2018 Mercedes-Benz C300 Problems

What owners report

Owners of this model year most often describe a check engine light with a P052E code, which points to the crankcase ventilation valve. The next most common group is roof panel, sunroof and rear glass problems, reported at about 45,000 to 109,000 miles where mileage is stated. Some of these roof and glass complaints describe sudden loosening while driving, while the valve complaints usually begin with a warning light and a fault code.

1. 1
   Engine

   Check engine light with P052E crankcase valve code

   • 32 complaints (32%)
   • typically at 5.9 yrs old
   • filed 2022–2026

   Owners describe a check engine light with code P052E, which refers to the positive crankcase ventilation regulator valve. Some report oil leaks or oil burning, and others say they were told the problem could lead to stalling. According to the complaints, the dealer said the valve needed replacing, and some owners called the repair costly and believed a recall should be issued. Narratives mention mileage from about 33,000 to 79,000 miles, and an owner notes the problem appeared soon after the warranty ended.

   What to check: Ask whether the crankcase ventilation valve has already been replaced and request the repair records. Check for stored P052E codes with an OBD-II reader, since an owner describes the problem returning after a repair.

   2 excerpts from owner complaints in NHTSA records

   “My c300 2018 only has 50k and suddenly the engine light is on, when I check it shows that I need the Positive Crankcase ventilation valve replaced. it cost $2300. As I know a lot of people who own Mercedes have the same problem. Three mechanics claim it on almost all C, CLA, and GLA models. Please make Mercedes recall it finally.”

   NHTSA complaint #11533877, filed 2023-07

   “Engine light P052E, This seems to be a common problem with the C300.My concern is that Mercedes Benz hasn’t address the common issue. I own the car less than a year got it from Mercedes dealership and to be honest I expect Mercedes Benz to be better than the this to it customers”

   NHTSA complaint #11508602, filed 2023-02
2. 2
   Body and structure

   Roof panel or rear glass detaching, sunroof sticking

   • 10 complaints (10%)
   • median 60,000 mi at 7.2 yrs old (6 state mileage, few)
   • filed 2022–2026

   Owners describe the front roof panel, the panoramic sunroof or the rear window coming loose, or a sunroof that sticks or will not close fully. In some complaints the panel or glass separated while driving, and water entered the cabin; an owner links that water to electrical faults. Some owners say the dealer did not diagnose or repair the problem, and that their VIN was not covered by the related recall. Where mileage is stated, these complaints fall between about 45,000 and 109,000 miles, and some describe the panel or glass coming loose at highway speed.

   Recall 23V854000Recall 18V608000

   What to check: Ask the dealer to check the VIN for open recalls on the roof panel and rear window bonding, and confirm whether those repairs were completed. Test the sunroof through a full open and close cycle, and look for water staining or dampness around the headliner and rear window.

   2 excerpts from owner complaints in NHTSA records

   “The sunroof on the vehicle jams and either stays partially open or won’t close in the rear completely. I finally got it to close but it will not open again. I know multiple mercedes owners who have this issue with the sunroof and if the sunroof will continue to not lock properly this could be a hazard on the highway if the brackets were to break and the glass slides off.”

   NHTSA complaint #11446466, filed 2022-01

   “The contact owns a 2018 Mercedes-Benz C300. The contact stated that while driving at an undisclosed speed, the rear window glass which was not properly bonded had become loosened. The vehicle was not diagnosed or repaired. The VIN was not included in NHTSA Campaign Number: 18V608000 (VISIBILITY). The manufacturer was not notified of the failure. The failure mileage was 50,000.”

   NHTSA complaint #11617349, filed 2024-09, 50,000 miles
3. 3
   Electrical system

   Recall repairs delayed or not clearing the warning

   • 8 complaints (8%)
   • median 47,500 mi at 3.0 yrs old (2 state mileage, few)
   • 1 mention a crash, fire or injury
   • filed 2019–2023

   Owners describe an SOS not-active message or an airbag warning that appeared again after a recall repair. Some report that the recall part was not available for a long time. An owner says the dealer declined to perform an over-the-air recall remedy, and another says the SOS fault remained after repeated dealer visits. Mileage in these complaints ranges from about 10,000 to 85,000 miles, and in some complaints the warning returned after a repair had already been done.

   Recall 21V058000Recall 22V365000Recall 18V8380001 related service bulletin

   What to check: Ask for the recall completion records and whether the SOS and airbag warnings were checked after each repair. Start the car and confirm that no SOS or airbag warning remains on the instrument cluster during a test drive.

   2 excerpts from owner complaints in NHTSA records

   “To Whom It May Concern, I bought this certified preowned Mercedes Benz, and the recall is open. I have taken the car to the dealership, they deny me from service because its an over the air recall. The Mercedes Benz website clearly states on their letter for consumer that the remedy for this recall can be taken care at the dealership free of charge or an over the air update. Its July and I got the car back in February.”

