GMC Sierra 2500 loss of power problems

Filed Sep 24, 2026 · Electrical, Engine · CA

The vehicle experienced a loss of engine power accompanied by a check engine warning light and a “Reduced Acceleration”/reduced-power condition. The exact component causing the malfunction has not yet been determined. The vehicle and any affected components are available for inspection upon request. While driving the truck uphill toward our residence, the vehicle lost significant power and had difficulty maintaining acceleration. The truck stalled several times. The sudden loss of engine power while driving on an incline created a safety risk because the vehicle was unable to maintain normal acceleration and could potentially have stopped in traffic or created a hazard for other vehicles. The problem has not yet been confirmed or reproduced by a dealer or independent service center. The vehicle has experienced the problem while being driven, including the reduced-acceleration condition and multiple stalls. The vehicle will be inspected by a GMC dealer on Monday, September 28, 2026. The check-engine warning light illuminated, and the vehicle displayed a reduced-acceleration/reduced-power condition. The truck subsequently experienced significant loss of power while traveling uphill and stalled several times. These symptoms first appeared on September 14, 15, 22, and 23, 2026.

Filed Sep 19, 2026 · Acceleration, Driver assistance · KS

While driving vehicle flashed engine power reduction signal and then the emergency brake automatic feature came on abruptly. Fortunately, I had been able to slow down after the reduced power, but if I wouldn't have quickly reacted to that, I think the emergency brake system would have caused a safety issue. Now. The vehicle is incapacitated. There were two recalls that describe this exact situation on the same year and model of truck, but my VIN number did not fall. Under that recall. The recall was for the sensor and then the second recall was because the first recall didn't correctly fix it. But the details of the faulty sensor are exactly what happened to my truck. So it sounds to me like they had more problems than just the recall that they acknowledged but they have not expanded it. My quest is to have them expand the recall to all of the vehicles that had the same problem.

Filed Jul 7, 2026 · Brakes, Electrical · AK

On XXX, I was towing my camper to Copper Center, Alaska from Palmer, Alaska when my truck experienced a full transmission shut down which put the truck into "Reduced Power Mode". We descending down the road right next to Victory Bible Camp (64741 Victory Rd, Sutton-Alpine, Ak 99674) when the exhaust break turned off and the truck decreased power and the Check Engine Light illuminated. The Diagnostic that was produced by OnStar revealed 3 different codes. ( P0700 TCM, P0747 Pressure Control Solenoid A is stuck in the "ON" position, C116b faulty brake pad wear sensor.) I called GMC of Palmer and GMC OnStar advisor, both informed me that the truck needed to be towed. My safety concerns is this.... I had minimum cell phone signal and not a gas station or service station within MILES. I was on the side of the Alaska Highway 1 which is a major thoroughfare for traffic going to and from [XXX]. Thankfully there were a few kind folks that pulled over to offer assistance. My truck is a 2023 GMC Sierra 2500hd with only 26,262 Miles on it. I purchased this vehicle XXX. (It Still has the Temporary Tags on it.) If had been in a different part of Alaska when this transmission failed to function properly then we could be talking about a life or death situation. Especially, if my child was with me. I was hauling my camper that weighed ATMOST, 7,000 pounds. This is less than 40% of the trucks ability. I feel that this could put someone into a dire situation had they not had the experience with emergency situations like I have had. (Prior Military Service). I have also filed a complaint with GMC Motors. Case# XXX. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Jun 30, 2026 · Engine · 100,000 miles · LA

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.

