2020 GMC Sierra 3500 Owner Complaints

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.

NHTSA ID

11725965

Incident

Mar 12, 2026

Diesel exhaust fluid tank heater malfunctioned and meted tank and connectors.

NHTSA ID

11712433

Incident

Jan 12, 2026

Known defect with 2019 and now 2020 GMC sierra trucks. Design was updated for 2021+ which has corrected the seal failure defect. GM has issued a service bulletin to dealers about how to repair the problem. Back window is leaking water. Defective seal noted by GM. GM is only covering the cost of repair if. Vehicle is still under 3/36 warranty. If outside your warranty cost from dealer to owner is $2500 to $6000. A known design failure GM recognized and took steps to change the design for future. Vehicles but will not stand behind vehicles that have this defect. Would like the cost to the repair fall back to GM to cover. Bulletin # 18NA383 [XXX] INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA ID

11693845

Incident

Oct 1, 2025

the engine seized at 65mph. available for inspection. was left stranded in a limited access area with no cell service. there was no warning, the engine just stopped at highway speed and would not restart. the problem was confirmed by an independent service center. they couldnt identify which component had failed without a costly teardown. occurred at 112,000 miles, past the 100,000 mile powertrain warranty.

NHTSA ID

11691992

Incident

Aug 28, 2025

The contact owns a 2020 GMC Sierra 3500. The contact stated that while driving at an undisclosed speed, the vehicle inadvertently went into LIMP Mode. There was no warning light illuminated. The vehicle was taken to the dealer, where it was diagnosed that the transmission valve body sensor had failed and needed to be replaced. The vehicle was not repaired. The manufacturer was made aware of the failure and referred the contact to the NHTSA Hotline for assistance. The approximate failure mileage was 130,000.

NHTSA ID

11672242

Incident

Jul 9, 2025

Mileage

130,000 mi

The contact owns a 2020 GMC Sierra 3500. The contact stated that while driving at 60 MPH, the rear differential seized, in addition, the contact was hauling a median size tracker on top of a flat bed. The flat bed jackknifed and hit the left side of the contact's vehicle. The vehicle was able to come to a stop. The air bags did not deploy. There was no warning light illuminated. A police report was filed. There were no injuries sustained. The vehicle was towed to a towing yard. The trailer was towed to the residence. The tractor was damaged in the accident. The vehicle was diagnosed by an independent mechanic. The contact was informed that the transmission had failed. The vehicle was not repaired. The insurance company was contacted. A claim was filed with the insurance company, and it was canceled a few days later by the insurance company. The manufacturer was not notified of the failure. The failure mileage was approximately 108,000.

NHTSA ID

11672009

Incident

Oct 2, 2024

Mileage

108,000 mi

The contact owns a 2020 GMC Sierra 3500. The contact stated that while driving 45 MPH with passengers seated in the rear seats, the passengers became aware that water was entering the vehicle between the window and frame. There were no warning lights illuminated. The vehicle was taken to the local dealer, who informed the contact of Technical Service Bulletin: 18-NA-383. The vehicle was not diagnosed or repaired. The manufacturer was contacted and confirmed that there was no special coverage or warranty coverage on the vehicle. The contact was referred to the NHTSA Hotline for assistance. The failure mileage was approximately 50,000.

NHTSA ID

11670439

Incident

Jun 10, 2025

Mileage

50,000 mi

LT275/65R20 While driving Westbound on I87/US64/US264 at the on ramp of US64 business at highway speeds, the driver’s side rear tire tread de-laminated from the belts of the tire. Observed the entire tread airborne in rear view mirror. Pulled over to shoulder and observed for damage to other vehicles, no vehicle was hit but drivers did have to make evasive maneuvers to avoid debris. Tire remained at required PSI, thus did not deflate. Drove vehicle ¼ mile to ** exit to look for safe parking. Called AAA and had vehicle towed to residence. No police report filed. Reported incident to insurance agent in the event of a subsequent damage claim by other drivers. Tire was inspected by ** Tire and confirmed tread had indeed de laminated from tire core. Clear failure of factory tire mounted on factory wheels with no suspension or drive train modifications. Vehicle was totally stock at time of the incident. The safety of the other drivers on the road could have been significantly impacted had the tread hit their windshield or front tire. The violence of the tire separation was similar to an impact with large road debris. The vehicle suffered significant damage to the drivers side truck bed, bumper, sensors and wheel-well. Local tire company confirmed failure mode of tire. Vehicle had received required annual NC State safety inspection, by certified inspection station, including tires on April 30, 2025. There were no warnings prior to incident, visual or audio. The tire(s) involved are available for inspection, as owner has retained all 4 tires at time of replacement.

