase a 2020 GMC Sierra 1500. The contact discovered a mileage discrepancy. The vehicle was a private sale. At the time of purchase, the mileage was 75,000. At the time of registration, the Carfax Report indicated that the mileage was 175,000.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11724575March 16, 2026
ENGINE
Vehicle has 28,000 miles and auto shop states that the engine is blow, it's knocking and vibrating throughout the engine.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11724457March 15, 2026
ENGINE
Engine failure at 84000
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11724149March 13, 2026
ELECTRICAL SYSTEM, ENGINE
I was driving the truck on the freeway and the engine completely shut off with no warning. I pulled to the side of the shoulder and I could smell a burning smell. The truck wouldn’t start back up or move in neutral. Towed it to a shop and they said it had a camshaft issue and a slight knocking noise when they got it to fire up only would run for a little then shut back off. Now I’m having to replace the whole engine due to being bad with the cam code and knocking.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11723896March 12, 2026
ELECTRICAL SYSTEM
The backup camera is too bright at night and therefore useless . Tried searching the web but found no fix that would actually work. Took my truck to the dealer and they never heard of this issue even though there are numerous articles about it on the world wide Web.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11723707March 11, 2026
ENGINE
February 28th 2026, I was driving on the highway with my children and suddenly without any prior warning my cars check engine light came on. It immediately starting losing power, made a knocking noise, and sounded like it was misfiring. Fortunately I was able to make it safely off the highway and have my car towed to the dealership. This was most definitely a life threatening situation which no one should have to face. The dealership dismantled my engine and i was advised the engine had an internal failure due to the valve lifter , rods , and camshaft damage. When looking online there are many complaints and lawsuits regarding this investigation of GMC’s 5.3 engine. I believe this was due to catastrophic damage of the components and there needs to be a recall regarding this issue. The car has always been properly serviced and regular oil changes.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11723197March 10, 2026
POWER TRAIN
While driving down a highway doing between 45 and 55 mph the transmission suddenly and completely faulted causing the truck to come to a complete stop. Just enough power to get to the shoulder luckily. The transmission had basically completely blown out, fluid everywhere. The insurance company did not find any comprehensive damage. The entire transmission needs to be replaced. There were no indicators showing any problems, no alerts, no warning whatsoever. Mechanics said there was a lot of metal coming out of the transmission. The truck is currently in a mechanic shop awaiting the new transmission, so at this time it is available for inspection. The safety issue here is that it happened on a busy highway, and the vehicle was no longer drivable so it needed to be towed causing more time spent on the side of the road.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11723067March 9, 2026
ENGINE
While driving, my vehicle experienced a sudden and complete engine failure without any prior warning. There were no warning lights, dashboard alerts, or performance issues that would have indicated an impending mechanical problem. The failure occurred unexpectedly while I was actively driving on a public roadway. After the incident, the vehicle was inspected and diagnosed by a licensed mechanic. The diagnosis determined that an internal engine lifter failed, which subsequently caused damage to the camshaft. This type of failure appears to be the result of an internal mechanical defect rather than any form of neglect or improper maintenance. The abrupt nature of this engine failure created a serious safety hazard. The vehicle suddenly lost the ability to operate normally, forcing me to slow down and stop in active traffic. This unexpected loss of power placed my safety, as well as the safety of other motorists on the road, at significant risk. A critical engine component failing without warning while the vehicle is in operation raises serious concerns about reliability and safety. The vehicle has been properly maintained throughout ownership. All routine maintenance and servicing have been performed by licensed mechanics, and I can provide complete maintenance records documenting this history. At no point prior to this incident were there any signs, warnings, or diagnostic alerts indicating an issue with the engine. The vehicle has already been fully inspected and diagnosed by a licensed mechanic, and the findings are available for review. If necessary, arrangements can be made for the manufacturer or an authorized representative to inspect the vehicle and verify the damage. Given the sudden nature of this failure, the internal engine damage involved, and the safety risk it created while driving, I am requesting that this issue be formally reviewed and addressed by the manufacturer.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11722264March 5, 2026
STEERING, POWER TRAIN, ENGINE
