Dtc code P1098 present related to faulty coolant control valve on 3.0 duramax diesel engiine. This is a known issue with this engine and is supposed to be covered under the 100K mile powertrain warranty. Previously took vehicle into dealership for repair involving replacement of the coolant control valve but was told reprogramming of the ECM was required first step per GM repair bulletin. Reprogramming cost me $195 and was told this was not covered under the 100K powertrain warranty. Now, a few months later, the same issue and dtc code P1098 happened again while driving on freeway at freeway speeds and caused vehicle computer to limit speed of the vehicle which caused hazardous situation in construction zone as was not able to maintain speed of traffic while towing trailer with boat. I also understand that GM has issued special extended warranty related to this coolant control valve in September 2025 which extends the warranty coverage up to 15 years and/or up to 150K miles but I was told at the dealership that my VIN# does not qualify for this extended coverage for some unknown reason?

- Waterford, MI, USA

Transmission on my vehicle has failed three times since I bought the vehicle in October of 2021. Vehicle currently has 39,000 miles. First transmission issue was resolved by the dealership by replacing the transmission valve body. This solved the problem for approximately 12,000 miles. In September of 2025 with 39,000 miles the transmission suffered a catastrophic breakdown which lead to complete transmission replacement. After being -??fix-?? the vehicle suffered another catastrophic transmission failure within 400 miles of the complete transmission replacement. This incident caused the vehicle to shut completely down and I was stuck in the traffic lane of the US Highway. Fortunately my vehicle and I were not struck while waiting 30 minutes for a tow truck. Presently the vehicle is back at the dealership awaiting repair. From my review of available on-line information it appears there are 10-??-??s of thousands of GMC Sierra pickups with major transmission issues. This needed to be addressed before someone is killed due to the poor quality of these GMC trucks.

- Mountain Iron, MN, USA

The contact owns a 2021 GMC Sierra 1500. The contact stated that while driving 45-50 MPH, the engine revved and the transmission unintendedly downshifted, causing the vehicle to decelerate unexpectedly. The transmission then seized, and the vehicle skidded. No warning light was illuminated. The vehicle was towed to the dealer, who determined that the transmission had failed and needed to be replaced. The vehicle was not repaired. The manufacturer was not made aware of the failure. The failure mileage was approximately 127,000.

- Rathdrum, ID, USA

The contact owns a 2021 GMC Sierra 1500. The contact received notification of NHTSA Campaign number: 24V797000 (POWER TRAIN), and the dealer performed an interim repair on the vehicle. In March 2025 the part was available, and the recall repair was completed. The contact stated that on one occasion, while driving at an undisclosed speed and then coming to a complete stop, the vehicle jerked and the transmission unexpectedly downshifted. The message -??Low Power Mode-?? was displayed on the instrument panel. The vehicle then failed to accelerate as intended while depressing the accelerator pedal. The contact drove to a parking lot and turned off the vehicle. The vehicle was towed to Don Moore Chevrolet GMC, where it was diagnosed with transmission control valve failure. The contact was informed it would be months before the repair could be performed. The vehicle was towed to another dealer, where the transmission control valve failure was confirmed, and the contact was informed there were metal shavings found inside the transmission. The vehicle remained at the dealer unrepaired. The manufacturer was made aware of the failure. The failure mileage was approximately 115,000.

- Owensboro, KY, USA

Constant engine issues, cams, lifters. Transmission problems. These engines in these vehicles need to be RECALLED. I have bought 6 of these trucks and all of them have the same issues. SPENDING 14k on new engines one after another is ridiculous. These are classified as -??work-?? trucks and can-??t handle -??working-???

- Winchester , VA, USA

Transmission failure at a little over 120,000 miles while towing a side by side on the highway. This highway has a speed limit of 80 which is dangerous when the vehicle stops working properly for myself and any other drivers in itself. Earlier this year the transmission had been updated due to a recall and was deemed to work good by the dealership but didn-??t notice any difference. Had an engine light pop up a couple hours before but no messages or any other signs to inform me of the issue and was still working fine with no struggle until it gave out

- Ada, OK, USA

Torque Converter failure confirmed by dealer: was driving at high way speeds when I noticed a slipping sensation from the transmission upon any sort of acceleration. No warning lights were illuminated or any symptoms leading up to the failure. This could have potentially caused me to lose any form of acceleration that would enable me to get off of the highway or away from a situation requiring sudden acceleration.

- Salado, TX, USA

I have contacted local GMC repair facility (Frank Brown in Lubbock Tx.) about the safety recall on my 6.2 liter engine to attempt to schedule an inspection of my engine and cannot get them to inspect the engine which the recall notice said they would do. They continue to stall and say the inspection isn't approved by GM. I've tried 3 different times to address this isuue without satisfactory results. I recieved the GM safety recall N252494000 notice for my vehicle in May 2025

- Lubbock, TX, USA

The contact owns a 2021 GMC Sierra 1500. The contact stated that while driving 15 MPH, the vehicle briefly jerked and jolted, prompting him to discontinue driving the vehicle. The vehicle returned to normal functionality, but the failure became a regular occurrence. The check engine warning light was illuminated. The vehicle was taken to the dealer, who diagnosed failures with the output shaft speed sensor and the transmission control module. The vehicle was not repaired. The manufacturer was notified of the failure but provided no assistance. The failure mileage was 89,000.

