2021 Mercedes-Benz C300 Engine Problems
- Complaints
- 8about this part
- Share
- 57%of 14 total for the year
- Median mileage
- 87,039miles
- Trend
- Not enough dataFewer than 15 complaints, too few for a reliable trend.
NHTSA recorded 8 complaints about the engine of the 2021 Mercedes-Benz C300, 57% of the 14 complaints for this model year. Where a mileage was given, the median is 87,039 miles.
Fewer than 15 complaints name this part, so treat the figures as a rough indication only.
Example complaints
Selected from NHTSA records; personal details are removed. They are consumer reports, not findings.
“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. …”
NHTSA complaint #11678865, filed 2025-08“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. …”
NHTSA complaint #11755408, filed 2026-08, 88,000 miles“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. …”
NHTSA complaint #11706514, filed 2025-12, 86,078 miles“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, filed 2024-03“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). …”
NHTSA complaint #11701560, filed 2025-11Related service bulletins
- 11035238Jul 24, 2026Mercedes-Benz AG (“MBAG”), the manufacturer of Mercedes-Benz, has determined that on certain MY 2019-2021 C-Class, G-Class, GLC, GT, S-Class (205, 463, 253, 190 & 222 platforms)…
- 11034064Jun 19, 2026Dear Mercedes-Benz USA Dealers, The part numbers listed in the chart below should no longer be installed, and any existing stock must be returned to your facing PDC. The deadline…
- 11030302Mar 27, 2026Complaint -Check engine light illuminated. -Engine runs rough. -Poor shifting or jerking when accelerating. -Fault codes stored related to mixture formation, injector quantity…
- 11028807Feb 14, 2026Mercedes-Benz AG, the manufacturer of Mercedes-Benz vehicles, has determined that on certain subject vehicles, the engine control unit software does not correspond to current…
- 11028267Feb 2, 2026Complaint -Check engine light illuminated. -Engine runs rough. -Poor shifting or jerking when accelerating. -Fault codes stored related to mixture formation, injector quantity…
- 11028003Jan 23, 2026Dear Mercedes-Benz Owner: In our continuing efforts to ensure the proper performance of Mercedes-Benz products and to enhance the satisfaction of our customers, Mercedes-Benz USA…
- 11027580Jan 10, 2026In our continuing efforts to ensure the proper performance of Mercedes-Benz products and to enhance the satisfaction of our customers, Mercedes-Benz USA, LLC is extending the…
- 11008712Oct 4, 2024Complaint Check engine light on. One of the below fault codes is current in the engine control module (N3/10). P04DB29, P04DB31, P04DB79 Cause Open circuit or high resistance to…
- 11008056Sep 16, 2024Complaint Check engine light on. Fault code P207273 - "Throttle actuator valve is blocked due to ice" stored. Engine may crank and not start. Fault code P210185 may also be…
- 11005314Jul 20, 2024Complaint Yellow Coolant warning comes on in cluster Fault codes below are current or stored in MED41 P0A0500- The actuation of the circulation pump for the low-temperature…
Engine: other model years
| Year | Complaints | Share of year |
|---|---|---|
| 2024 | 2 | 18% |
| 2023 | 2 | 9% |
| 2022 | 2 | 8% |
| 2021 | 8 | 57% |
| 2020 | 8 | 24% |
| 2019 | 17 | 25% |
| 2018 | 34 | 34% |
| 2017 | 77 | 36% |
| 2016 | 94 | 32% |
| 2015 | 127 | 33% |
| 2014 | 2 | 2% |
| 2013 | 8 | 3% |
| 2012 | 5 | 2% |
| 2011 | 10 | 2% |
| 2010 | 13 | 3% |
| 2009 | 16 | 3% |
| 2008 | 31 | 5% |
Other parts of the 2021 Mercedes-Benz C300
3 complaintsAir bags
1 complaintsBack-over prevention (rear camera)
1 complaintsElectrical system
1 complaintsTransmission and drivetrain
1 complaintsVisibility (wipers, defrost, mirrors)
1 complaints
← All problems reported for the 2021 Mercedes-Benz C300
About this data. Data from NHTSA (ODI) complaints, recalls, TSBs and investigations, updated Oct 30, 2026. Complaints are unverified consumer reports and may be duplicated or inaccurate.
To check a specific vehicle for open recalls, use its VIN at nhtsa.gov/recalls. Methodology