The component that has failed is the engine coolant flow control valve AC Delco part number 55516369. Unfortunately the part is still installed on the vehicle. It has been taken to a dealer and this is a known issue but no recall has been issued. The check engine comes on sometimes but not always, sometimes the pickup has plenty of power to drive and sometime it will barely pull itself, all in the same trip without shutting the ignition off. The symptoms first started in December of 2023, but were sporadic, now it is nearly everytime the pickup is started. It is extremely dangerous to drive this vehicle when it has a problem. You cannot tell if it will accelerate normally or is you will push the pedal and it does nothing. The part to repair the problem is on backorder and no release date is yet available. We have been waiting for 3 months and still no word on when this will be repaired.

- Cimarron, KS, USA

I purchased this vehicle used with approx 16k miles on it. Not long after getting it - as I was driving it started dinging and then would shut off. Sometimes I-??m in the fast lane going 75Mph and it-??ll just shut off. The dealership can-??t get it to repeat itself. They said they-??ve heard of it happening before but it throws different codes. There-??s no rhyme or reason to causing it to shut off, but here lately I don-??t even get the warning bell. It just dies on me. As soon as i shift it to neutral and press start it-??ll restart instantly. But it-??s scary nonetheless, and causes me to drop speed instantly and poses a safety risk especially when I have semi-??s or other vehicles close behind.

- Meridian, OK, USA

"Service parking brake" "steering assist is reduced drive with care" comments showed up on screen-??check engine light on, truck shaking/ vibrating completely as if wanting to turn off this all happened while driving on the road and randomly happened-??please help..very Concerned

- Edinburg, TX, USA

Lifters camshaft malfunction. Known issue with 2021 GMC Sierra 20,000 miles

- Columbia, SC, USA

After having simple oil and filter, and engine and cabin filter replaced at Alpine Buick GMC in Colorado Springs, CO, I received my vehicle back and noticed a complete difference in performance. It hesitates when accelerating, stays low in every gear, and bounces, and I mean bounces hard, when shifting gears, especially slowing down. When slowing down, as it shifts to the next lower gear, it almost pushes the truck forward against me pushing the breaks. Then, when feathering to accelerate slowly, it almost bounces back up to speed, hesitating until I let off the accelerator pedal a little, and it immediately shifts to about 1000 rpm in gear. I have to push really hard for it to go up a gear, and when it does, it has lost all power. My vehicle doesn-??t run right anymore after my service appt. I have brought it to my hometown dealership and they say it runs fine and nothings wrong. But there is something wrong with it.

- Winter Haven, FL, USA

The contact owns a 2021 GMC Sierra 1500. The contact stated that while driving at an undisclosed speed, the vehicle was shaking with the check engine warning light illuminated. The independent mechanic was made aware of the failure; however, the vehicle was not diagnosed or repaired. The contact stated that the independent mechanic had previously replaced the lifters, but the failure recurred. The manufacturer was not made aware of the failure. The failure mileage was approximately 20,095.

- Dodge City, KS, USA

While driving home from work around 6 am, my car had multiple warning lights and warning messages come up all of a sudden. Immediately after that I lost my power brakes and steering and was not able to control my car at 40 mph. I was lucky the light I passed was green and there was no other traffic. I was able to bring my truck to a stop after more than a quarter mile by putting all my weight on the brake pedal. The truck was towed to the dealer and has been there ever since.

- Coral Gables, FL, USA

Driving down the highway the engine started skipping and started blowing out black smoke, and quit running in the middle of the highway. Found out the had a factory lifter defect on my model and a service update was supposed to be done on the truck changing out the lifters however even though I have gone to dealership for all the maintenance the service had never been done or told to me. This could have been very dangerous just engine failure the service by GMC N212353840

- Panama City Beach, FL, USA

I was operating my vehicle in northern Minnesota with a temperature well below freezing. Vehicle warning light came on that said "turn off vehicle" which I did. When I went to start it again it would not turn over. It appeared that a large amount of oil had expelled from the vehicle. It was very dangerous as I was in a very remote area with very poor cell service and extremely cold temperatures. I couldn't even run the vehicle to stay warm. The vehicle was towed to the nearest GMC dealership where they examined the vehicle and stated that the seal of the oil filter had blown off. They further stated that the oil filter which was installed by Valvoline was the wrong size. Valvoline tested the Champion oil filter and came back with findings that the filter was the correct size and noted no damage to the filter. Either there is an unknown problem with the GM engine or the Champion oil filter. Each corporation continues to point fingers at each others product.

- Ely, MN, USA

Less than 5 minutes after my husband and 2 children parked the car and came inside, a neighbor walking rang our doorbell to let us know there was something on fire in our driveway. We ran to the back to find his truck engulfed in flames coming from the engine. We quickly called 911 and exited the house/property. The truck continued to burn with 20-25 foot flames and very black smoke for about 40 minutes until the fire department was able to control the fire. The fire was hot enough that the entire engine was significantly burnt, the seats and steering wheel were gone, the glass shattered and melted, and the tires exploded and melted. Thankfully, everyone was out of harms way and safe through this incident. However, it has been extremely traumatic on my family and neighbors and has taken a lot of time and energy to try to deal with this. The car sat in our driveway for over 2 weeks with a very potent smell causing headaches until GM and our insurance finally investigated. There is damage to our siding, driveway, landscaping, basketball hoop, trampoline, and neighbors fence. The car was only 2 years old and scares me how quickly it went up in flames and how much worse this could have been either 3 minutes earlier or if it was parked in our garage.

