2023 GMC Sierra 1500 Powertrain (other) Problems

My truck threw the code p0747 for fail valve body. When I do my research its a common problem. GM is stating my truck isnt covered.

NHTSA ID

11755890

Incident

Jul 31, 2026

While towing my trailer the vehicle intermittently slams gears and will hesitate the back tires momentarily to the point of screeching. This has led to close calls being nearly rear ended and having to pull over. This started out as a hard slam while trailering on the highway and has progressively gotten worse. Had into dealership twice to multiple times to try and figure out the issue but it’s not throwing any codes and they can’t get it to duplicate the issues. Nothing can be replaced due to no codes even though they think the valve body is going bad. Leaving the vehicle as a ticking time bomb for failure which could result potentially in a catastrophic incident. Only had the vehicle for one year now has 37k miles on it and have had the ecm, full wiring harness, and multiple sensors replaced already for a different problem early this year that had the truck in the shop for a month.

NHTSA ID

11752774

Incident

Jul 12, 2026

Engine light came on while driving and a message on dashboard said Service Transmission Now.Unable To Shift Soon. Took to dealer and they said it was the park position switch 1circuit high. Had to order part but not knowing how long to get it. Truck only has 12468 miles. Luckily I got it to the dealer ASAP. IF I were on the highway or a remote road, I feel that a serious accident would have happened. Having an electronic controlled console shifter not being able to get the truck to shift gears to slow down or stop is a real safety issue. Extended warranty does not cover anything like this. Please look into this. Thank you

NHTSA ID

11752068

Incident

Jul 16, 2026

I was driving my family on the highway and my truck completely shut down. The screen flashed a warning and it slowly started decelerating. Thankfully I was able to make it to the shoulder of the road safely. Engine failure was a known safety issue with my model of truck, but I completed the L87 Engine Loss of Propulsion safety recall testing on 9/18/2025 and was assured my engine passed the testing and was not at risk for engine failure.

NHTSA ID

11748693

Incident

May 24, 2026

While traveling at highway speed during rush hour commute, the vehicle lost engine power and stalled. While coasting, I tried to restart the engine several times without success. Before coming to a stop, I attempted to get to the shoulder safely. Unfortunately, a portion of the vehicle was left partially in the lane and on the shoulder. Once I was completely stopped, I tried to put the electronic shift control into neutral so I could push the vehicle safely to the shoulder. The shifter would not allow me to shift into neutral and other override methods researched failed to work. I continued to try and restart the vehicle without success. I was in an unsafe position during rush hour commute for about 50 minutes until roadside assistance arrived and loaded and towed the vehicle. There was no warning of the issue prior to the incident. A code (P129F-Fuel Pump Driver Control Module Speed Signal Incorrect) was produced after the stall occurred via my GMC app. My vehicle was towed to my local dealership for service, but have not received the vehicle back at the time of reporting.

NHTSA ID

11746738

Incident

Jun 25, 2026

[XXX] [XXX] Phone: [XXX] Vehicle Information: Year: 2023 Make: GMC Model: Sierra Denali Ultimate Engine: 6.2L V8 VIN: [XXX]: Mileage: Approximately 52,000 miles BACKGROUND: I previously had the engine serviced under a GM recall campaign related to known 6.2L V8 engine concerns. Despite that repair, the vehicle has since experienced two separate highway-speed loss-of-propulsion events. COMPLAINT The vehicle suddenly lost power while being driven at highway speed. No warning lights, check-engine lights, reduced-engine-power messages, or transmission warnings appeared. In both incidents, I was forced to coast to the shoulder of the roadway. The vehicle would not resume normal operation until it was stopped and restarted. This condition has now occurred twice. SAFETY CONCERN The sudden loss of propulsion during highway operation creates an immediate safety hazard and increases the risk of collision due to the inability to maintain speed with surrounding traffic. REQUESTED NHTSA ACTION 1. Record this complaint as a repeat loss-of-propulsion event. 2. Evaluate whether similar complaints exist involving 2023 GMC Sierra Denali Ultimate vehicles equipped with the 6.2L V8. 3. Consider this complaint in any current or future investigations involving loss of propulsion, stalling, engine failure, or powertrain concerns. 4. Review whether vehicles previously repaired under GM recall campaigns continue to experience similar failures. [XXX]: Update – Vehicle Disabled and Awaiting Engine Replacement Since filing my initial concerns regarding repeated loss-of-propulsion events, the condition of my vehicle has significantly worsened. During the dealership's inspection and test drive, the engine reportedly failed and locked up. The vehicle could not be restarted and required further diagnostics. On June 20, 2026, I received a text message from the dealership that the required engine parts remain on backorder INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA ID

