2020 Mercedes-Benz C 300 Problems

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.

points: ⸻ While driving, the vehicle displays the warning “Active Brake Assist Functions Limited – See Operator’s Manual.” The message appears during normal driving and does not go away. This warning indicates that the automatic emergency braking / Active Brake Assist system is limited or disabled, reducing a critical safety feature designed to help prevent or mitigate collisions. This creates a safety risk because the vehicle may not automatically brake in an emergency situation. The warning appeared suddenly while driving, with no visible obstructions, weather conditions, or damage to sensors. Restarting the vehicle does not consistently clear the message. The issue has not yet been inspected by a dealer or repair facility. The cause of the malfunction is UNKNOWN, and the vehicle is available for inspection.

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.

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.

I own a 2020 Mercedes-Benz C300 equipped with a power trunk. On July 22, 2026, I took my vehicle to Annapolis Mercedes-Benz because the power trunk was repeatedly closing on its own while people were standing in the trunk opening. I specifically reported that the trunk was unexpectedly closing while I, my child, or another individual was loading or unloading the vehicle and expressed concern that someone could be injured. The dealership kept the vehicle for several hours but advised me that no malfunction could be found. I was told the trunk had been reset and that there were no problems with the vehicle. I also provided video evidence of the trunk malfunction by text message to my service advisor. On August 2, 2026, the exact same problem occurred. While I was loading groceries into the trunk, the power trunk unexpectedly closed without warning and struck my son in the head, causing injury. This incident occurred after I had already reported the same safety concern to the dealership. I believe the power trunk is malfunctioning intermittently and presents a significant safety hazard because it can unexpectedly close on a person while the trunk is being used. I am requesting that NHTSA investigate this potential safety defect, as it may pose a risk of injury to other vehicle owners and passengers.

Automatic trunk closing mechanism caused the trunk hood to close on my head as I was putting groceries in the trunk. This has occurred several times in the past but this time it hit my head with more force. I have not brought it to a dealer and it has not been inspected by the manufacturer, police or any other entity. There was no warning or alarm before it closed. This could cause serious head injury to an individual on blood thinners.

The contact owns a 2020 Mercedes-Benz C300. The contact stated that a section of the roof near the top of the windshield, between the sunroof, had detached and flown off the vehicle while driving 30 MPH in bumper-to-bumper traffic. The driver was able to grab the portion of the rubber gasket and pulled it into the vehicle through the driver’s side front window. The roof was in three pieces. The contact turned on the hazard lights and was able to pull over safely to the side of the roadway. There were no warning lights illuminated. The contact was concerned about the failure potentially causing a road hazard under different circumstances. The vehicle was taken to an independent mechanic the next day who declined to service the vehicle and informed the contact it was an issue for the manufacturer. The contact went to a body shop and was informed that the failure was caused by a design flaw. The contact called the local dealer, who initially did not respond. The contact called the dealer again, who requested photos. The vehicle was taken to the local dealer, who declined the repair the vehicle and escalated the issue. The vehicle was not diagnosed or repaired. The manufacturer was contacted regarding the failure and opened a case, but no decision had been made regarding the repair coverage. The failure mileage was approximately 28,722.

Sunroof is not closing

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.

points: ⸻ While driving, the vehicle displays the warning “Active Brake Assist Functions Limited – See Operator’s Manual.” The message appears during normal driving and does not go away. This warning indicates that the automatic emergency braking / Active Brake Assist system is limited or disabled, reducing a critical safety feature designed to help prevent or mitigate collisions. This creates a safety risk because the vehicle may not automatically brake in an emergency situation. The warning appeared suddenly while driving, with no visible obstructions, weather conditions, or damage to sensors. Restarting the vehicle does not consistently clear the message. The issue has not yet been inspected by a dealer or repair facility. The cause of the malfunction is UNKNOWN, and the vehicle is available for inspection.

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.

The component that failed was the fuel injector and spark plug. A few months prior to this incident, I was making a left hand turn, when the accelerator completely gave out. I was making the left on a blinking yellow arrow, luckily the on coming car was not coming at me fast or I would've been in an accident due to the accelerator failing. I had to pull over, turn the car off and then back on to reset it. I was told by the dealership service center that they could not find anything and that there have been no complaints or recalls. After about 8 months of owning the vehicle, it started to have problems turning over when the engine on/off button was pressed. I was repeatedly told that they could not do anything if it did not happen in the dealership service center. This past week on 10/20/2022, while I was driving down the freeway, when I went to accelerate and at that moment the vehicle began to stutter/shake uncontrollably. After that, any time the accelerator was pressed it would shutter/shake. My vehicle was towed to a dealership. Come to find out, cylinder one was coding. They found out that the fuel injector was stuck open. According to the service advisor, that issue was causing a misfire. I was told that they replaced the fuel injector and the spark plug. According to the vehicle report I was given, 1 reman injector, 4 TS spring F In, 1 spark plug, and there was a core return (not sure what that means). The check engine light came on right away. In addition to the incidents above, I have had the forward collision alert come on when nothing is in front of me. I worry that one day it will cause my vehicle to engage the brakes when nothing is around.

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.

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.