Hi, was driving Vehicle GMC 1500 Denali, vehicle Lost power, all Lites lite up on Dashboard, Vehicle Just lost power and i swerved off Road and sideswiped a Plant Holder on side of Road, damaging side passenger Rear door. I bought the truck to GMC Rvc and they said vehicle Blew Cam shaft and Lifters. I explained to them I'm very concerned for others safety in these Vehicles with the 6.2 Engine. Someone is going to get Killed or even a family. I did look up this vehicle its not listed in Recall, but this vehicle has same engine as ones in Recall. Rvc Gmc issued me a bill for repairs for the amount of $8185.20 and they stated they took 3k off invoice. I did Pay total Invoice....I'm just asking you to please look into this as this is defiantly an issue and this year should be listed on Recall as well.. Thanku for at least looking at this. My cell is [XXX] if you need to reach us...Thx.... INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)
Crash:
Yes
Fire:
No
Injuries:
0
Deaths:
0
#11722311March 5, 2026
SUSPENSION
My 2020 GMC Sierra Denali diesel with approximately 90,000 miles experienced two separate front suspension failures within a short period of time. The driver side tie rod and wheel hub failed first and required repair. Shortly after, the passenger side front suspension failed in a similar way and the vehicle had to be towed. These failures caused the front wheels to become unstable and created a serious safety concern while driving. Suspension components such as tie rods and hubs should not fail at this mileage under normal driving conditions.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11721474March 2, 2026
ENGINE AND ENGINE COOLING
The contact owns a 2020 GMC Sierra 1500. The contact stated that while driving approximately 40 MPH, the check engine warning light illuminated. The vehicle was taken to a dealer, where it was diagnosed, and determined that the oil pump solenoid needed to be replaced. The vehicle was repaired, but after the repair was performed, the engine seized. The manufacturer was notified of the failure. The failure mileage was approximately 45,000.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11721569March 2, 2026
ENGINE
At 96,000 miles (3,000 miles after the extended warranty expired), I noticed the "GM tick" more prominent and had more of a metallic sound than it ever did. Upon further investigation, it was found that a collapsed lifter may be the culprit. The truck was brought to the dealer and it was confirmed that the #1 hydraulic lifter had collapsed and needed replacement. This work was approved and tonight, I received a call from Rivard Buick GMC saying that the collapsed lifter also caused significant wear on the camshaft which also now requires replacement. Loss of power on the road poses a significant risk as I carry my children in the vehicle. No warning lamps, messages, or other indicators appeared before or when the issue occurred. The issue was reproduced by the manufacturer/dealer. The dealer Service Manager confirmed that this is extremely common with these trucks with the 6.2L engine and said it was a design flaw due to Dynamic Fuel Management, as well as the oil viscosity recommendation from GM being too low. The year group before and after the 2020 has been recalled along with TSB's issued, however, this group is not part of it. I contacted GM Customer Service (Case [XXX]) and was offered a 10% discount on the repair, being told that this is a "great deal considering the vehicle is out of warranty". GM Customer Service has now resorted to not answering any further questions after several attempts to reach someone. This is also after replacing the 10-speed transmission that was also not part of any recall but that was such an issue that the dealer was only able to source used transmissions rather than new parts. Clearly GM won't make the right decisions to back their products or customers, so NHTSA intervention is necessary. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11721241March 1, 2026
ENGINE
The motor went to knocking and lost power. Cost us about 3500. To fix. Lifters went down cam went down which caused major motor knock and loss of payer
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11720886February 27, 2026
STEERING, ENGINE
The contact owns a 2020 GMC Sierra 1500. The contact stated that while driving at various speeds, the steering wheel became stiff and difficult to steer to the left or the right. The power steering and check engine warning lights were illuminated. The vehicle was towed to a local dealer, where it was diagnosed with a corroded body ground strap. The error codes were cleared, and a test drive was performed. The vehicle was repaired out of pocket. Upon further investigation, the contact related the failure to the GMC Customer Satisfaction Program: N252515590; however, the VIN was not included. The manufacturer was not made aware of the failure. The failure mileage was approximately 37,061.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11720842February 27, 2026
POWER TRAIN
Vehicle is shifting hard when switching gears. Typical with the recall and the valve body being the issue. Dealership is saying it is not covered by recall.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11720829February 26, 2026
ENGINE
Misfiring due to DFM which is a common issue. Running a scan confirmed. I have installed a AFM/DFM disabler which seems to fix the issue.
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0
#11720059February 24, 2026
ENGINE
Have not had my truck in over a month while it’s getting repaired had engine failure sure to faulty hydraulic lifters and camshaft failure due to the Dynamic fuel management system purchased warranty for my vehicle but this needs to be looked into it is unfair as a consumer that they are not doing anything about 2020 models and earlier they are just focusing on 2021 and up. They almost had me crash my truck due to power loss
Crash:
No
Fire:
No
Injuries:
0
Deaths:
0

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