151 of the
669 complaints filed about the Mercedes Benz C 300
are about the engine —
23% of everything owners reported.
The worst model year for it is 2017.
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.
2017 Mercedes c300 the switchover valve in the diagnostic module of the evaporative emission control system is jammed open. This issue was called for recall for models 2018 or later, but 2017 was not part of it.
NHTSA complaint #11753176 — an unverified report by a vehicle owner.
DRIVING A 2024 MERCEDES C300 ON THE FLORIDA TURNPIKE IN THE LEFT LANE AT 70 MPH THE ENGINE SUDDENLY SLOWED DOWN. WHILE THE VEHICLE SLOWED IN HEAVY TRAFFIC I WAS ABLE TO MERGE TO THE OUTSIDE LANE WHERE IT STOPPED. I CALLED MERCEDES EMERGENCY WHO SUGGESTED WAITING A WHILE AND TRY STARTING THE VEHICLE . AFTER A FEW MINUTES I WAS ABLE TO START THE VEHICLE AND DRIVE IT TO THE DEALER. THE DEALERS COMPUTER ACKNOWLEDGED THE STOPPAGE AND AFTER THREE WEEKS AND 500 MILES DRIVEN BY THE DEALER WAS NOT ABLE TO DETERMINE THE CAUSE AND PLANS TO REPLACE THE ENGINE COMPUTER. I AM [XXX] OLD AND AFRAID TO DRIVE THIS CAR AND WANT TO END THE LEASE. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)
NHTSA complaint #11751377 — an unverified report by a vehicle owner.
Throttle body and accelerator pedal position sensors failed. Component is available for inspection upon request. Independent service center confirmed failure on 1/3/2026 with 6 stored fault codes: P2101, P0122, P0222, P0123, P0223, P2135. Vehicle shuts off while driving without warning at various speeds. Loss of power steering and power brakes occurs when engine stalls, creating immediate risk of crash, injury or death to occupants and other drivers. Manufacturer customer service confirmed in writing 4 times that engine shutting off while driving is a safety issue and that these exact codes match Service Campaign 2022090005. On 1/7/2026, manufacturer denied campaign applies to this vehicle and refused no-charge dealer inspection, demanding customer pay diagnostic fees to confirm defect they already documented. Vehicle has not been inspected by manufacturer or dealer because manufacturer refuses free inspection. Check engine light illuminated prior to stall events. Manufacturer has actual knowledge of safety defect under 49 U.S.C. 30118 and is creating financial barrier to repair of defect covered by their own service campaign. Request NHTSA investigation and order manufacturer to repair under Service Campaign 2022090005 at no charge.
NHTSA complaint #11747712 — an unverified report by a vehicle owner.
Car fails to accelerate past 25 mph when entering roadway. Roadway area is 45mph and vehicle would not accelerate to reach safe levels. This out myself and occupants of my vehicle in danger as traffic is already at the 45+ mph limit. Vehicle has 30,000 miles. Engine light came on after incident.
NHTSA complaint #11745068 — an unverified report by a vehicle owner.
Upon starting engine while parked the engine vibrated roughly then stopped. Engine light and coolant light illuminated but shut off. Vehicle proceeded as normal, however, as I proceeded for the highway about 1 - 1/2 blocks and approximately 1,200 feet before approaching highway the vehicle 1200 abruptly lost acceleration; engine light and coolant light illuminated again, then engine abruptly shut down in the middle of the road causing a severe safety hazard. Putting myself and others at risk. There were no symptoms of the problems prior to the failure. Coolant leakage; sluggish engine/acceleration; jerking acceleration; coolant light illumination steady.
NHTSA complaint #11738906 — an unverified report by a vehicle owner.
The contact owns a 2017 Mercedes-Benz C300. While driving at approximately 15 mph, the contact observed smoke emanating from under the hood. The vehicle was driven to her work location and parked. Upon exiting the vehicle and opening the hood, she observed orange flames coming from the engine compartment. A parking attendant extinguished the fire, and a police and/or fire report was filed. The vehicle was towed to a dealer and diagnosed with a fuel line leak that caused the engine harness to come apart. The leaking fuel hose from the high-pressure fuel pump caused damage to the high-pressure pump, engine harness, vacuum transducer, and coolant feed line from the thermostat to the firewall. The following components needed replacement: high-pressure fuel pump, rubber fuel hose, engine harness, pressure transducer, and intake manifold. The vehicle was repaired. Five months later, the contact experienced another failure she believes was associated with the engine fire. While parked and attempting to start the vehicle, it did not start. The vehicle was towed to a dealer and diagnosed with a faulty starter that needed replacement. The vehicle was not repaired. The manufacturer was notified of the failure. The failure mileage was 65,422.