NHTSA ID

11670235

Incident

Jun 27, 2025

Engine started skipping, then service parking brake light came on, then service engine light came on and speed dropped to 44 mph.

NHTSA ID

11662257

Incident

May 21, 2025

My IntelliBeam function stops working sometimes, I can still use the lights as normal but the IntelliBeam function stops every so often and starts working after about 2 to 10 mins. Lane departure warning stops every so often and will start working after 1 to 10 mins, I have noticed that when it stops working at night time then the IntelliBeam function stops working also. When I press the on/off button for lane departure then it will say that lane departure is unavailable right now. I have been getting a p20ee code showing something is wrong with SCR nox sensor 2. Scan tool reveals that the sensor works normal and then stops. Once I clear the code then it works good for a few days.

NHTSA ID

11661486

Incident

May 16, 2025

Valve body failed while pulling my camper down the interstate. Transmission began to have issues and locked up on us while driving. Luckily i was able to avoid any accidents. Had truck towed to a private Transmission shop to have the transmission repaired. Shop advised the failure was due to the faulty valve body.

NHTSA ID

11654874

Incident

Feb 9, 2025

Def heater connection on the tank will arc and melt down causing engine derate and costly repairs. Gm know and has released a service bulletins in 2022. Bulletins N212342980. But even with bulletins done still fails. And talking todealer ships it a very common problem and there is a shortage in parts.

NHTSA ID

11648405

Incident

Feb 28, 2025

Greetings. In December 2024, I brought my vehicle in for the rear end lock up recall. The recall reprogrammed the transmission control module. As admitted, by yourself and GM this doesn't fix the problem. In addition, if the lockup occurs and a new valve body is required, GM is on back order with no date for delivery. Also, it is replacing it with the same valve body, i.e. you will have the same problem in the future. Nextgen Drivetrain has a valve body for around $1000 that fixes the problem. [XXX] . Please read the attached blog from Nextgen, they explain in detail, the problems and the fixes. I am scared to death to pull my travel trailer out of state with this looming problem. Please give us a better solution. Thank you. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA ID

11648300

Incident

Dec 10, 2024

The contact owns a 2020 GMC Sierra 3500. The contact received notification of NHTSA Campaign Number: 24V797000 (Power Train); however, the part to do the recall repair was not yet available. The contact was concerned about the remedy repair not being adequate to repair the vehicle. The local dealer was contacted. The contact stated that the manufacturer had exceeded a reasonable amount of time for the recall repair. The manufacturer was made aware of the issue. The contact had not experienced a failure. Parts distribution disconnect.

NHTSA ID

11646537

Incident

Mar 5, 2025

I was towing my 44'camper entering the highway and during excellration there was a loud bang and the truck shuddered no lights on the dash. Pulled over and did a visual check of the vehicle and did not see anything out of ordinary. Continued on our journey and during the the week noticed clunking noise when shifting into park and into drive with no camper. We shortened our trip and returned home with no futher incidents. Received recall letter from GM in December, called the dealer and was told Gm has not released my VIN number yet. Called twice in January 2025 and the software was done on February 20, 2025. Truck seems to run as it should. I use the truck for business and to tow my camper. The software is only a patch. My fear is I'm out traveling with my 44' camper and the truck goes into limp mode limiting to fifth gear. Then I have to get the truck towed home and the camper. I travel with 3 dogs too. GM has known about this issue and has failed to fix the problem leaving me and my family at risk of a serious accident. I can not work without my truck and GM does not care about me or my family. I have several camping trips scheduled for this year and I'm considering canceling them because I don't feel comfortable with the software update.

NHTSA ID

11645490

Incident

Nov 26, 2024

Engine Coolant Low error constantly appears. GM Service provider states that engine coolant level is fine, but sensor may be defective.

NHTSA ID

11639548

Incident

May 12, 2023

Contacted General Motors to have the Recall software patch installed, appoint was set, vehicle was dropped off and now they are telling me there is nothing they can do, that the recall is not available. The software update is available, and is being installed on other vehicles. This is a life safety issue as the rear wheels can lock up at any time which could cause a vehicle accident involving the vehicle under recall as well any vehicles on the road around this vehicle when it happens. General Motors should be taking care of this asap instead of waiting. I do not feel safe driving the vehicle until they feel like they installing it.

NHTSA ID

11634795

Incident

Oct 24, 2024

The contact owns a 2020 GMC Sierra 3500. The contact stated that while towing a trailer, the tailgate unintendedly opened while making a right turn. Due to the failure, the end of the tailgate was ripped in half. Upon investigation, the contact discovered NHTSA Campaign Number: 24V060000 (LATCHES/LOCKS/LINKAGES); which was linked to the failure. The vehicle was taken to a dealer and was informed that the vehicle was not included in the recall. The manufacturer was notified of the failure and referred to the NHTSA Hotline to report the failure. The vehicle was not repaired. The failure mileage was approximately 43,000.

NHTSA ID

11631616

Incident

Jun 11, 2024

Mileage

43,000 mi

The tailgate automatically opened while I was driving. I was sure the tailgate was shut and latched properly prior to the incident.

NHTSA ID

11631170

Incident

Dec 16, 2024

The contact owns a 2020 GMC Sierra 3500. The contact stated while driving approximately 60 MPH, the vehicle jerked, lost motive power, and almost stopped unintendedly. There was no warning light illuminated. The contact was able to pull into a parking lot, where the vehicle shut off. The contact stated that while attempting to restart the vehicle, the diagnostic trouble code: P129F was displayed, and the vehicle failed to restart. The vehicle was towed to the residence. The local dealer was contacted and advised the contact that the failure might be related to the fuel pump control module and that the part was on backorder. The vehicle was not diagnosed or repaired. The manufacturer was notified of the failure. The failure mileage was approximately 19,000.

NHTSA ID

11627460

Incident

Nov 25, 2024

Mileage

19,000 mi

I have a complaint about the recall response from both nasal and gm. I feel the cure is substandard. Why not just put new transmission control modules in to correct this problem. Very disappointed

NHTSA ID

11626032

Incident

Nov 2, 2024

There is a current safety recall N232426400 on GMC pickups including the year of my truck. GMC is saying that my VIN is not covered by the recall. However, I have the multi-pro tailgate and it came open about 6 months ago on its own as i was backing up and it caused me to run into my trailer with the tailgate. I put my tailgate up after moving my truck from under my trailer and then when i went to back up somehow the tailgate popped open and i didnt know and it contacted the top of tailgate while it was down.

NHTSA ID

11605969

Incident

Mar 7, 2024

driving 65mph on interstate, attempted to change lanes to pass slower vehicle and pressed upon accelerator pedal...truck violently skidded to a stop and sent me onto shoulder, many vehicles behind me swerved to avoid my vehicle. GM wont repair and says since they cant replicate its not really happening. this has happened twice in last 2 weeks.

NHTSA ID

11602485

Incident

Jul 15, 2024

driving approximately 50 mph when vehicle suddenly made loud bang and locked up rear brakes for 25' coming to a stop in road side ditch, numerous vehicles had to make evasive actions to avoid me and other vehicles. flat spotted tire abut no visible physical damage. sat on side of road for transmission temp to cool down then drove to shop without repeat. called dealer was told the earliest appt was a month away. have not been able to repeat incident so far. this has happened a few times and is becoming more frequent, mfg has tsb issued but indicates they cant assist because my warranty has expired so i will have to pay 225 per hour diagnostic fee. this is untenable and dangerous. this needs a recall and repair ASAP.

NHTSA ID

11598428

Incident

Jul 1, 2024

driving 45 mph westbound i70 at eisenhower tunnel, vefhicle made loud bang, brakes locked up momentarily slowing vehicle to around 25mph. multiple vehicles had to make evasive manuevers to avoid collision. vehicle released after a 15FT skid. pulled over to safety and inspect for damage, tires were falt spotted but no damage was visible. called dealer servcei and was told to make appt and set for diagnostic. service could not replicate or find damage so I was sent on my way and told if it does it again let us know. I am scared to drive this vehicle its unsafe

NHTSA ID

11598426

Incident

Mar 30, 2024