208 of the
2,284 complaints filed about the GMC Sierra 2500
are about the engine —
9% of everything owners reported.
The worst model year for it is 2001.
On 07/10/2026 at approximately 1:10 a.m., the parked and unoccupied vehicle caught fire while turned off. The vehicle had not been driven for several hours. A neighbor was awakened by the horn/alarm and popping noises, observed fire near the passenger-side cab/engine area, and called 911. The fire rapidly spread throughout the cab, engine compartment, rocker-panel areas, wheel wells, and truck bed, creating an explosion hazard and threatening a nearby occupied residence and garage. The fire department extinguished the blaze, but the vehicle was completely destroyed. Before the fire, the vehicle had experienced recurring coolant warnings, a DEF-system warning, and delayed starting associated with the main battery. No smoke, fuel odor, intentional ignition source, charging device, or known external fire source was present before the incident. Weather was calm. The exact failed component and cause remain UNKNOWN. A firefighter stated that the apparent fire origin was near the passenger side of the vehicle. The remains are available for inspection, subject to coordination with the vehicle owner and insurer. The incident has been reported to the fire department, insurer, manufacturer, and NHTSA.
NHTSA complaint #11752275 — an unverified report by a vehicle owner.
The contact owns a 2020 GMC Sierra 2500. The contact stated that the check engine warning light was illuminated, and the message "Reduced Power" was displayed. The vehicle was taken to the dealer, where the turbo actuator and wastegate position sensor A-circuit were replaced; however, the failure persisted. The vehicle was taken back to the dealer, and the contact was advised that another diagnostic test was needed. The contact declined to pay for the diagnostic test. The vehicle was taken to a retired GM mechanic, who diagnosed the vehicle with turbo charger failure. The vehicle was not repaired due to the cost. The manufacturer was notified of the failure, but no assistance was provided. The failure mileage was approximately 100,000.
NHTSA complaint #11747347 — an unverified report by a vehicle owner.
I am reporting repeated failures involving both the transmission and diesel emissions (DEF) system on my 2021 GMC Sierra 2500HD Denali equipped with the 6.6L Duramax diesel engine and Allison 10-speed automatic transmission. While under warranty, the truck required replacement of the aftertreatment fuel injector and later the Reductant Control Module due to DEF/emissions system failures. General Motors also completed recall-related transmission software updates on the vehicle. At approximately 154,833 miles, the transmission began shifting improperly, set transmission fault codes, and required complete replacement at my expense. Less than 5,000 miles later, the vehicle again experienced a "Service DEF System" warning with multiple diagnostic trouble codes. Repairs required replacement of the DEF tank, DEF heater assembly, and NOx sensor. These repeated failures involve major drivetrain and emissions components on a heavy-duty truck. DEF system failures can place the vehicle into reduced-power (derate) mode, limiting vehicle performance and creating potential safety concerns while driving or towing. I am submitting this complaint so these failures can be documented as part of NHTSA's evaluation of similar vehicles.
NHTSA complaint #11746749 — an unverified report by a vehicle owner.
I recently purchased my vehicle from Big Star Dealership in Baytown Tx. At a little over 1000 miles i was towing a camper. The vehicle stalled, fuel pouring from engine. It was towed and repaired due to fuel pump failure. At a little over 3000 miles the vehicle would not start. Dealership initially said water contamination then changed it and said gasoline contamination and now they say DEF contamination. The vehicle stalling the first time almost caused me to wreck the vehicle
NHTSA complaint #11737988 — an unverified report by a vehicle owner.
GM Duramax L5P diesel engine electrical connector for #4 fuel injector. This failure caused the Diesel exhaust brake, which controls downhill speed, to disengage, extreme shaking of the vehicle, emissions system warning and speed limiting. This occurred while descending a steep grade while towing a 34 feet long, 10,000 pound trailer. This is a known issue with this diesel engine and documented in GM Technical Service Bulletin 23-NA-027. Inspection and repair at a GM dealership confirmed a known issue with the #4 injector pigtail connector caused by improper wire routing and interference wit the Sound Shield and Valve Cover Heat Shield This was a sudden failure of the #4 pigtail connector with no advance warning. In addition to violent shaking of the vehicle, multiple warnings on the DIC indicating that the Diesel Brake was disengaged, the emission system had an issue, and speed would be limited.