11745455

Incident

May 18, 2026

the vehicle is actively presenting severe mechanical symptoms that make it entirely unsafe to operate on public roads. Specifically, it exhibits a violent shuddering and vibration through the cabin when coasting or cruising at highway speeds. Furthermore, it undergoes aggressive jerking, harsh engagement, and dangerous hesitation the moment I press the gas pedal to accelerate or merge.

NHTSA ID

11742955

Incident

Jun 8, 2026

The transmission control module failed. The dealer said a I a high voltage alarm signal code. This was the diagnostic inform received from the dealership service department. Primary]: MDIAG : MISC. VEHICLE DIAGNOSIS. CHECK ENGINE LIGHT ILLUMINATED AND GETTING MESSAGE FOR SERVICE TRANSMISSION, UNABLE TO SHIFT. PLEASE CHECK AND ADVISE * Repair items per diagnosis: FOUND P07B4 STORED IN SYSTEM. VERIFIED WIRING OK TO GEAR SHIFT CONTROL MODULE. SI STATES IF WIRING GOOD TO REPLACE GEAR SHIFT CONTROL MODULE AND IF CODE RESETS TO REPLACE ECM. RECOMMEND STARTING BY REPLACING GEAR SHIFT CONTROL MODULE The truck would not shift or go into gear at all. This was concerning because the transmission could have stopped shifting while I was driving myself and my children around. This warning light came on while I was driving on the highway. My vehicle has about 58,000 miles on it and is still under powertrain warranty. But the dealership is saying this repair isn’t included.

NHTSA ID

11742551

Incident

May 19, 2026

The truck side toy down shift and the accelerator was very high…. When I was going to park the reverse was not shifting…

NHTSA ID

11741918

Incident

May 28, 2026

Upon accelerating on the freeway, rear wheels locked up completely almost causing me to hit multiple vehicles. Was repeatable and was able to record the event. Manufacturer claims unable to reproduce and bring back if it happens again. No lights were set.

NHTSA ID

11741318

Incident

May 23, 2026

Model: Sierra Denali Ultimate Engine: 6.2L V8 VIN: [XXX] Mileage at Most Recent Incident: Approximately 52,000 miles Safety Complaint Summary I am submitting this complaint to report a recurring loss-of-propulsion and engine power event involving my 2023 GMC Sierra Denali Ultimate equipped with the 6.2L V8 engine. This vehicle has experienced two separate incidents in which it suddenly lost power while being operated at highway speeds. During both events, the vehicle unexpectedly lost propulsion without warning and without any apparent driver input or mechanical indication beforehand. No warning lights, check-engine lights, reduced-engine-power messages, service transmission messages, or other warning indicators were displayed prior to the failure. The vehicle simply lost power while traveling in traffic. During both occurrences, I was forced to safely maneuver the vehicle to the shoulder of the roadway while rapidly losing speed among surrounding traffic. Once stopped, the vehicle would not resume normal operation until it was restarted. After restarting, the vehicle appeared to operate normally; however, the fact that this condition has now occurred twice raises significant concerns regarding the reliability and safety of the vehicle. Safety Risk This condition presents a significant and immediate safety risk because sudden loss of propulsion during highway operation can leave the driver unable to maintain speed, safely merge, maneuver, or avoid surrounding traffic. The unexpected reduction in speed creates the potential for rear-end collisions, loss of vehicle control, or other traffic accidents, particularly when operating on high-speed roadways. Because the vehicle provided no warning before losing power, there is little opportunity for a driver to take preventive action. Additional Information • Vehicle: 2023 GMC Sierra Denali Ultimate • Engine: 6.2L V8 • VIN: [XXX] • Approximate Mileage: 52,000 miles • Number of Incident INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 55

