2020 Mercedes-Benz GLC 300: misfire or rough idle

Filed Dec 3, 2025 · Engine · GA

My 2020 Mercedes-Benz GLC 300 experienced a complete engine failure at ~51,000 miles, shortly after a major repair for a known defect. Initially, the vehicle showed a misfire on cylinder #3, which was diagnosed at RBM of Alpharetta as low compression due to valve seat damage, matching MB TSB LI01.30-P-072328. The cylinder head was replaced in Aug 2025. About two months later, while driving under normal conditions, the vehicle made a loud cranking/knocking noise and completely stalled in traffic without any check engine light or warning. This sudden stall posed a serious safety risk. The vehicle was towed to the same dealer, who has now diagnosed the engine as fully seized and recommended a complete engine replacement. I had also completed the 50,000-mile scheduled service at the same dealer shortly before this failure. Despite this being clearly linked to a known design defect, Mercedes-Benz USA has declined to provide further assistance or goodwill coverage. I am reporting this to highlight both the mechanical failure and the safety risk—this engine seizure occurred without any prior warning lights and could have resulted in a crash. I believe this reflects a systemic failure with the M264 engine in GLC 300s, affecting vehicle reliability and road safety. MBUSA has not provided a written explanation for their denial. I am concerned this issue may affect other GLC 300 owners and deserves investigation or recall consideration.

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

Filed Jan 13, 2025 · Engine · TX

Car was running rough so I took it to the mercedes benz dealer they diagnosed the problem as cylinder 1 misfire and and cylinder head needed to to be replaced which I did $5500 dollars later this is a common problem and Mercedex Benz needs to recall the engine and reimburse me

Filed Aug 9, 2024 · Engine · AL

Engine began unpredictably running rough. Would lose ability to accelerate, in traffic. Engine light came on. Originally took to dealership, computer indicated a “misfire cylinder 2” was told by mechanic at dealership it was possibly “bad gas” and they cleared all codes. Continued to get worse. Took vehicle to a licensed “Mercedes Doctor” mechanic who had to replace cylinder head to correct. Vehicle is now running better than new!

Filed May 16, 2024 · Engine · 25,000 miles · CA

The contact owns a 2020 Mercedes-Benz GLC300. The contact stated that while driving at an undisclosed speed, the engine misfired. In addition, the check engine warning light was illuminated. The contact was turned off and restarted the vehicle. The contact stated that the vehicle drove as needed. The contact stated that the vehicle was taken to an independent mechanic however, the failure was unable to be duplicated. The vehicle was not repaired. The contact stated that the failure occurred intermittently for several months. The vehicle was taken back to the independent mechanic where it was diagnosed with a failed engine vent seat and the engine vent seat needed to be replaced. The vehicle was not repaired. The contact was advised to take the vehicle to the dealer. The vehicle was taken to the dealer where it was diagnosed with a failed engine vent seat and the engine vent seat needed to be replaced. The vehicle was not repaired. The manufacturer was made aware of the failure and a case was filed. The failure mileage was approximately 25,000.