NHTSA complaint #11736800 — an unverified report by a vehicle owner.
The contact owns a 2024 GMC Sierra 2500. The contact stated while reversing, the rear-view camera displayed a blank screen. The 4WD system engaged unintendedly, and the park assist sensor was inoperable while an unknown message was displayed. Additionally, the vehicle lost motive power while driving. The check engine warning light was illuminated. The vehicle was towed to the dealer, who replaced an unknown module and reset the computer, but the failure persisted. The contact stated that the vehicle was taken to the dealer five times, but the failure recurred after several unknown repairs. The vehicle was not repaired. The contact had requested for a buyback from the dealer, but no assistance was provided. The manufacturer was made aware of the failure. The failure mileage was approximately 8,000.
NHTSA complaint #11730404 — an unverified report by a vehicle owner.
The contact owns a 2021 GMC Sierra 2500. The contact stated that while driving at 55 MPH, the vehicle stalled unexpectedly. There were no warning lights illuminated. The vehicle was taken to the local dealer, where it was diagnosed, and determined that the engine needed to be replaced. The engine was replaced; however, the failure recurred. While at a stop and attempting to drive around a curve, the vehicle stalled. No warning lights were illuminated. The vehicle was taken to the local dealer, where it was diagnosed with engine failure. The vehicle was not repaired. The failure mileage was approximately 77,000. The VIN was not available.
NHTSA complaint #11728457 — an unverified report by a vehicle owner.
Oil cooler blew and mixed oil in coolant reservoir. Possibly causes overheating and engine seizure. This has been confirmed with a certified GM service center. The service center inspected fixed it then within 5 miles had to be returned to the dealer because it happened again.
NHTSA complaint #11724478 — an unverified report by a vehicle owner.
The contact owns a 2017 GMC Sierra 2500 Denali. The contact stated that while driving at an undisclosed speed, the check engine warning light illuminated. The vehicle was taken to the dealer, where it was diagnosed with a failure of the #8 glow plug. The contact was informed that all eight glow plugs were replaced. The vehicle was repaired. The contact stated that the failure was a known failure with the vehicle. The manufacturer was made aware of the failure, and a case was filed. The failure mileage was approximately 63,800.
NHTSA complaint #11721718 — an unverified report by a vehicle owner.
Component / System Failure The exhaust system, specifically the exhaust manifolds and previously the EGR system components, appear to have failed or malfunctioned, allowing exhaust gases to enter the passenger cabin. The dealer initially replaced the EGR cooler diverter on December 23, 2025. However, the condition persisted. On February 3, 2026, cracked exhaust manifolds were identified by the dealership, and a major front-end teardown was advised to complete the repair. The vehicle is currently available for inspection upon request. ⸻ How Safety Was Put at Risk The malfunction allowed exhaust gases, including carbon monoxide, to enter the passenger cabin during vehicle operation. Carbon monoxide readings inside the cabin reached up to 50 parts per million (ppm) while driving. Carbon monoxide is a toxic gas that can cause: •Headaches •Dizziness •Impaired concentration •Nausea •Vision disturbances Because carbon monoxide is odorless and colorless, this presents a significant safety risk, particularly at highway speeds where driver alertness is critical. The exposure occurred while operating the vehicle in normal driving conditions. This created a potential risk of driver impairment and increased risk of collision. ⸻ Has the Problem Been Reproduced or Confirmed? Yes. The vehicle was presented to the dealership three times for the same exhaust intrusion concern: •December 16, 2025 •December 29, 2025 •February 3, 2026 During the February 3 visit, the dealership confirmed cracked exhaust manifolds requiring major disassembly for repair. The carbon monoxide readings were observed during vehicle operation. The exhaust odor and intrusion symptoms were consistently present following the first attempted repair. ⸻ Has the Vehicle Been Inspected by Manufacturer or Others? The vehicle has been inspected by the authorized dealership on multiple occasions. Two manufacturer customer care cases were opened.
NHTSA complaint #11717926 — an unverified report by a vehicle owner.