NHTSA ID

11741004

Incident

May 29, 2026

I was driving down the road at 55 mph on 4/12/2026 and had let off the gas for a 45 mph zone when I experienced a violent downshift of the transmission that squealed the tires momentarily and felt like someone had hit me from behind. It startled me and caused me to lower my speed down to 20 mph. I continued driving to my destination and when I let off of the gas doing 45 mph for a slight curve I had another violent downshift that felt again like someone hit me from behind. I contacted a GMC dealer on 4/13.2026 to see if there was a recall on the transmission that I wasn't seeing online and was told no. I described what I experienced to their service department and was told to flush out the transmission fluid and replace the filter. I did experience another bad downshift at a slower speed (about 25 mph) on 4/13/2026. There wasn't any warnings or lights that came on when these three incidents occurred. When looking online I did see there was a similar recall for 2020-2022 GMC Sierra's where customers were experiencing similar violent transmission downshifts and am wondering if this issue is affecting more than just those three model years.

NHTSA ID

11730979

Incident

Apr 12, 2026

On March 13, 2026 I purchased a 2023 GMC Sierra AT4 Pickup with 3.0 Diesel Engine. While driving on a state highway in a 35 mph zone I started to accelerate as the speed zone changed. The truck suddenly had the rear wheel lock up for a brief time about quarter to half second then the truck proceeded on. This happened as the transmission was downshifting. Then on or about March 24, 2026 I was using the same truck and towing a 4,000 pound enclosed trailer. This trailer was hooked up within all recommended hookup requirements. In a 225 mile trip I experienced the same rear wheel lock up happen 4 random times during the trip. Once this happened at 65 miles and hour had there been snow or ice on the highway the truck may have crashed. This lock up happened while using the truck in tow haul mode. Two times it happened while the truck was being towed with cruise control active and two times it happened while not using cruise control. Truck was brought to Authorized GM Dealer and inspected and truck had no stored codes from transmission related issues. Dealer blamed this for using cruise while towing. I informed dealer this happened while not using cruise as well. Was told to turn off adaptive cruise when towing. I was unable to find anything in the GMC Manual regarding not using cruise while towing. This appears to be an issue with the valve body in the transmission and customer explained this to the dealer but they denied this claim. When these quick moment lockups happen no codes or engine lights show everything on dash appears normal. Customer is bringing truck to another GM Dealer to be tested and examined.

NHTSA ID

11729261

Incident

Mar 24, 2026

Incident Summary: On 2/2/2026, my vehicle was serviced under Safety Recall 25V-274 at an authorized GMC dealership. The service technician performed the mandated diagnostic protocol (including the PicoScope test) and informed me that the engine had "passed" inspection. No internal components were replaced; the remedy was limited to an oil change to a higher-viscosity oil (0W-40) and a new oil filler cap. The Failure: Approximately 48 hours after this "successful" recall remedy, the vehicle suffered a catastrophic engine failure while in operation. The engine failed entirely. The vehicle lost all propulsion while in motion, creating an immediate safety hazard for myself and other motorists. Diagnostic and Risk: The failure has been confirmed by a GMC dealer, who subsequently performed a full engine and radiator replacement. In the 48-hour prior to failure, there were no warning lamps or symptoms; the vehicle had just been cleared by the manufacturer's own diagnostic tools as safe and free of defects. Systemic Concern: This incident demonstrates that the current diagnostic protocol for Recall 25V-274 is insufficient to identify terminal manufacturing defects in the connecting rods and crankshaft of the L87 6.2L V8 engine. The "remedy" of higher-viscosity oil failed to prevent the exact catastrophic loss of propulsion the recall was intended to address. The replaced engine is available for inspection upon request by the NHTSA Office of Defects Investigation.

NHTSA ID

11727522

Incident

Feb 4, 2026

My 2023 GMC Sierra has 60,571 miles for a while now while driving the transmission slips and slams into gears. Recently driving with my kids in the car on highway going 70mph the back brakes locked up multiple times, so scary and dangerous while driving. I now currently have a code P-0747 in the system.

