2020 Mercedes-Benz GLC 300: sudden loss of power

Filed Oct 26, 2026 · Electrical, Engine · MD

On October 23, 2026, my 2020 Mercedes-Benz GLC 300 unexpectedly lost engine power while I was in traffic, without advance warning. When I attempted to restart it, the engine started, shook, and shut off again. A 12-volt battery warning appeared during the incident. On October 26, a dealership representative told me a software issue caused the shutdown and that a software update was needed. They said the update would be performed at no charge, although I would owe a diagnostic fee. I am concerned that the vehicle could lose power without warning again, especially at highway speeds. I am requesting that the federal safety agency review this incident for a possible safety defect.

Filed Dec 8, 2025 · Engine · CT

The engine in my 2020 Mercedes-Benz GLC 300 suddenly malfunctioned while driving on two separate occasions. The vehicle began shaking violently and lost power without warning. I could not accelerate and had to pull over immediately. I turned the vehicle off and restarted it to regain limited driveability. On the second incident, the power loss was so abrupt that it felt as if I had been rear-ended. I feared the vehicle would stall in traffic and cause a crash. Following these events, the check engine light remains constantly on. The dealer inspected the vehicle and confirmed excessive valve leakage into the exhaust system, requiring a complete cylinder-head replacement. They warned the failure will worsen and could result in sudden power loss again. This defect poses a serious safety risk. If the power loss occurs while merging or at highway speeds, it could easily lead to a rear-end collision. The vehicle has relatively low mileage for such a severe internal engine failure, and I have learned that other owners of this same engine have reported similar issues. Sudden stalling or loss of acceleration places occupants and other drivers in danger. There were no warning messages prior to the failure, and the problem has recurred. The vehicle is available for inspection, and the defect has been confirmed by a Mercedes-Benz service center. This appears to be a mechanical defect in the engine design, potentially involving valve seat failure. An investigation is needed to determine if this issue is widespread and whether a recall or manufacturer action is required to prevent accidents or injuries.

Filed Sep 23, 2025 · Driver assistance · CA · crash · 3 injuries

On August 15, 2025, I was driving my Mercedes-Benz GLC 300 4MATIC on the freeway under normal conditions. Without any warning lights, error messages, or prior signs of mechanical issues, the vehicle suddenly and completely lost power. The accelerator pedal became unresponsive and felt locked, and the vehicle came to an abrupt stop in the middle of an active freeway, in the second lane from the left. I had no ability to control or prevent the stoppage. This unexpected power loss directly led to a rear-end collision. The vehicle behind me sustained severe front-end damage, including airbag deployment. My passenger and I were in shock and suffered whiplash and physical injuries, with pain and bruising following the impact. I suspect the most likely causes may be an Electronic Throttle Control failure or a false activation of an Active Safety System. I opened a case with MBUSA (Case #16298894) immediately after the incident, but I have not received any updates on the investigation. This was a dangerous and life-threatening failure, and I am deeply concerned that it could occur again to other drivers if not addressed.

Filed Aug 6, 2025 · Engine · MS

With approximately 57,500 miles, the car began idling roughly, misfiring and losing power. The dealership has diagnosed it with a cracked cylinder head which will require a replacement at a cost of $9,765.00. The dealership indicated this is a common issue with the M264 engine (rear wheel driver) in the GLC300 and the M260 engine (the front wheel drive version) has already had a service extension for 15 years/180,000 miles. This type of failure should not occur at this mileage or even significantly more.

Filed Apr 28, 2025 · Engine · MS

Some M264 Engines are predisposition to premature cylinder head failure, this issue can cause significant misfire issues. It also leads to a costly repair. We experienced issues with a P219D code , we had the coils and plugs replaced on a 2020 GLC 300 with 38.5 k miles. We assumed that this issues with a misfire and check engine light were corrected. My wife was turning onto [XXX] in Pascagoula MS last week, the car misfired and stalled with cars and semi trucks rapidly approaching, several cars had to slam on breaks and this issues almost caused a significant wreck. She had to pull over to gain her composure, the car would not over above 2k RPMs. I showed up and was able to to restart the car , I immediately drove it back to the repair shop. The shop bore scoped the #2 cylinder, the valve seating is significantly damaged, thus causing a significant loss of engine power / misfire in cylinder 2. I reached out to Mercedes Benz USA and was advised to take the GLC300 to the dealer that sold us the car. At present the is being evaluated by the MB dealer. MB USA is well aware of issues regarding cylinder head failure. There is actually a low mileage GLC 300 at MB of Mobile with the same problem as our MB. They have sent out service bulletins to every MB Dealership in the US regarding this issue. Likewise they have extended the warranty on several MB models that share the same engine that are mounted for front wheel drive cars, M260 engine. The M264 is an identical engine that is mounted for rear wheel dive vehicles. It is beyond obvious that a significant loss of engine power poses a threat to the driver/occupants and other vehicles/occupants on the road. MB USA is well aware of this issue with their engines. Not only do they have a service bulletin regarding this matter , they have repair protocols which include a cylinder head replacement. This is a consumer and safety issue that needs to be corrected on applicable GLC 300 models. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMAT