2020 GMC Sierra 3500 Problems

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.

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.

Vehicle will not start due to known GM issues. This failure left my family stranded in cold dark unsafe area once already. If we were in the flow of traffic or had to leave an area immediately we would have been unable too. Known GM issue, engine fault code P12A6 fault code. Bulletin: PIP5719A discusses this issue. I am being told by the dealer there is a newer bulletin which advises ECM update. GM dealer is stating ECM software upgrade is required to resolve at owners expense. Owner is responsible for diagnostic fee in addition to repair costs. If the issue is not resolved vehicle may continue to experience starting failure and or other electrical problems. The night the vehicle left us stranded instrumentation was erratic and not reading properly on the instrument cluster. Very unsafe and GM should reach out to customers to inform them a software update is needed and it should not be at the expense to the consumer if the consumer is out of the bumper to bumper warranty.

Plugged in engine block heater and the car erupted in flames. Total loss.

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

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.

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

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.

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.

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.

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)

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.

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.

The contact owns a 2020 GMC Sierra 3500 equipped with Goodyear Tires, Tire Line: Wrangler Trail Runner, Tire Size: LT275/65/R20), DOT Number: (NA). The contact stated that while driving approximately 40-45 MPH, the vehicle exhibited the death wobble, causing the vehicle to become difficult to steer. The contact took the vehicle to the dealer to have the wheels aligned; however, the contact was informed of tread separation on the front driver’s side tire, and that the driver’s side rear tire had bubbles. The contact was informed that the passenger’s side front and rear had bubbles as well. The tires were replaced with a different brand tire. The manufacturer was not made aware of the failure. The approximate failure mileage was 29,400.

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.

Rear sliding window is leaking water into the cabin

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.

Rear tires locking up out of no where almost made me jack knife.

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.

The contact owned a 2022 GMC Sierra. The contact stated that while her husband was driving at an undisclosed speed, the vehicle collided head-on with another vehicle that ran a red light. The air bags did not deploy. No warning lights were illuminated. A police report was filed. No injuries were reported, but the contact and her husband sought medical treatment for various bruises caused by the seat belt at a later date. The vehicle was not taken to the dealer or an independent mechanic but was instead towed to a tow yard. The vehicle was not repaired. instead deemed a total loss. The manufacturer was not notified of the failure. The failure mileage was 25,000.

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.

I had a blow out on my rear tire on my 2020 GMC Sierra 3500 AT4 truck while travelling down the highway while pulling my 43 foot RV fifth wheel toy hauler. The vehicle had 21,000 miles on it. The tires and wheels are Goodyear Wrangler LT275/65R20 E rated tires. The problem is i changed the tire to find i had a a MICHEllin LT 275/70R18 tire for a spare that i changed. This effected the ABS and was hard pulling my RV back home for another 40 miles. Under NHTSA Campaign number 21V578000 GM recall number N212329780 there was an issue with the spare tire in the sierra 1500 and 2500 trucks but not mentioned in the 3500. This was a huge safety issue for us to pull the truck home as we had to drive at 35 mph for 40 miles on the highway. GM should not be putting a smaller tire/wheel as a spare on a large truck. One side is significanlty lower than the other when the two different tires are on the back of the vehicle.

VEHICLE EXHIBITS STEERING WHEEL SHAKE / SHIMMY AT SPEEDS ABOVE 50MPH, SOMETIMES SEVERE. REPEATED ATTEMPTS AT REPAIR (CURRENTLY 4 DEALER VISITS), INCLUDING APPLICATION OF SERVICE BULLETIN 19-NA-240 DOES NOT CORRECT THE PROBLEM. GM HAS NOW INDICATED THIS IS A "NORMAL" CONDITION, AND WILL NOT AUTHORIZE FURTHER WARRANTY REIMBURSABLE LABOR FOR CORRECTION TO DEALER. THIS STEERING CONDITION AFFECTS SAFETY AS IT OCCURS IN VARYING SEVERITY AND WITH NO WARNING, ESPECIALLY DURING DRIVING OVER ROUGH PAVEMENT / BUMPS, AND HAS NEARLY LEAD TO A LOSS OF CONTROL OF THE TRUCK. THIS CONDITION WAS PRESENT AT DELIVERY OF TRUCK AT 221 MILES. TRUCK CURRENTLY HAS 1688 MILES.