Filed Mar 24, 2026 · Transmission · NH

While driving on the highway at normal speed, my vehicle was operating completely normally with no warning lights, messages, or prior issues. Without any warning, the vehicle suddenly lost the ability to accelerate and felt as if it had been shifted into neutral. I immediately had to pull over to the side of the highway, as this created a dangerous situation with surrounding traffic. The vehicle had to be towed to a mechanic. Upon inspection, I was informed that a coolant line connected to the transmission had completely blew off, causing a rapid loss of transmission fluid and resulting in total transmission failure. I was told this was not due to a rusted or deteriorated clamp, but rather a sudden component failure. This vehicle has been meticulously maintained and I have owned it for less than one year. There were no prior symptoms, leaks, or warning signs leading up to this incident. This appears to be a sudden and unexpected mechanical failure, not caused by neglect or misuse. The loss of power while driving at highway speed posed a serious safety risk to myself and others on the road.

Filed Feb 28, 2026 · Transmission · LA

Was driving down the highway and was approaching a red light. As I was slowing down my transmission down shifted hard and my rear wheels briefly locked up and my truck went in to reduced power Took to dealership only to find out the valve body failed and my truck wasn't covered

Filed Jan 24, 2026 · Transmission · PA

Driving at approximately 30-35MPH merging in traffic, the transmission shuttered and went into reduced power mode. ECM reported a 747 code and valve body failure.

Filed Jan 12, 2026 · Transmission · MO

Summary of Issue On [XXX], my family and I departed Kansas City, Missouri, for a camping trip to Great Smoky Mountains National Park (Cades Cove), Tennessee, approximately 800 miles away. We were towing a 2020 Forest River Salem FSX/RTX travel trailer, estimated at approximately 6,000 pounds loaded, using a Reese weight distribution hitch with integrated sway control. This load was well below the rated towing capacity of the vehicle. On [XXX], while driving without the trailer attached, the vehicle displayed multiple warnings including “Reduced Engine Power” and a transmission system alert. I immediately pulled over, shut the vehicle off, and restarted it. The warnings persisted. I cautiously drove approximately five miles to Twin City GMC, where the vehicle was diagnosed with a failed transmission valve body. Dealer and Manufacturer Response The service manager at Twin City GMC informed me that the required valve body was on national backorder, with multiple vehicles ahead of mine, and that wait times had reached up to three months. To confirm, I contacted Molle Chevrolet (Blue Springs, MO) and Randy Curnow GMC (Kansas City, KS). Both dealerships independently confirmed that this was a known and recurring issue, and that extended backorders for the valve body were common. I was informed that GMC could provide a daily rental allowance, but the rental vehicle would not permit towing. With my family, three dogs, and travel trailer stranded 800 miles from home, this option was not viable. As a result, I was effectively forced to trade in my truck and purchase a replacement vehicle to safely return home. Manufacturer Awareness and Complaint History GMC has demonstrated awareness of this issue through service bulletins, widespread owner reports, and media documentation addressing transmission valve body failures and parts shortages. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Dec 8, 2025 · Transmission · MI

Pulling into a driveway and the truck made a loud clunk and the check engine light, traction control light, and a reduced engine power light came on and the truck came to an abrupt stop. When the gear shift was put into reverse or any forward gear the truck would rev up without touching the gas pedal. The left rear wheel locked up. After paying over $700 in tow bills to get the truck towed to our house and then to the dealer we were told that the transmission had a catastrophic internal failure. This truck only has 82,000 miles on it and is a 2021!

Filed Oct 23, 2025 · Fuel system · 143,000 miles · MI

The contact owns a 2019 GMC Sierra 2500. The contact stated that while her husband was driving 30 MPH and depressing the accelerator pedal, there was an abnormal sound coming from the front of the vehicle, and the vehicle lost power unexpectedly. The contact stated that her husband was able to pull over to the right side of the road while waiting for tow truck assistance. The vehicle was towed to the residence. The vehicle was not towed an independent mechanic or dealer to be diagnosed. The engine was replaced, and the vehicle was repaired. The contact related the failure to the federal safety agency Campaign Number: 23V047000 (FUEL SYSTEM, DIESEL); however, the VIN was not included in the recall. The manufacturer was not notified of the failure. The failure mileage was 143,000.