- Huntingdon Valley, PA, USA

Have owned my 2021 GMC Sierra 1500 with the 3.0 Duramax for a year and the check engine light has come on multiple times for a "Coolant Control Valve" issue. The truck runs the fans at 100% and puts the truck into reduced power at least once a day. I have read that GM sometimes will not cover this repair under powertrain warranty even though it's an engine problem. Please fix this issue! To answer the previous questions, the coolant control valve is malfunctioning, and the truck is currently at the dealer being inspected. Yes the dealer has said this issue is common on these trucks (confirmed by National GMC in American Fork, Utah). Yes the check engine light has appeared multiple times. These issues started appearing in June 2025

- Alpine, UT, USA

This vehicle experienced catastrophic engine failure while I was on vacation 400 miles from home. I have researched this failure and there is a class action lawsuit against GMC. My truck has been at the dealer for 25 days and still waiting for authorization from Fidelity Warranty Services. Considering it-??s such a common problem I feel GMC should be paying for this. At the very least the warranty company is aware of this problem and purposely delaying the authorization to repair. I just bought a new camper which I cannot use. I am fisherman and cannot use my boat. My beach pass is also on the vehicle. So essentially my summer has been ruined by a company that produced a faulty vehicle and didn-??t discord this information to me.

- Fall River, MA, USA

What component or system failed or malfunctioned, and is it available for inspection upon request" The Coolant Control Valve has stopped working. How was your safety or the safety of others put at risk? While driving the truck can overheat very quickly which can lead to dangerous temperatures as well as cause me to make an emergency stop on the highway to allow the truck to cool down. Has the problem been reproduced or confirmed by a dealer or independent service center? Yes, I have discussed with a dealership in person and independent mechanic who have confirmed the issue and confirmed it is a very common issue. So common that the only replacement part for the problem is backordered. Has the vehicle or component been inspected by the manufacturer, police, insurance representatives or others? No, they confirmed the issue without inspecting the vehicle because of how common it happens. Were there any warning lamps, messages or other symptoms of the problem prior to the failure, and when did they first appear" There were no warnings before the issue. The issue happened and then the check engine light turned on as well as a "reduced engine power" message.

- Layton, UT, USA

I own a 2021 GMC Denali with a 6.2L V8 L87 engine and 45,500 miles. I have confirmed the presence of metal shavings in the oil and oil filter, indicating that the engine is beginning to fail. When I took the vehicle to my local dealership, I was informed that there is currently no fix for this issue and was advised to continue driving the vehicle. This poses a serious safety risk-?"not just to me and my family but also to others on the road. A sudden loss of power could lead to a dangerous accident, and I do not want to be responsible for something preventable that could harm innocent people. My concern is that GM is aware of this engine issue but has instructed me to keep driving the vehicle, despite the known defect. How can GM be allowed to avoid accountability for such a critical safety matter" If a fatal accident were to occur, would the responsibility fall on GM or the NHTSA for failing to act" It-??s also troubling that GM continues to profit by selling new vehicles, including the 2025 models, with similar issues, all while neglecting to provide solutions for affected customers like me. I purchased this $80,000 truck in good faith, but now no dealer wants to trade or buy these trucks without me taking a significant financial loss-?"something GM should be responsible for. As a taxpayer, I find it unacceptable that we bailed out GM in the mid-2000s, yet they continue to disregard accountability for their actions. I urge the NHTSA to take this issue seriously. A specific deadline should be set for GM to resolve this issue, and they should face daily penalties for every day they fail to provide a fix. If no resolution is possible, full refunds should be mandated. Please address this issue promptly, as it affects real people-??s safety and financial well-being every day.

- Debary, FL, USA

At around 60,000 miles I had experienced shuttering and jerking in low gears and the vehicle shoots forward when coming to a complete stop. I was able to take the vehicle in a short time after and I was told by the dealership that it needed a transmission flush. I completed the flush and after a week or two it started doing it again. I took it to a transmission shop and they advised it is the transmission valve body that is bad. I believe this started happening before my warranty was out but due to me bringing it in after the mileage they would not honor the warranty. This could cause multiple hazards at stops and while driving. No warning lamps or message have ever appeared.

- Mcalester, OK, USA

The check engine light came on at one point. I took it to figure out why the check engine light was coming on and the scanner indicated that the NOX catalyst was below threshold. I researched it and it is a common issue. The check engine light eventually turned off after a couple of days. About 2 weeks later it came back on. I noticed as i was driving the coolant fans were running at 100% meaning that they were blowing long and hard. So I scanned it and it said that the engine coolant valve was at fault. This is also a common issue with the vehicle, particularly in the 2021 GMC Sierra 1500 3.0 Turbo Diesel. It is a faulty part and it costs thousands of dollars to replace. How can these two issues not be on a national recall by GM? They are too common and very expensive to repair. This issue is so common that now the valve is on a national back order. Meaning the parts may not be available for 30-120 days. The vehicle is not safe to drive with a bad engine coolant valve. I have now a rental car for the past 7 days while my truck sits waiting for a valve to arrive and pay thousands in repair just to drive it again.

