2021 MERCEDES-BENZ C 300 Engine Problems

The contact owns a 2021 Mercedes-Benz C300. The contact stated that while driving at an undisclosed speed, the vehicle stalled and failed to exceed 30 MPH, with the check engine warning light illuminated. The vehicle did not require a restart. The contact also stated that while stopped at a traffic light, the vehicle was shaking abnormally. The vehicle was taken to an independent mechanic, where it was diagnosed and determined that there was a misfire in cylinder #2. The contact was informed that the cylinder head needed to be replaced. The vehicle was not repaired. The vehicle was then taken to the dealer, where the same diagnostic information was provided, and the contact was informed that the cylinder head needed to be replaced. The vehicle was not repaired. The manufacturer was made aware of the failure. The approximate failure mileage was 86,078.

2021 Mercedes-Benz C300 with M254 2.0L turbo engine experienced sudden cylinder head failure at 44,000 miles due to manufacturing porosity in the cylinder head and camshaft bore scoring. Dealer confirmed defect. This is a known, recurring issue on 2021–2023 M254 engines with multiple documented failures under 50k miles. Sudden loss of compression and misfires create a safety risk of engine failure or fire while driving. TSB NUMBER LI07.16-P-074000 (February 2023, updated multiple times). This is a known production/early break-in issue with the M254 engine, not the result of owner misuse or delayed maintenance.

My C300 only had about 42,000 miles and was less than 5 years old. Just after the factory warranty expired, the engine was running rough and hot, and "check engine" light illuminated. My local garage quickly diagnosed the problem as a failed cylinder head, stated that it is common with Mercedes 4-cylinder engines from about 2017, and said Mercedes may cover it since it is a "known problem" and shouldn't happen with that mileage. I was charged $7,860 by my local Mercedes dealer, and despite multiple contacts with MercedezUSA, they refuse to acknowledge this is a problem or cover the cost, although in on-line the forums some people were arbitrarily reimbursed. There should be a recall to check for this obvious defect and should be covered. This defect can cause sudden engine failure and is a significant hazard to the driving public.

Cylinder head needed to be replaced on the M264 engine at 35,000 miles. The replacement part is also known to be defective for the same reasons. This is a common defect known to the manufacturer and they have not issued a recall. My concern is that of a roadside breakdown that would endanger my wife and myself. Thank you for your consideration.

the check Engine light fault code P012D12 The pressure sensor upstream of the turbocharger had a short circuit to positive. Found Kink wire on upstream pressure sensor. A short circuit to positive. Electrical Wire replaced.

First day leasing the vehicle within 6 hours lights malfunction and malfunction warning on dash to seek workshop, vehicle was taken for inspection to original dealer (Mercedes Benz of Bakersfield). During inspection I added additional concerning complaints about passenger door not closing correctly/wind noise seeping through when closed, and hood not closing promptly. One month into leasing vehicle passenger window malfunction, took for inspection and repair to original dealer (MBofBakersfield). Concerned with caution for me, my family, and friends when in that vehicle for giving faulty signs so early. One year into leasing vehicle check coolant warning on dash, took for inspection to original dealer. I am now more concerned as it went form electrical to coolant components losing coolant with no reasoning from original dealer service other then a top off. Vehicle drive is rough. 1 year and 6 months into leasing vehicle, again check coolant warning on dash....

Piston Connecting Rod broke and left the engine making holes in both sides of the block; Mercedes Benz rejected any responsibility because the car has a branded title. Currently a new engine (brand new) is being installed, my concern is that what will happen if the new engine has the same defective part and blew up again.