- Kirkwood, MO, USA

2021 GMC Sierra 1500 AT4 6.2L engine, Little over 39000 miles, Purchesed May 2021. This is the second time the vehicle has had this issue. The first time was aprox 15000 miles. I reported the issue to NHTSA-ODI on 6 Dec 2021 tracking # 11442943. I was driving down the interstate I heard a rattling coming from the engine (same as I had heard with the first issue). The check engine came on I ask On Star to do a digonsotic report (see attached report). The report indicated a Fuel Management System issue detected advised to reduce vehicle speed and pay load as possible. I was told by GM certified mechanics that this issue could cause the engine to lock up and come to a complete stop on the roadway. I fill that these vehicle are unsafe to operate under these conditions and may cause serious accidents. GM has known about these issues with these vehicles for several years and has failed to correct the problem.

- Pipestem, WV, USA

15000 miles lifter failure in traffic highway at speed 70 mph lost power engine failed multilane highway rush hour traffic no warning failure

- Plymouth , MI, USA

The contact owns a 2021 GMC Sierra 1500. The contact stated that while operating the vehicle, the dashboard gauges, instrument cluster, and infotainment center malfunctioned and became inoperable. Additionally, while starting the vehicle, there was a loud cranking sound coming from the engine compartment and the vehicle would not immediately start. The vehicle was taken to the local dealer, but the cause of the failure was not yet determined. The manufacturer was notified of the failure, but no assistance was offered. The failure mileage was 100.

- Honolulu, HI, USA

The contact owns a 2021 GMC Sierra 1500. The contact stated that while driving at an undisclosed speed, the vehicle went into Limp Mode with the check engine, DEF tank, and emission warning lights illuminated. The vehicle was taken to the dealer, and the dealer replaced several unknown sensors; however, the failure recurred. The dealer determined that the computer needed to be replaced. The vehicle was not repaired. The manufacturer was made aware of the failure. The failure mileage was approximately 35,000.

- Cartersville, GA, USA

Engine lifters failure, caused ESC light to come on and check engine light and other dash lights. Lack of power from engine causing dangerous driving in traffic.

- Fergus Falls, MN, USA

1 June 2022, while driving, started hearing a clicking noise from front end, under hood. Took to local GM dealer, Mechanic drove with me, and he heard the noise, said he would order a part and safe to drive. So, I went home. 2 June 2022 started same vehicle, a very loud banging, clicking, shuttering noise from under hood, I took back to same dealer, Dealer said collapsed valve lifter. GM service notice says for dealer to fix under warranty. Apparently, a known problem with MANY 2021 GMC 5.3 L engines. PLEASE MAKE GM RECALL THIS ISSUE FOR REPAIRDS

- Jacksonville, AR, USA

My truck shakes/shutters at random times. while steadily driving at constant speed and/ or shakes/shutters even more when I try to accelerate.

- Angelton , TX, USA

The contact owns a 2021 GMC Sierra 1500. The contact stated that the check engine warning light was illuminated and the vehicle failed to accelerate above 60 MPH. The contact took the vehicle to the dealer who diagnosed that the DEF tank had failed and needed to be replaced. The vehicle had not been repaired. The manufacturer was not made aware of the failure. The approximate failure mileage was 4,000.

- Gap, PA, USA

The contact owns a 2021 GMC Sierra 1500. The contact stated that after starting the vehicle, the check engine light remained illuminated and the vehicle would not properly accelerate while depressing the accelerator pedal. The vehicle was taken to the local dealer who diagnosed that the engine valve lifter was faulty and needed to be replaced. The vehicle was repaired. The manufacturer was notified of the failure. The approximate failure mileage was 11,000.

- Hot Springs National Park, AR, USA

While driving, when approaching speed of 40 mph, the engine begins to have dull shutter intermittently as though I am going over pot holes or rumble strips when I am not. Regardless of time or day or weather the truck has performed in this way. I have had it to the dealership twice for the issue. The first time they said they didn-??t feel anything and unable to duplicate the problem. The second time, the vehicle was with the dealer for several days trying to determine the other issue it was there for. I requested they again try to recreate the concern. The service assistance asked if I was willing to ride with the technician to see if I could point it out for him. In scheduled a time to do so, when I arrived, the technician was not there. I reside an hour away from the dealership. Making these round trips and getting no where with support or answers. When this happens, I become extremely anxious about the safety of the truck. Also- while 4 X4 is engaged, the truck has significant shutter when going up hill, as though the transmission is going to drop. The entire truck will violently shake.

- Hanoverton, OH, USA