NHTSA complaint #11738037 — an unverified report by a vehicle owner.
Vehicle has ongoing and recurring electrical and engine-related defects that affect safe operation. The primary systems involved are the electrical system, engine ignition system, and powertrain. The vehicle is available for inspection upon request. Prior service records show issues beginning in 2020 involving repeated electronic system failures requiring multiple repairs and component replacements. Since purchasing the vehicle in April 2023, the vehicle has developed more serious failures, including: – September 2024: Check engine light with loss of power and inability to exceed safe driving speeds – October 2024: Engine misfiring due to ignition coil failure requiring replacement of ignition components – September 2025: Additional ignition coil electrical fault (code P0353) The problem has been reproduced and confirmed through dealership service inspections and diagnostic reports. Warning indicators, including the check engine light, appeared prior to failure events. These defects create a safety risk due to potential loss of power, engine failure, and unreliable vehicle operation while driving, which could increase the risk of an accident. The issues have required multiple repairs without permanent resolution and appear to be ongoing and worsening over time.
NHTSA complaint #11733212 — an unverified report by a vehicle owner.
The contact owns a 2020 Mercedes-Benz C300. The contact stated that while at a stop, the vehicle failed to accelerate as intended. There was no warning light illuminated. The dealer was not contacted. The vehicle was not diagnosed or repaired. The manufacturer was made aware of the failure and referred the contact to the NHTSA Hotline to report the failure. The failure mileage was approximately 100,000.
NHTSA complaint #11731613 — an unverified report by a vehicle owner.
Check engine light for P052E which has been coming and going off for years now. Now the check engine light is there permanently. I spoke to Mercedes Benz customer service and requested for them to fix the problem now that the light is on permanently but they refuse to fix it because the car has 222,000 miles on it. This should be a recall from the manufacturer not an extended warranty coverage. The Mercedes dealer in Valencia California told me they now only do a software update and put a plug cap on the sensor and want to charge me $850 even though this should be a recall
NHTSA complaint #11725960 — an unverified report by a vehicle owner.
I am reporting a catastrophic repeat engine failure on my 2020 Mercedes-Benz C300. On October 9, 2025, with 26,589 miles, the vehicle suffered a Cylinder 2 failure (exhaust valves), causing a dangerous loss of power in traffic. I paid $4,100.43 for a $10,000 plus cylinder head replacement at an authorized dealer (Mercedes-Benz of Atlanta South) on November 13, 2025. Following the repair, the vehicle continued to exhibit multiple 'Check Engine Oil Level' warnings. On February 4, 2026—less than 90 days after the major repair—the engine suffered a total catastrophic failure. The dealer now states the entire engine requires replacement. This repeat failure of a critical engine component at low mileage poses an unreasonable risk of stalling or sudden loss of propulsion on high-speed roads. I am aware of the January 2026 Mercedes-Benz warranty extension (NCU 30-P-072328) for this specific M264 engine defect, which confirms a known manufacturing flaw that the current dealership repair process failed to remediate, leaving me in an unsafe vehicle.
NHTSA complaint #11718583 — an unverified report by a vehicle owner.
While driving on highway, the engine light came on, a diagnostic test was performed by dealer, oil control valve defected) This could cause engine to lock up while driving, a serious safety concern. I contacted Mercedes Benz corporate office seeking help, because of factory defect. They're not assisting me with this extreme safety matter!!
NHTSA complaint #11712677 — an unverified report by a vehicle owner.
Check engine light comes on, Error Code P052E, after a lot of research, this is a known defective part by Benz. Huge safety issue not addressed by them. Very costly to fix for a customer. There is a new and improved replacement part from Benz indicating they are aware of the faulty old parts that are currently in those cars but yet they have failed to do a recall.
NHTSA complaint #11709871 — an unverified report by a vehicle owner.
While driving at approximately 65 mph on the I-405 freeway in Irvine, CA during rainy conditions, my 2019 Mercedes-Benz C300 suddenly and completely lost acceleration without warning. At the same moment, a Check Engine Light illuminated on the dash. I was forced to coast across all lanes and stop in the emergency shoulder in a very unsafe area with high-speed traffic passing close by in low visibility rainy conditions. Multiple vehicles nearly struck us, including one that had to emergency brake directly behind my car in the shoulder. I contacted AAA and the vehicle had to be towed because it was not safe or driveable. My girlfriend was also in the car and both of us experienced significant fear and distress during and after the incident. My mechanic retrieved fault code P019185 and stated this is a known software problem with the engine control unit that requires a Mercedes software update and reset of mixture adaptations per a manufacturer LI/service document. This means the manufacturer appears aware of the defect and the required software fix, yet I received no recall notice or safety warning. A sudden total loss of engine power at highway speeds creates an extreme crash risk and life-threatening danger to the driver, passengers, and surrounding traffic. There have been other serious drivability issues with this vehicle in the past (misfires, coolant pipe failure, etc.), but this incident was the most dangerous. I am reporting this because this defect appears safety-related and could easily cause a fatality if it happens to someone else at freeway speeds. Diagnostic Note from official Mercedes-Benz Fletcher Jones of Newport Beach Mechanic: “FAULT CODE P019185, WILL START WITH PERFORMING THE SOFTWARE UPDATE OF ME CONTROL UNIT, RESET THE MIXTURE ADAPTIONS PER LI DOCUMENT AND RECHECK.” Tow Provider: AAA — tow confirmation available if needed.
NHTSA complaint #11708992 — an unverified report by a vehicle owner.
This vehicle was brought to an authorized Mercedes-Benz dealership for regularly scheduled maintenance. Shortly after this service, the vehicle began experiencing significant issues including difficulty accelerating, engine hesitation while driving, and noticeable shaking at idle. This car has never overheated. The vehicle was returned to the dealership for inspection. The dealership diagnosed a cracked cylinder head and advised that the repair requires replacement of the cylinder head at an estimated cost of approximately $11,000. The failed component is available for inspection and the vehicle is currently at the dealership. The vehicle has approximately 46,000 miles, has been regularly maintained, garaged, and driven under normal conditions. These symptoms created engine performance issues that could result in loss of power or inability to accelerate while driving, creating a potential safety risk, especially in traffic or at highway speeds. I regularly transport my young grandchild in this vehicle. The possibility of sudden engine failure, loss of power, or breakdown while driving raises significant safety concerns for myself and any passengers, particularly a young child. The failure has been confirmed by an authorized Mercedes-Benz service center. During my own research, I discovered there have been recalls involving similar engines for the same model year, as well as multiple owner complaints reporting similar engine or cylinder head failures on this vehicle. I contacted Mercedes-Benz customer care on December 17, 2025, after receiving the dealership diagnosis, and was advised that I would receive a response within 72 hours. As of today, I have not received any response. I attempted to call customer care again, but the phone system would not accept a voicemail and no representative answered. My case number with Mercedes-Benz is 19653254. No prior abuse, misuse, or abnormal driving conditions occurred. The vehicle was properly maintained.
NHTSA complaint #11706568 — an unverified report by a vehicle owner.
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.
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.
I am reporting a serious vehicle safety hazard caused by improper and unsafe repair work performed by USA Platinum Motor, located at 1221 California Lane #126B, Arlington, TX. I brought my 2017 Mercedes-Benz C300 in for a cold start rattle with no warning lights or prior issues. The shop diagnosed a loose timing chain and I authorized the repair. After the repairs, the vehicle was returned with critical safety defects, including a loose fuel pump, unsecured fuel line, missing bolts, and improperly reassembled engine components. Shortly after pickup, the car experienced loss of acceleration on the interstate, a strong odor of fuel, and a sudden loss of power, creating a dangerous and life-threatening situation. The vehicle had to be towed back to the shop. The manager, who is not a certified mechanic, admitted he personally “fixed” the issue by tightening the fuel pump himself. A Mercedes-Benz diagnostic inspection later confirmed multiple severe assembly errors, including missing fasteners, unsecured oil cooler, disconnected vent lines, and other safety-related defects in the fuel and cooling systems. These unsafe and negligent repairs created an extreme fire hazard, engine instability, and risk of sudden failure while driving. I am requesting a formal NHTSA investigation into this matter to ensure vehicle safety compliance and to prevent similar incidents affecting other consumers.
NHTSA complaint #11696497 — an unverified report by a vehicle owner.
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.
NHTSA complaint #11695702 — an unverified report by a vehicle owner.
My vehicle only had 31,000 miles and I experienced engine failure. I bought a new engine for 16, 500. 00 dollars. Mercedes Benz did nothing. I almost got in to several accidents because the engine completely stop on the interstate. Almost got hit by several cars. This is unacceptable.
NHTSA complaint #11695170 — an unverified report by a vehicle owner.