2017 Mercedes-Benz C300 Problems

What owners report

Owners of this model year most often report engine and emissions-related problems — rough running, stalling and a recurring check-engine code for the crankcase ventilation valve — along with seat belts that do not retract and a panoramic roof glass panel that has shattered while driving. Many reports arrive at low to moderate mileage, and a number describe symptoms that begin gradually (vibration, rough idle) before the vehicle stalls or loses power. Several complaints also describe a fuel smell or leak in the engine bay, sometimes noticed only in cold weather or shortly after a cold start.

1. 1
   Body and structure

   Panoramic sunroof glass shattering or roof panel detaching

   • 32 complaints (15%)
   • median 41,350 mi at 5.8 yrs old (14 state mileage)
   • 4 mention a crash, fire or injury
   • filed 2016–2026

   Complaints describe a loud pop or bang followed by the sunroof glass breaking and glass falling into the cabin, sometimes at highway speed and with the shade closed. Other owners report the front roof panel between the windshield and sunroof coming loose and flying off while driving. Dealers are described as attributing the glass breakage to road debris, and some owners say their vehicle was not covered by the related recall. Reported across a wide range, from around 9,000 to over 100,000 miles, typically at highway speed.

   Recall 23V854000Recall 21V197000

   What to check: Inspect the sunroof glass for chips, star cracks or unusual wear and check the front roof panel seam for looseness or prior repair. Ask whether recalls 21V197000 and 23V854000 were completed.

   2 excerpts from owner complaints in NHTSA records

   “In late october 2019, I was driving on the freeway at 70 MPH. My panoramic sunroof suddenly blow up with a loud sound. Mercedes claimed that a rock or someone shot bbgun at my car. However, I read from multiple sources that this happen often with the mercedes's panoramic roof. Lucky for me, my family was not in the car at the time.”

   NHTSA complaint #11297509, filed 2020-01, 41,000 miles

   “Sunroof explosion took place in transit to delivery to my home in centerville, ohio from houston, texas. It was stationary inside of enclosed transit vehicle.”

   NHTSA complaint #10934527, filed 2016-12, 5 miles
2. 2
   Seat belts

   Seat belts that do not retract or latch

   • 20 complaints (9%)
   • median 20,000 mi at 4.0 yrs old (12 state mileage)
   • 2 mention a crash, fire or injury
   • filed 2017–2025

   Owners report front and rear seat belts that fail to retract fully after unbuckling, leaving the belt slack or fallen on the floor, and in some cases a belt that will not latch into the buckle or becomes stuck in the retracted position. Complaints describe dealers replacing the latch or belt assembly, and several owners say the problem returned after a recall repair had been performed. Reported from a few thousand miles up to about 67,000 miles, on both front and rear seating positions.

   Recall 21V032000Recall 17V251000

   What to check: Buckle and unbuckle each belt, including the rear ones, and confirm each retracts fully and latches firmly. Ask whether recall 21V032000 has been completed and whether any belt parts were replaced afterward.

   2 excerpts from owner complaints in NHTSA records

   “Rear driver side seat belt not locking and can not depress unlocking button. Doesn't lock before starting nor after car is started and driving. Just purchased car 4 months ago back seat never used.”

   NHTSA complaint #11386566, filed 2021-01, 22,000 miles

   “2017 Mercedes-Benz C300 coupe. Seatbelt pre-tensioner , part of mercedes' pre-safe feature that tightens the seatbelt to remove slack when you click the seatbelt in, doesn't always work.”

   NHTSA complaint #11030383, filed 2017-09, 100 miles
3. 3
   Engine

   Rough running, vibration and stalling

   • 15 complaints (7%)
   • median 32,825 mi at 3.7 yrs old (8 state mileage, few)
   • filed 2017–2024

   Complaints describe vibration and shaking at idle that spreads to acceleration, slow or hesitant acceleration, and occasional stalling at stops or while driving. Several owners say a dealer replaced a piston or told them the vibration was normal for the engine, and others report repeated visits without a stored fault code. Some reports tie the stalling to battery cable or transmission/powertrain software work that did not resolve it. Reported from roughly 28,000 to 80,000 miles, often appearing first as a vibration at idle.