The contact owns a 2022 GMC Sierra 2500. The contact stated that the engine was making an abnormal rattling sound on cold starts. There was no warning light illuminated. The vehicle was taken to the dealer, where the front muffler exhaust baffle was replaced; however, the failure persisted. The vehicle was taken back to the dealer, where the contact was informed that the rattling sound could not be heard; however, the contact stated that the rattling sound had become louder, and other individuals were able to hear the rattling sound. The vehicle was not repaired. The manufacturer was not notified of the failure. The failure mileage was unknown.
NHTSA complaint #11717562 — an unverified report by a vehicle owner.
I own a 2024 GMC Sierra Denali Ultimate 2500HD diesel that has been out of service for 52 days due to an oil cooler / service bulletin related failure. The vehicle is under warranty. The required replacement part is on national backorder and, as of today, has not shipped. The current estimated ship date is February 17. During this time, neither the dealership nor GMC has provided proactive communication. I have had to repeatedly contact them for updates. This extended inability to repair a critical component, combined with the lack of parts availability and communication, raises concerns about the reliability of this system and the manufacturer’s ability to support safe operation of the vehicle in a reasonable timeframe. The truck is my primary vehicle and is intended for towing and transportation. Being unable to repair it for nearly two months due to parts unavailability presents a significant safety and reliability concern.
NHTSA complaint #11717560 — an unverified report by a vehicle owner.
Burning an unusual amount of oil. Have seen several instances of blue smoke in the exhaust. Have had to add over a quart of oil twice in less than 6500 miles.
NHTSA complaint #11714116 — an unverified report by a vehicle owner.
Complete engine failure with no warning on major road in heavy traffic. Very dangerous situation to pull off safely. Vehicle was towed to dealer and confirmed engine is seized. Unknown cause at this time. Transmission has had valve body replaced prior to engine failure. Transmission still has shudder after valve body replacement and prior to engine failure.
NHTSA complaint #11709276 — an unverified report by a vehicle owner.
Constantly having to clean the map Senor to be able to drive pickup without service emissions alerting me to clean the map Senor or my truck goes in limp mode. This can’t be normal to have to clean this so much. My truck is fairly new and should not be having these issues. Put a scanner on my GMC and the code says P122D. I got on YouTube and I found MANY people complaining about my exact problem for quite some time!
NHTSA complaint #11707394 — an unverified report by a vehicle owner.
The contact owns a 2024 GMC Sierra 2500. The contact stated that the vehicle was idling roughly, and the RPM fluctuated between 500 and 1,000 RPM while idling. The check engine warning light was illuminated. Additionally, the contact stated that the fuel economy had decreased to 13 miles per gallon. The contact stated that upon scanning the vehicle, the contact retrieved DTC: P0606 and P062B. The contact related the failure to GM Campaign Number: N232415860 (Fuel Injector Flow Rate Compensation). The dealer was contacted and informed the contact that a fee would be charged for a diagnostic test. The vehicle was not diagnosed or repaired. The manufacturer was notified of the failure and referred the contact to the NHTSA Hotline for assistance. The failure mileage was approximately 70,000.
NHTSA complaint #11696287 — an unverified report by a vehicle owner.
We were towing a fifth wheel camper with our truck on an interstate highway in Pennsylvania when our serpentine belt burst suddenly and without warning. Our truck is a 2025 model with only 10,000 miles driven. We lost all power steering and power brakes of both the truck and the camper and the motor shut off while we were driving at 65 mph. My husband struggled to gain control of the truck and camper which was severely fishtailing and was eventually able to get over to the shoulder and stop the vehicles. We were towed to a GMC dealership where a factory technician happened to be on site providing an in-service for the dealership's service team. He inspected our truck and we were told that he said that GMC is aware of catastrophic failures in these serpentine belts. We were also told that he took photos and was sending a report to the GMC factory regarding our situation. When the serpentine belt blew, it damaged fan blades, shroud, oxygen sensors and our air conditioner belt (which fell off 200 miles later). We had absolutely no warning of the sudden catastrophic failure of the serpentine belt and came close to losing our lives. Our biggest concern is that the serpentine belt was replaced with the exact same model of belt that failed. What does it take for a company to recall a known defective belt? A fatality? We were very fortunate to have walked away without injury or losing our lives. We have written a letter to GMC but they have not contacted us as of yet.
NHTSA complaint #11691951 — an unverified report by a vehicle owner.