2021 Mercedes Benz C 300 problems

ENGINE

The contact owns a 2021 Mercedes-Benz C 300. The contact stated that while depressing the accelerator pedal, there was a loud knocking sound coming from the engine compartment while accelerating. There were no warning lights illuminated. The vehicle was taken to the dealer to be diagnosed, and it was determined that the spawn rod was fractured, causing engine failure. The contact was informed that the engine needed to be replaced. The vehicle was not repaired. The contact stated that the engine was previously repaired because of the head gasket failure in 2024. The manufacturer was informed of the issue, and a case was opened. The failure mileage was approximately 88,000.

NHTSA complaint #11755408 — an unverified report by a vehicle owner.

FUEL SYSTEM, GASOLINE

The contact owns a 2021 Mercedes Benz C. The contact stated that while driving on the highway, the vehicle began to lose power, riding rough. The check engine light illuminated. The vehicle was towed to the dealer where it was diagnosed with a fuel injection failure. The vehicle read diagnostic code P1CEF85. The manufacturer was made aware of the issue. The approximate failure mileage was 60,000.

NHTSA complaint #11738727 — an unverified report by a vehicle owner.

VISIBILITY:SUN/MOON ROOF ASSEMBLY

I am reporting a safety defect involving the panoramic sunroof on my 2021Mercedes-Benz Coop vehicle. The panoramic sunroof has malfunctioned due to an apparent design or manufacturing defect. The sunroof fails to open / close and makes grinding or popping noises which malfunctioned unexpectedly. This issue occurred without misuse and during normal operation of the vehicle. The defect creates a safety concern because it can distract the driver, allow water intrusion that may affect electrical components, and/or cause sudden glass or mechanical failure while driving. The vehicle has been taken to a Mercedes-Benz dealership for diagnosis and the issue was not resolved due to denied coverage. I was informed that the repair would be costly despite the issue appearing to be a known defect in Mercedes-Benz panoramic sunroof systems. I believe this defect may affect other Mercedes-Benz vehicles with panoramic sunroofs and should be investigated for a potential safety defect or recall.

NHTSA complaint #11712287 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11706514 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11701560 — an unverified report by a vehicle owner.

FUEL/PROPULSION SYSTEM

My car had a coolant leak last year a hose broke and I have a 2021. My son’s mercedes sis the same thing on 11/23/2025. I have researched ma y others with this same issue. There should be a recall on that hose or whatever the problem Is.

NHTSA complaint #11701496 — an unverified report by a vehicle owner.

FUEL/PROPULSION SYSTEM

While driving car on Sunday 10/5, it suddenly failed to respond to gas pedal pressure. The car stopped accelerating and rather slowed to 15 MPH, almost causing a car from behind to hit me in the rear side.

NHTSA complaint #11691568 — an unverified report by a vehicle owner.

POWER TRAIN

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.

NHTSA complaint #11678865 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11678865 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11643229 — an unverified report by a vehicle owner.

BACK OVER PREVENTION: SENSING SYSTEM: CAMERA

Rearview camera not displaying any image when transmission is put in reverse.

NHTSA complaint #11623522 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11579561 — an unverified report by a vehicle owner.

ELECTRICAL SYSTEM

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. Took in for inspection, gave no reasoning from original dealer service dept, other then a top off done. Vehicle drives rough. While driving 70mph, a vehicle behind was approaching quick when I went to excel to merge vehicle seemed to be slipping in gear/slow down. No warning lamps on, Quickly decided/managed to merged to next lane so vehicle behind didn’t hit us as we were slowing down With 2 children in the back seat. decided to exit to nearest exit to pull off as it felt unsafe to drive, as exiting and slowing down vehicle began to shake, knock, and make loud bangs. Managed to pull over, and check dash for messages for any type of warnings. No warning lamps, but many symptoms of a faulty unsafe vehicle. Had vehicle towed to original dealer service for diagnosis and report the unsafety incident that occurred with absolutely no warning lamps. Inspection lead to repair of engine but nothing done about no warning lamps/electrical system

NHTSA complaint #11568290 — an unverified report by a vehicle owner.

ENGINE

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. Took in for inspection, gave no reasoning from original dealer service dept, other then a top off done. Vehicle drives rough. While driving 70mph, a vehicle behind was approaching quick when I went to excel to merge vehicle seemed to be slipping in gear/slow down. No warning lamps on, Quickly decided/managed to merged to next lane so vehicle behind didn’t hit us as we were slowing down With 2 children in the back seat. decided to exit to nearest exit to pull off as it felt unsafe to drive, as exiting and slowing down vehicle began to shake, knock, and make loud bangs. Managed to pull over, and check dash for messages for any type of warnings. No warning lamps, but many symptoms of a faulty unsafe vehicle. Had vehicle towed to original dealer service for diagnosis and report the unsafety incident that occurred with absolutely no warning lamps. Inspection lead to repair of engine but nothing done about no warning lamps/electrical system

NHTSA complaint #11568290 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11525102 — an unverified report by a vehicle owner.

AIR BAGS

The contact owns a 2021 Mercedes-Benz C300. The contact stated while driving at an unknown speed, there was a burning odor inside the vehicle. The contact stated the passenger side air bags was enabled warning light was illuminated. The contact also stated the vehicle made an abnormal noise. The contact took the vehicle to the local dealer but was unable to duplicate the failure. The manufacturer had not been informed of the failure. The failure mileage was unknown.

NHTSA complaint #11453645 — an unverified report by a vehicle owner.