   Recall 17V1140001 related service bulletin

   What to check: Drive the car from cold and let it idle; feel for vibration through the seat and wheel, and ask for any stored engine or transmission fault codes. Ask whether a piston or PCV-related repair has already been done.

   2 excerpts from owner complaints in NHTSA records

   “When the car is in the a feature, where it turns on and off when not in motion, it gets stuck in that mode as if a magnet is holding it in that position. It will not move, it stalls. I turn it off and turn it back on and sometimes it still will not move, sometimes, it will not turn back on. This has happened on several different occasions. Once, I pulled to the side of my mailbox to pick up mail, and another occasion I pulled into my garage, and it stopped, and would not turn on. …”

   NHTSA complaint #11402743, filed 2021-03, 36,000 miles

   “When idling at the light. The car would shut itself off. All the warning lights will come on. I then have to restart the car with the push start to reset it. Then it'll work fine. I have been to mercedes dealership in new rochelle for four times about this issue. They changed the battery the first time. Two days later the situation occurred again. Then the second and third time they gave me back the car and said they didn't see anything wrong because no codes popped up. Both times I took the car back and the situation occurred again. …”

   NHTSA complaint #11197127, filed 2019-04, 29,000 miles
4. 4
   Fuel system

   Fuel smell or fuel leak in engine compartment

   • 22 complaints (10%)
   • median 55,000 mi at 4.2 yrs old (6 state mileage, few)
   • 1 mention a crash, fire or injury
   • filed 2019–2026

   Owners report a strong fuel or exhaust smell entering the cabin, often after a cold start or when the heater is on, and in some cases a visible leak where the high-pressure fuel line is crimped near the pump. One complaint describes smoke and flames from the engine bay traced by the dealer to a leaking fuel line. Repairs described include replacing a fuel hose or tightening a hose clip. Mostly reported between about 15,000 and 65,000 miles, often noticed in cold weather or right after starting.

   What to check: Smell the engine bay and cabin after a cold start and look for damp or stained areas around the fuel lines near the high-pressure pump. Ask whether any fuel line or hose has been replaced.

   2 excerpts from owner complaints in NHTSA records

   “A fuel line in the engine compartment just above the skid plate on the drives side just right of the front wheel well leaks fuel where the line is crimped coming from the high pressure fuel pump. Fuel collects on the skid plate and when a stop at idea produces a strong fuel smell in the cabin of the car”

   NHTSA complaint #11396042, filed 2021-02, 47,000 miles

   “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. …”

   NHTSA complaint #11738037, filed 2026-05, 65,422 miles
5. 5
   Engine

   Crankcase ventilation (PCV) valve fault, code P052E

   • 60 complaints (28%)
   • median 53,000 mi at 6.9 yrs old (1 states mileage, few)
   • owner-quoted repair $2,000 (median of 10 quotes)
   • filed 2022–2026

   Owners report a check-engine light with code P052E, described by mechanics as a crankcase ventilation regulator valve performance fault, sometimes with rough running. Complaints describe quotes of roughly a few thousand dollars for the repair and say the code returned after the valve was replaced. Some owners report the dealer declined to cover it under emissions warranty. Reported from around 15,000 to 100,000 miles, with several reports in the 50,000-60,000 mile range.

   What to check: Ask for a scan of stored codes and whether the PCV regulator valve has been replaced. Confirm the check-engine light is off before and after a test drive.

   An excerpt from owner complaints in NHTSA records

   “P052E Positive Crankcase Ventilation Regulator Valve Performance this is a common issue with Mercedes as lots of car are affected by this and this should be covered under emission but lots of dealership are declining saying it’s not covered under emission warranty but this code cause pollution and this part is so expensive to fix and I paid 2k to fix it last year and that same code came again. We can’t keep paying 2k plus for something Mercedes fault design Please help us and make Mercedes Recall this Part”

   NHTSA complaint #11577903, filed 2024-03

Buying note. Check that the seat belt and roof recalls have been completed, then take a cold-start test drive to listen for vibration, watch for a check-engine light and smell for fuel. Ask for service records showing whether the PCV valve, piston or fuel-line repairs have already been done, since several owners report repeat visits for the same symptoms.

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.