The issue is that the trunk lid closes abruptly and unintentionally. On Saturday, February 3, 2024, as I was putting a shopping bag in the trunk of my car, the trunk lid closed abruptly without my pressing the close button and hit my forehead. The impact was such that my eyeglasses flew off my face and hit the ground. The pain was severe and two days later, I still have pain. While there was no tear to the skin, there's a bump on my forehead and is still painful. The head injuries generally do not show adverse symptoms until months after the incident. I called the Mercedes Benz corporation and after they checked the car VIN, said there had not been any recall for this specific issue. However, searching the internet, there are reports and complaints about this exact defect.

TL* THE CONTACT OWNS A 2013 MERCEDES-BENZ C300. THE CONTACT STATED THAT THE DOOR HANDLE WAS FRACTURED INTERNAL AND UNABLE TO BE OPENED FROM INSIDE OF THE VEHICLE. THE CONTACT STATED THAT HER SON WAS LOCKED INSIDE THE VEHICLE AND UNABLE TO EXIT. THE CONTACT INFORMED HER SON TO USE THE KEY FOB TO EXIT THE VEHICLE. THE VEHICLE WAS TAKEN TO AN INDEPENDENT MECHANIC AND WAS DIAGNOSED WITH A FRACTURED INTERNAL DOOR PANEL WHICH CAUSED THE DOOR HANDLE TO BECOME INOPERABLE. THE VEHICLE WAS NOT REPAIRED. THE MANUFACTURER WAS NOT CONTACTED OR INFORMED OF THE FAILURE. THE APPROXIMATE FAILURE MILEAGE WAS 108,000.

I purchased this vehicle on December 26, 2025 from an authorized Mercedes-Benz dealership. Shortly after the purchase, I discovered an issue related to the airbag system, which indicates a potential safety defect. At the time of purchase and during the test drive, the vehicle was already turned on, and no warning or disclosure was provided regarding any airbag malfunction or warning message. The issue became apparent only after the purchase. I later brought the vehicle in for repairs. While some repairs were performed, the airbag issue was not fixed and remains in the same condition as before. The dealership is now refusing to repair the airbag system at no cost and is insisting that I pay for the repair, despite the fact that this defect appeared immediately after purchase and was never disclosed to me. I believe this represents a serious safety concern, as a malfunctioning airbag system may fail to protect occupants in the event of an accident. I also believe the vehicle was sold to me with an undisclosed safety defect. I am requesting that this issue be formally reviewed and investigated.

On July 17, 2021 I was driving at the posted rate of speed down I-275 Southbound here in Michigan. All of the sudden and without warning, there was a loud explosion which happened, from as near as I can tell, in the driver's side windshield pillar, where there is an airbag. No warning lights came on, and the car did not change its driving characteristics. Only after I reached my destination and searched under the dash, and every where else (including the exterior), did I find that the plastic "cover" on the pillar is pushed away from the pillar and much more loose than the plastic cover on the passenger side. Since the incident, I have had severe tinnitus in my left ear which was about 15-18" away from it. The air bag did not deploy. I did not hit a pothole, did not hit a bump, did not hit another vehicle.

Over the past month, my 2020 Mercedes-Benz C300 has been experiencing unexpected and increasingly concerning issues with the steering. These problems began suddenly and without any prior warning signs. Initially, the steering has been making grinding sounds more usual, particularly at lower speeds and when making tight turns. Over the following weeks, the issue became more pronounced, with occasional instances of the steering wheel resisting movement or feeling delayed in its response. At times, it feels as if the power steering system is intermittently failing or underperforming. There have been no warning lights on the dashboard, and I have not been involved in any recent accidents or incidents that could have caused physical damage to the steering system. I have maintained the vehicle in accordance with the manufacturer's guidelines, including regular servicing. but there the person before me had been in a accident and it may have been the dealership i bought it off of failed to fix it

While driving on the turnpike without warning my steering locked and I lost control of my car.

BOTH the front tires in my 2020 Mercedes C300 developed sudden belt separation while driving at highway speed this past weekend. These tires were installed by Mercedes of Delray Beach Florida as part of my CPO vehicle purchase in September of 2022 and have less-than 20K miles on them. Tires are Continental ProContact size 225/45 R18 and marked M+S as well as MOE. The vehicle received a routine four-wheel alignment as part of my annual servicing in July 2025 by Mercedes of Fort Pierce, and no indication of any tire issue was mentioned. Tire pressures have been consistently checked monthly and always set cold to 37-PSI specifications. The first indication of a tire issue was a sudden vibration in the steering wheel and I thought I may have lost a wheel weight after driving thru our local car wash the day prior.

OEM tires that the Mercedes Benz dealership diagnosed as having shifted belts. 245/40 R18

points: ⸻ While driving, the vehicle displays the warning “Active Brake Assist Functions Limited – See Operator’s Manual.” The message appears during normal driving and does not go away. This warning indicates that the automatic emergency braking / Active Brake Assist system is limited or disabled, reducing a critical safety feature designed to help prevent or mitigate collisions. This creates a safety risk because the vehicle may not automatically brake in an emergency situation. The warning appeared suddenly while driving, with no visible obstructions, weather conditions, or damage to sensors. Restarting the vehicle does not consistently clear the message. The issue has not yet been inspected by a dealer or repair facility. The cause of the malfunction is UNKNOWN, and the vehicle is available for inspection.