NHTSA ID

11724873

Incident

Mar 8, 2026

While entering the freeway at approximately 45 MPH not towing the rear wheels locked for a second, truck went into the Limp mood, and dash said reduce speed, service transmission. Dealer pulled codes, P0700 and P0747...the order says cause document #6998510."replace spacer plate, check balls and valve." Correction: DTC P0747 set Dealer told me the put the new updated valve in but I don't see that on the repair order? I asked about the GM extended warranty ( I think it's 10 years, 150,000 miles). they said it didn't apply to my vehicle?

NHTSA ID

11723417

Incident

Jan 26, 2026

While traveling on a major Route, the truck just turned off while driving. The truck was stuck in the middle of a two lane major route. Truck would not start or turn on. I was unable to put hazards on or put the truck in neutral. The engine siezed due to the GM recall. After having the engine replaced by a certified GM dealership, a few days later the Throttle body stopped working. Again, keeping me stuck. Certified GM dealership had to replace the throttle body.

NHTSA ID

11721163

Incident

Jan 18, 2026

While driving the vehicle I received dash warnings of temperature rise. Pulled over and saw a large coolant leak coming from right side of engine compartment. Towed to dealership. Dealership informed me that coolant hose coming from heater core was routed by the manufacturer so that it rubbed on the frame. Dealer indicated problem persists on all vehicles and no given, other than replacing the hose and not remedy the problem. New hose will be in contact with frame again, causing inevitable where and breakage. Dealer did not cover under warranty nor did they offer solution for repair other than replacing those hose.

NHTSA ID

11720507

Incident

Feb 22, 2026

The contact owns a 2023 GMC Sierra 1500. The contact stated that while driving in 1st and 2nd gear, the transmission was slipping, causing the vehicle to jerk. There was no warning light illuminated. The vehicle was taken to the dealer, who determined that the valve body needed to be replaced. The vehicle was not repaired. The manufacturer was made aware of the failure and advised the contact to file a complaint with the NHTSA Hotline. The failure mileage was approximately 97,000.

NHTSA ID

11719403

Incident

Feb 1, 2025

Mileage

97,000 mi

The vehicle has experienced repeated incidents of sudden reduced engine power and loss of acceleration while driving. On multiple occasions, while traveling at highway speeds, the vehicle failed to respond normally to throttle input and would not accelerate as commanded and loss of power steering making it difficult to turn the steering wheel and apply brakes. One incident resulted in throwing my truck off the road and luckily we nearly avoided a multi car collision and potential pile with my wife, 8yr old daughter and newborn son in the vehicle at high speeds up to 60/70+ mph but despite avoiding a major life threatening accident to us and other drivers, resulted in striking objects, glass and debris on the side of the road causing damage to my vehicle and then sliding to a complete stop in the ditch off the highway. This creates a hazardous driving situation, particularly when merging into traffic or attempting to maintain speed with surrounding vehicles, increasing the risk of collision. The malfunction appears related to the engine, electrical system, and powertrain. During at least one dealership visit, the reduced power condition was recreated and confirmed by service personnel. However, despite multiple warranty repair attempts, the issue continues to reoccur intermittently. Warning messages have appeared at times, including reduced engine power notifications and check engine indicators, though the condition has also occurred without advance warning. The intermittent nature of the defect makes it unpredictable and unsafe. The vehicle has been out of service for more than 30 cumulative days for warranty-related defect repairs related to this and other electrical issues. Multiple repair attempts have not permanently corrected the condition. The vehicle remains available for inspection upon request. Due to the unpredictable loss of acceleration and prior safety incidents, there are ongoing concerns regarding safe operation of the vehicle.

NHTSA ID

11717754

Incident

Apr 25, 2024

Drastically reduced power on highway resulting in reduced acceleration due to code P0198 engine coolant control valve position sensor. Required me to drive at reduced speed on highway to get to dealer. Safety issue.

