What 23 owners told NHTSA about the 2024 Mercedes-benz GLC Coupe

While driving my 2024 Mercedes-Benz GLC 300 on California highways, the vehicle has repeatedly experienced sudden uncontrolled deceleration, unexpected transmission downshifts into 2nd gear, severe transmission jerking, and complete loss of accelerator response. The first major incident occurred on March 7, 2025, while traveling on Interstate 5 at approximately 70 mph. The transmission suddenly jolted and downshifted directly into 2nd gear. The vehicle immediately lost power and slowed to approximately 20 mph without warning. I exited the highway and restarted the vehicle before it temporarily resumed normal operation. A second major incident occurred on May 7, 2026, while driving on Interstate 5 near Flag City, California at approximately 65 mph. The vehicle suddenly decelerated uncontrollably to approximately 20 mph. The transmission again shifted directly into 2nd gear, and the accelerator pedal became completely unresponsive. I was forced to make an emergency stop on the shoulder of the freeway with hazard lights activated due to the risk of being rear-ended by high-speed traffic and trucks. A third incident occurred on May 13, 2026, while accelerating onto Highway 99 in Modesto, California. During a shift from 4th to 5th gear, the transmission jerked violently and the vehicle suddenly lost power while merging into highway traffic. The vehicle has been taken to Mercedes-Benz of Stockton multiple times for diagnosis and repair attempts. The dealership has performed software updates and extensive testing, and dealership personnel have personally verified the transmission defect during road testing. Mercedes-Benz engineering has also become involved in the diagnosis process. However, the defect remains unresolved. This defect creates a serious highway safety hazard due to sudden loss of propulsion, uncontrolled deceleration, and loss of accelerator response while driving at freeway speeds.

NHTSA ODI 11740380

The vehicle has an ongoing transmission downshifting malfunction. The powertrain unexpectedly downshifts while driving, causing sudden changes in speed and unstable vehicle behavior. The issue can be inspected at any time, as the defect occurs intermittently and has not been repaired. This malfunction puts my safety and the safety of others at risk because the vehicle can slow down abruptly or shift aggressively without any input from the driver. This can create dangerous situations in traffic, especially at highway speeds or during acceleration. The problem has been reproduced and observed multiple times by the Mercedes-Benz dealership. I have taken the vehicle to the service center repeatedly for this same issue. Most recently, the vehicle remained at the service center for 10 consecutive days, but the defect was not resolved. The vehicle has been inspected by Mercedes-Benz technicians on several occasions. Despite multiple repair attempts, the issue continues to occur. There were no warning lamps or dashboard messages prior to the malfunction. The issue first appeared months ago and has persisted despite repeated service visits and repair attempts.

NHTSA ODI 11700853

•Incident Details: •Both sudden shutdown incidents •“12V Battery” warning (first incident) •“Stop - Switch Off Vehicle” warning (second incident) •That it happened with children in the car on a tollway Safety Concerns: •Loss of power steering/braking •Risk of collision •Repeated failures on a 1-year-old vehicle

NHTSA ODI 11677934

I am writing to report a critical safety issue with my 2024 Mercedes-Benz GLC300, VIN: [XXX] , which I purchased on [XXX], from Mercedes-Benz of Walnut Creek, CA, with 9,500 miles. On [XXX], while driving on [XXX], the vehicle suddenly lost power, the transmission downshifted to 2nd gear, and the accelerator became unresponsive. I was forced to drive at 20 mph for 20 minutes on a busy freeway, posing a severe risk of a rear-end collision. I managed to exit the freeway, but this incident could have resulted in a serious accident. This failure may be related to prior recalls of the 2024 GLC300, including issues with a defective 80-amp fuse (February 2024) and a loose 48-volt battery ground connection (March 2024), both of which can cause power loss. I urge the NHTSA to investigate this incident to determine if it warrants an expanded recall or further action to protect other drivers. I have notified Mercedes-Benz of Walnut Creek CA and Mercedes-Benz USA, demanding an investigation and a refund under the California Lemon Law. Please confirm receipt of this complaint and provide an update on any investigation. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA ODI 11647082

When stopped at a light or stop sign, Vehicle will Jerk forward as If hit from behind. Very surprising and dangerous. Very intermittent. The has happened many times. Vehicle will at times have rough downshifts. Ie. overdrive (9th) to (8th) gear. also intermittent. This has happened multiple times. Vehicle was taken to the dealer twice for a total of 50 hours in the shop. The first service time no problem was found, diagnostics did not show problem. Aug 22 to Aug 30, 2024. The second service time Oct 3 to Nov 14, 2024. Problem was duplicated by the technician. Vehicle diagnostics still did not show a problem. Technician replaced the transmission valve body, did various software checks at the request of the factory. The engine control unit was then changed based on data supplied to the factory. At this point technician checked the car and dealers believes car is fixed. Vehicle has been returned to us on Nov 14 2024. We have requested the vehicle be bought back or replaced.

NHTSA ODI 11625278

There wasn't a field for my exact issue but my exact issue along with many others is the lack of power when accelerating in first gear. The car has an extremely numb feeling when starting out in first gear and does not takeoff like it should. There have been many Times where I accelerate and the car hesitates then I get a transmission jolt Or the car just does not accelerate immediately when I push on the gas from a stop. This is causing me to not pull out in front of cars in fear the car will hesitate which is a safety issue. this has been going on ever since we got the car a few months ago. The dealership says the vehicle is "operating as designed however this is a poor excuse" i've had owned dozens of vehicles in the past 28 years and not one of them has had poor acceleration like this. I've owned cars with a quarter of the horsepower of this vehicle that accelerate better from first gear.

NHTSA ODI 11617155

Brand new '24 GLC300 4MATIC. Engine light came on with no error message. Brought it in for service. Miscellaneous engine repair states: "Found current code POA7F00 in drivetrain control unit. Followed LI54.10-P-077250. Cleared codes. Drained 48V battery to below 25% SOC. Charged vehicle to 70% SOC. Job complete." Service foreman mentioned that the service performed may not resolve issue. He contacted Mercedes-Benz Engineering and said no fix at this time and no ETA. Left service with no more engine light on. However, it didn't take long, and the engine light came on again. I called service again, and I was asked to take the car back in to be sure it is not anything else. Took my vehicle back, and service foreman diagnosed the issue. Code is the same as before with issues on the 48V battery. Service foreman is unsure of the exact issue. Mercedes-Benz Engineering did not provide details of the problem. I believe this issue poses a safety risk without knowing for sure what is the real cause and what might be the effects on the vehicle. This GLC is my family daily use, and it has become a big safety concern on the road. Service was very helpful and accommodating with my vehicle's issues. Unfortunately, fix is unknown from Mercedes-Benz to be able to resolve. I have also called the Mercedes-Benz Customer Care, 800-367-6372. Unfortunately, there is nothing they can do. I've asked to open a case. Case # [XXX] INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA ODI 11566165