Mileage when the problem started
Owner reports
Selected complaints filed with NHTSA by 2018 Mercedes-Benz GLC300 owners, lightly cleaned up (personal details are redacted by NHTSA).
The contact owns a 2018 Mercedes-Benz GLC300. The contact stated that while driving 65 MPH, the vehicle started to hesitate while depressing the accelerator pedal. The contact stated that the vehicle also started shaking and vibrating with the check engine warning light illuminated. The contact managed to pull the vehicle off the highway and had the vehicle towed to a dealer. The vehicle remained in the dealer's possession for several weeks before the contact was informed that it was discovered that the piston rings were burned and that the cylinder head was warped. The manufacturer was notified of the failure but had not yet receive a response. The vehicle was not repaired and remained in the possession of the dealer. The failure mileage was approximately 9,200.
I brought my vehicle in to get serviced because the check engine light came on and I was told it was CODE PRESENT P0521E71 VALVE FOR CRANK CASE VENT. HAS MALFUNCTION / BLOCKED. I was told I have warranty on it so Mercedes of Massapequa took the car to fix.I was told the part was fixed but oil was found on my engine computer from the crank case vent malfunctioning but the warranty won't cover it although it was a direct result of a part that was covered part and had caused the damage.They gave me my car back and my car is worse it has problems starting it requires multiple cranks and the air conditioner has a fuel smell when turned on and I am unable to pass my vehicle inspection because my check engine light it still on.I spoke to the corporate office and they said because I have too many miles they can't do a courtesy and honor the cost and referred me back to the dealer and the dealer …
The car does not go into drive from reverse and will sometime automatically shift itself from a low drive gear (D1) into Neutral without warning. After this happens - the car also can't get back into D1. It takes about 20 seconds for the car to shift back into a Drive gear and it will jolt into D3 violently. This has been a scary experience on many occassions - especially at red lights when this happens and we can't get the car out of neutral for some time. This was diagnosed by mercedes dealership near us as a fawlty sensor in the transmission. It is extremely expensive to fix and is specific to mercedes meaning it has to be done by a MB dealership. We applied for good will for assistance but were denied. The car has been maintained very well - this is not a maintenance issue but a specific sensor failure of a mercedes sensor in the transmission. …
I had the engine light come on and took it to the dealership. They quoted me over 8 thousand dollars to fix. I took it to a repair shop that works on luxury cars and they fixed it for less than 1000 dollars. I had to have the transducer fixed in the turbo in my engine and when they did that they found oil in the electrical harness. That was caused by the oil seperator. They told me that it was a manufacture defect that has been well documented and to take it back to Mercedees Benz. They looked and found the oil but said my car did not produce a code and could not fix it. We escalated it to corporate that reviewed my case and said they still would not fix until it produced a code. Mercedees implemented an extended warranty for my car back in 2022 for emissions. They said they would cover it if it produces a code. …
Component Failure: The vehicle is equipped with the M274 2.0L turbocharged engine, which suffered a major internal mechanical defect. An authorized Mercedes-Benz dealership diagnosed the vehicle at 79,504 miles with a malfunction in the crankcase ventilation system alongside severe internal defects, quoting a total repair estimate of $9,851 to perform extensive engine work. Safety Risk: This known manufacturing defect involves premature failure and cracking of the pistons, which poses an immediate safety hazard due to potential catastrophic engine failure and sudden, complete loss of motor power while driving at highway speeds. The manufacturer has failed to offer an extended warranty or recall for this known issue on the 2018 model year.
Vehicle stopped while driving on road. Car show "active brake assist malfunction" on the dashboard, immediately following the car will not accelerate. Shut the car off and restart, then the "check engine light" comes up. The active brake assist does not come up again, but the check engine light states on. I have taken the vehicle 5 times for this issue to the dealer, car is currently at the dealer. Reason of my report, is that I consider this situation extremely dangerous and should be investigated further. [redacted]
Complete engine failure after 55,000 miles determined that there was a broken piston #1 in the car. This required a complete engine replacement. This is a known problem by Mercedes with the engine model M274 there are numerous reports of the same problem in this engine over several models and years. The engine was 5000 miles out of warranty however this problem seems to occur in alot of vehicles from Mercedes with this engine. There is an active class action lawsuit in California regarding this. Mercedes seems to be ignoring this issue and or not dealing with it to date.
Car failed to accelerate due to faulty fuel pump, fuel tank, etc. Car stopped and died several times in the middle of heavy traffic. Mercedes Benz of West Houston, Sewell Dealership, has my car that was towed to them late afternoon on 3/5/2024. I have owned a Mercedes for over 40 years and never had this occur or be scared due to the car's lack of performance.
Error code P052E71 on a 2018 Mercedes-Benz GLC 300 4MATIC means the Positive Crankcase Ventilation (PCV) Regulator Valve Performance has a malfunction, specifically that the partial-load ventilation valve actuator is blocked. By research, i found that this is a very common problem on those engines, and no recalls from the company to fix their fault.
Vehicle is switching gears automatically from Drive to Neutral in the middle of the road, in the middle of driving, VERY dangerous situation. I cannot put in reverse sometimes it switches back to N. . It always switch his back to neutral. Thankfully no accidents. Don't know what to do?
Engine complaints in other GLC300 years
Frequently asked questions
How common are engine problems on the 2018 Mercedes-Benz GLC300?
NHTSA has 28 complaints about the engine & cooling of the 2018 Mercedes-Benz GLC300, 32% of the model year's 87 complaints.
Is there a recall for 2018 Mercedes-Benz GLC300 engine problems?
No. NHTSA lists no engine & cooling recall for the 2018 Mercedes-Benz GLC300, though it has 12 recalls for other components. If the problem is widespread, a repair may still be covered by an extended warranty or a manufacturer service bulletin — ask a dealer.
At what mileage do 2018 Mercedes-Benz GLC300 engine problems start?
Half of the complaints with a recorded mileage happened before about 6,000 miles, and 100% before 25,000 miles.
Is it dangerous?
Owners linked 0 crashes, 1 fire and 0 injuries to engine & cooling problems on this model year. If you notice symptoms, have the car checked before driving further.
Source: U.S. National Highway Traffic Safety Administration (NHTSA) — owner complaints through October 20, 2026, recalls and defect investigations; fuel economy from the EPA. Complaints are unverified reports and are not proof of a defect. How we rate model years.