2020 Mercedes-Benz C-Class Powertrain & Transmission Problems

I purchased this 2020 Mercedes-Benz C300 only two months ago and have driven it less than 3,000 miles. The Carfax report shows consistent maintenance and regular service history by prior owners. While driving, the check engine light came on and the vehicle began shaking and running roughly. Diagnostics by Peachtree Imports (10/03/2025) and later by Mercedes-Benz of Atlanta South confirmed Cylinder #2 failure on the M264 2.0L engine at only 26,589 miles. The dealer’s report states: “Cylinder #2 mixture formation out of spec. Fault occurred due to worn exhaust valve seat. Cylinder head replacement required.” Estimated repair cost: $10,470.66. This causes misfire, loss of power, and unsafe drivability. The failure matches Mercedes-Benz Technical Service Bulletin LI01.30-P-072328 (2021), which documents valve-seat leakage in M264 engines requiring head replacement. The vehicle is outside warranty but has extremely low mileage, and MBUSA Case #18392667 remains unresolved. It is also important to note that the M260 engine, which is mechanically identical to the M264 but mounted transversely, has already received a warranty extension from Mercedes-Benz for the same cylinder-head and valve-seat defect. This indicates a systemic issue across both engine families, presenting a safety risk of sudden power loss or engine stall during operation.

My wife was driving our 2020 Mercedes Benz C300 coupe near our house and the engine light came on. Then the car could not be driven over the speed of 30 miles per hour. Then it stopped and had to be towed. Fortunately, she was able to avoid being hit by other vehicles.The car only has 25219 miles. It was towed to a mechanic who performed a diagnostic test which provided a series of codes regarding the malfunction. Three codes were related to the CAMTRONIC camshaft system and its Solenoid ( Codes: P003C-53; P34AE-00; P34AD-09). Camshaft position actuators Failure codes: P34AD; P34AE. The way it happened could have resulted in damage, serious injury or death since the car suddenly stopped. The car is well maintained. We believe that there is a manufacturer's defect since this is a garaged vehicle that is well maintained and has low mileage.

The car will randomly go into a neutral condition while driving the car. This occurs about once per month, sometimes more often. I will come to a stop for a light or stop sign, upon green light I release the brakes and then gas only to find the engine free revving and the car will not move. I must place the car in Park and then Drive again in order for it to move forward. I have brought this up with Mercedes multiple times and eventually had the transmission replaced. 2 days later, the same thing happened. They do not have a repair available and are dragging their feet to fix. There is a systemic defect in the 9G tiptronic transmission. There are other reports of this transmission going into a "neutral" condition. With the C43 being a relatively lower production class in the C class lineup, I suspect the issue has not made the attention that a higher production vehicle would. I have video with the car 'in gear' and not able to move. And video evidence of the of the transmission glitch.

This has happened a couple of times to me so far. I have been driving down the road (today it was the highway) and my car fell out of gear into neutral and would not go back into gear unless I restarted the car. Every time it has happened, I have had to coast it to a safe spot to restart the car to get it back into gear. Not having power and needing to coast it to safety is a risk to others because I have no control to get myself to safety in some situations. No dealer has been able to reproduce it because of how infrequently it happens. It has happened 3 or 4 times in the last 15k miles. There were no warning messages or indications that it happened or was going to happen and no parts have been inspected. It is really scary when it happens and I hope it dosen't happen to anyone else.

Car randomly goes into neutral despite being in D drive mode. Often at stop light, after the light turns green, the car revs up but is not in gear despite in 'D' drive. I have to shift to park or turn car off then on to get it to go again. This has happens multiple times since new. This is very random and distressing when it happens. Car has been evaluated multiple times at the dealership. There are no trouble codes thrown. The car otherwise works and has no other problem. The technician (off the record) told me there is a known issue when he contacted Germany. Official response to me is that it is perfectly fine.

CEL with multiple cylinder misfires. Oil leak on top side of engine bank 2 in valley of injectors. Multiple codes for turbo charger faults and also clogged catalytic converters. Dealer confirmed and manufacturer denied federal emissions warranty on vehicle. Due to a modification that plays no role in the power train.