- Jacksonville, FL, USA

wn a 2021 GMC Sierra 1500 6.2L (VIN: [XXX] ), which is now experiencing a severe misfire, engine ticking, and diagnostic code P318A. I-??ve confirmed this issue is related to GM Recall N252494001 for engine connecting rod/crankshaft failure. However, I-??ve been told my VIN has not yet been activated for recall repairs, and both the local dealership and GMC support have refused to escalate my case or offer assistance. This is a known safety issue, and I-??m now at risk of total engine failure and significant financial loss while waiting for GM to act. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

- Somerset, KY, USA

What component or system failed or malfunctioned, and is it available for inspection upon request" The valvetrain system failed due to broken rocker arms, which resulted in additional internal engine damage. This failure occurred under normal driving conditions. The affected components have not yet been discarded and are available for inspection upon request.How was your safety or the safety of others put at risk? The failure caused sudden engine misfiring and knocking, reducing engine power while I was operating the vehicle. This significantly compromised acceleration and response time, especially during merging and lane changes, which could have led to an accident. Any unexpected loss of power or engine instability at highway speeds poses a serious risk to myself, passengers, and other motorists.Has the problem been reproduced or confirmed by a dealer or independent service center? Yes. The issue has been diagnosed and confirmed by an independent certified mechanic, who verified the broken rocker arms and resulting engine damage during inspection.Has the vehicle or component been inspected by the manufacturer, police, insurance representatives, or others? The vehicle has not yet been inspected by the manufacturer, police, or insurance representatives. Only a certified independent mechanic has inspected the failure thus far.Were there any warning lamps, messages, or other symptoms of the problem prior to the failure, and when did they first appear" Yes. The check engine light appeared and the engine began running rough and producing a knocking sound. These symptoms occurred just prior to the confirmed failure and prompted me to stop driving the vehicle immediately and have it inspected. Given the seriousness of this issue and reports from other GMC 5.3L engine owners experiencing similar rocker arm failures, I urge the NHTSA to investigate this potential defect. It poses a real and significant safety risk.

- Buford, GA, USA

The coolant control valve is faulty and is on national backorder causing months of my truck sitting in the shop. This is not an isolated issue. GM is claiming it is not covered under warranty, but the part design is clearly a serious issue.

- St. George, UT, USA

The contact owns a 2021 GMC Sierra 1500. The contact stated while driving 75 MPH, the vehicle jerked and downshifted to overdrive. The message "Engine Power Reduced" was displayed on the instrument panel. The driver depressed the accelerator pedal, but the vehicle failed to exceed 4 MPH. The vehicle was taken to the dealer, where it was diagnosed that the valve body failed, which caused the transmission to fail. The vehicle was repaired. While the contact was driving home after the vehicle was picked up, the vehicle jerked and hesitated. The dealer was contacted and informed the contact that if the check engine warning light becomes illuminated the vehicle could be diagnosed. After several days, the check engine warning light illuminated, and the vehicle was taken to the dealer where it was diagnosed that the shutter valve had failed and needed to be replaced. The vehicle was repaired. The contact stated that the failure persisted. The contact received NHTSA Campaign Number: 24V797000 (POWER TRAIN). The vehicle was repaired; however, the failure persisted. The manufacturer was made aware of the failure and offered the contact assistance with the transmission repair. The failure mileage was approximately 119,000.

- Saint Michaels, AZ, USA

My 2021 GMC Sierra 1500 Diesel Truck is displaying the Check Engine Light which I was told by the local Mount Vernon GMC Dealership is a failed Temperature Control Valve affecting the transmission. I also get a warning message of "Reduced Engine Power". I am told that it is OK to drive the vehicle but at reduced power. The dealership told me they ordered a replacement part which is covered under warranty on May 7, 2025, but showed on "Back Order". Every time I call to follow up on the status, I'm told it is still on "Back Order", and they cannot do anything to improve the delivery. Why does a customer, owning a "Denali" truck under warranty, can't get the problem resolved" I have a recall notice from GMC dated January 2025 about this very problem and have shown it to GMC dealerships during regular services, and still have the problem. Since I have bought this truck, I have experienced a failed right running board that cost $1,500 to repair a few months ago which is failing again. The driver side mirror now vibrates when I put the truck into drive after being in reverse, and I cannot get any idea on when this transmission valve problem will be fixed which is causing me serious delays in using the truck to pull a trailer. Prior to this problem I had the dealership replace my brakes which required 2 follow-up repairs due to the "GMC original rotors" being warped that required machining to make them not vibrate which to me, now makes them "used". This means I paid full price for "repaired" parts! I thought that by buying a GMC "Denali" 1500 Sierra truck I was buying the "top of the line" in pick-up trucks but now finding out it's a lemon. I love the truck, but not the problems. What do I need to do to get this fixed" [XXX] [XXX] INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

- Mount Vernon, OH, USA