   NHTSA complaint #11423935, filed 2021-07

   “The contact owns a 2018 Mercedes-Benz C300. The contact stated that after starting the vehicle, the S.O.S. Not Active message displayed. The contact was concerned that in the event of an emergency, the emergency services function would be inoperable. The vehicle had previously been serviced under NHTSA Campaign Number: 21V058000 (Electrical System, Communication) however, the failure recurred. The dealer was made aware of the failure; however, the vehicle was not diagnosed or repaired. The manufacturer was not made aware of the failure. …”

   NHTSA complaint #11511208, filed 2023-03, 85,000 miles
4. 4
   Engine

   Cracked piston and exhaust smoke

   • 5 complaints (5%)
   • median 58,000 mi at 4.3 yrs old (2 state mileage, few)
   • filed 2022–2024

   Owners describe smoke from the exhaust, rough vibration and loss of power, and in some cases a cracked or damaged piston that required engine repair. An owner says the dealer could not explain why the piston cracked despite regular oil changes, and another says an engine rebuild was needed at roughly 90,000 miles. In some complaints the car was towed to the dealer, where the complaint says the smoke was not diagnosed. Mileage in these complaints ranges from about 54,000 to 90,000 miles.

   What to check: Ask for the oil change and service history, and whether an engine inspection was done after any smoke or piston-related repair. Start the engine cold and check the exhaust for smoke during a test drive, and watch for any check engine light.

   2 excerpts from owner complaints in NHTSA records

   “CYLINDER 1 SPARK PLUGS IS DAMAGED DUE TO PISTON DAMAGE, HOLE IN PISTON. IF EXTRA DAMAGE IS FOUND ON TEAR DOWN, COMPLETE ENGINE REPLACEMENT. This is direct from the repair facilities reports. While driving my 2018 C-300 there was smoking out of tail pipe, a rough vibration, hard to control the vehicle and it was starting to lose power. Not a good situation, had to pull over and have vehicle towed to the dealership. Worst part is this is a vehicle used to transport my 5 children to and from school and activities. …”

   NHTSA complaint #11446178, filed 2022-01, 62,000 miles

   “CRACKED PISTON AT 68K MILES The vehicle is very well maintained, only 68k miles, has had every oil change, only takes premium gas. I was driving it when the check engine light went on and the vehicle began shaking violently. After towing the vehicle to the Mercedes Benz dealership, they informed me that the piston cracked and they could not articulate a reason why this would happen.”

   NHTSA complaint #11478301, filed 2022-08
5. 5
   Forward collision avoidance

   Unexpected braking and brake system warnings

   • 7 complaints (7%)
   • median 16,000 mi at 2.2 yrs old (5 state mileage, few)
   • 2 mention a crash, fire or injury
   • filed 2018–2025

   Owners describe the car braking hard without warning at highway speed, and an ABS warning light that came back after the dealer's repair. A separate complaint says the automatic emergency braking did not work as the owner's manual describes. In a complaint the brake pedal dropped after a dealer service visit, and the owner was told a brake line had rusted. Mileage in these complaints ranges from very low to about 75,000 miles.

   What to check: Ask the dealer to scan for stored ABS and brake codes, and check the brake lines and fluid for leaks or rust during an inspection. Test the automatic braking and collision warning features on a test drive, and ask whether any open recalls or service bulletins cover the braking system.

   2 excerpts from owner complaints in NHTSA records

   “I brought my vehicle to mercedes benz for a rear tail light recall. When I picked up my vehicle the brake pedal went to the floor. Note: this was not happening prior to me dropping the car off to the dealer. The service manager drove my car back to the mechanic. I was then told that, ironically, the brake line rusted (metal line) out causing the brake fluid to leak out. Also, passenger front seat sensor went. Seat will not move back or forward.”

   NHTSA complaint #11102627, filed 2018-06, 75,000 miles

   “Forward collison system ($1700 option) aeb, does not work as described in mb literature or website. In my opinion, the forward collision avoidance system (aeb) in my 7 mo. Old 2018 mercedes C300 simply does not work. I special ordered the car with the 997 pkg that includes, driver assistance, bas+, and distronic the mb manual states: 'if active brake assist detects that there is a risk of collision, you will be warned visually and acoustically. …”

   NHTSA complaint #11163276, filed 2018-12, 5,000 miles

Buying note. For someone considering this model year, confirm whether the crankcase valve has already been replaced and check that the roof panel, sunroof and rear glass are firmly attached. Ask for recall and communication module status before buying, since some complaints describe long waits for recall parts.

Summary written with AI from a sample of 60 NHTSA complaints for this model year (picked at random, with complaints that state a mileage and recent ones taken first), then checked automatically against the source records. Where a problem shows a complaint count, every complaint for this model year was matched with fixed keyword rules (written with AI and tested against the sample), and the mileage, age and repair figures are calculated from those complaints; owners' figures are as stated, not verified. Other counts refer to the sample. The excerpts come from NHTSA's public complaint records and are unverified; capitalisation is normalised, NHTSA staff notes are removed, and shortened text ends with “…”. Something wrong? Request a correction.