NHTSA ID

11717110

Incident

Feb 9, 2026

The contact owns a 2023 GMC Sierra 1500. The contact stated that while driving at an undisclosed speed, the vehicle shuddered while in first gear. The contact stated that the transmission sounded strained and shifted rough before slamming into gear. The vehicle was taken to the dealer; however, no cause for the failure was found. The dealer diagnosed the vehicle and determined that the vehicle was oversteering while turning to the right. The dealer replaced the valve and torque converter. On another occasion, while driving at an undisclosed speed, the vehicle accelerated independently. Most recently, a burned transmission fluid odor was coming from the front of the vehicle and entered the cabin through the A/C vents. There oil stains found on the ground on several occasions. The vehicle was taken back to the dealer and the valve body was replaced, the fluid levels were checked, and the transmission filter was replaced; however, the failure persisted. The contact called the dealer, and the dealer towed the vehicle. The dealer determined that the oil cap was loose. The vehicle remained at the dealer unrepaired. The manufacturer was made aware of the failure, and a case was opened. The failure mileage was 8,496.

NHTSA ID

11715151

Incident

Oct 8, 2025

Mileage

8,496 mi

Vehicle: 2023 GMC [MODEL], Black Widow package, 6.2L L87, 41,078 miles Recall: 25V‑274 / GM [XXX] ; recall remedy performed by Marty’s GMC (Kingston, MA) on 2025 -11-12; oil changed per recall procedure Post‑remedy symptom: intermittent knock starting ~01 - 2025 / about two months after remedy Incident: Jan 23, 2026 — engine seized / loss of propulsion while driving; stranded on highway off‑ramp; vehicle impeding traffic causing dangerous conditions. Codes: OBD scan by passerby indicated camshaft position sensor / correlation error (exact code not captured) Crash/Injuries: none Current status: vehicle at Marty’s GMC since Jan 23; not diagnosed as of Jan 29; GMC case #88159466 Safety concern: sudden loss of motor power in traffic after recall remedy On Friday, Jan 23, 2026, while my daughter was driving, the engine seized / the vehicle lost propulsion and stranded her on a highway off‑ramp. The vehicle was impeding traffic and had to be moved. It restarted briefly and was moved to a safer location but still impeding traffic. A motorist scanned the OBD port and reported a camshaft position sensor / cam-crank correlation error (exact DTC unknown). No crash occurred and no injuries occurred. The vehicle has been at Marty’s GMC since Jan 23, 2026 and as of Jan 29, 2026 it has not yet been diagnosed. I opened a case with GMC Customer Assistance (case #XXX). This is a safety-related loss-of-propulsion event occurring after the recall remedy was completed. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA ID

11714188

Incident

Jan 23, 2026

The contact owns a 2023 GMC Sierra 1500. The contact stated that when the vehicle was started and shifted into drive(D), the accelerator pedal was depressed, and the vehicle responded slowly. While driving at an undisclosed speed, the vehicle decelerated and stopped unintendedly. The "Parking Brake” warning light illuminated. The contact stated that once the vehicle had warmed up, the unintended stopping ceased. The contact stated that the failure was intermittent at first but had become a recurring failure. The vehicle was taken to a local dealer where it was diagnosed and determined that the valve body needed to be replaced; however, the part to complete the repair was on a national back order. The vehicle was not repaired. The manufacturer was informed of the failure. The failure mileage was approximately 60,000.

NHTSA ID

11714126

Incident

Mar 3, 2025

Mileage

60,000 mi

The contact owns a 2023 GMC Sierra 1500. The contact stated that while driving uphill, the vehicle unexpectedly lost motive power. There was no warning light illuminated. The vehicle failed to restart and was towed to the dealer, where it was diagnosed, and determined that the engine block had failed and needed to be replaced. The vehicle was repaired. The contact stated that later, while driving at an undisclosed speed, the vehicle failed to shift into gear properly and jerked abnormally. There was no warning light illuminated. The vehicle was returned to the dealer and was diagnosed with transmission failure, requiring the PCM/TCM to be reprogrammed. The vehicle was repaired. The contact stated that while driving at an undisclosed speed, the check engine warning light illuminated, and the vehicle was taken back to the dealer, where it was diagnosed and determined that the fuel injector and coolant pump had failed and needed to be replaced. The vehicle was not repaired. The manufacturer was made aware of the failure, and a case was opened. The approximate failure mileage was 57,000.

NHTSA ID

11713963

Incident

Jan 28, 2026

Mileage

57,000 mi