2015 Mercedes-Benz C300: misfire or rough idle

Filed May 29, 2025 · Suspension, Transmission · CT

Rear-subframe corrosion at the lower-control-arm mounts has progressed to the point where both arms have play and produce loud metallic bangs while braking or turning at low speed. Two independent shops lifted the car, documented flaking rust around the bushing sleeves, and advised the subframe is structurally compromised and could let a control arm detach under load. The corroded subframe remains installed and can be inspected on request. Safety risk: a detached rear control arm would cause sudden, unpredictable steering and loss of control. The vehicle already pulls right under braking, and feels very unstable in curves Problem has been reproduced and photographed by two independent repair facilities. No manufacturer representative has inspected the vehicle so far. Additional component failures possibly linked to the same progressive chassis stress: premature wear of both front CV axles; timing-chain stretch with worn guides; slack oil-pump chain; upper & lower oil-pan gasket leaks; water-pump seepage; right engine-mount collapse; persistent misfire traced to a loose intake-hose clamp; transmission-cooler hose clip released under pressure, dumping all ATF and destroying the automatic transmission; excessive play in all four lower control-arm bushings. The transmission and the other components were replaced 1-2 months before the subframe bro History: A faint clank from the rear suspension first appeared roughly three years into ownership. Dealer service dismissed it as “normal noise,” and warranty would not cover “loud clanks,” so the issue went unaddressed. The noise has grown steadily into the current condition, suggesting long-term subframe corrosion that was never inspected or remediated. No collision, flood, or off-road use; the car has typical Northeast winter-salt exposure. The failure pattern matches subframe-corrosion cases already acknowledged by the manufacturer on this model, although this serial number is not yet included in the official campaign.

Filed Mar 31, 2023 · Engine · MD

My vehicle is a 2015 C300 AWD. One day I was driving on the highway and noticed white smoke coming out of the exhaust. The check engine light came on shortly after as I pulled over. Being that I was less than a mile from my house, I decided to go park the vehicle. I noticed that it was losing power and had problems going above 45mph. Since my vehicle had 99k miles. I took it to my indy mechanic that has worked on the vehicle since it has been out of warranty. When he diagnosed the vehicle, 48 codes came up. He suggested we change the spark plugs and coils, which we did. Didn't fix the problem. Then he suggested we change fuel injector 1, which we did. That didn't solve the problem. I decided to take it to the local Mercedes dealership where they did another diagnostic test. And like many others here, cracked piston/cylinder 1 dead. I'm looking at $18,000 in repairs. I told them no thank you. The car is now sitting in my garage. I really hope Mercedes makes this right with its customers. There is no reason why this many people should be having this exact same problem. Vehicle Symptoms: White smoke out of exhaust Check engine light on Cylinder 1 Misfire Burning Oil Causing loss of power Radio randomly shuts off & went into Anti Theft Mode

Filed Feb 28, 2023 · Engine · AZ

Driving the 2015 c300 with approx. 69k in miles down the highway and heard a pop and the check engine light came on. The next day there was a rough idle and clanging at low speeds. took to dealership and they quoted me $15k in repairs for a new engine. MB tech said the cylinder #1 is out of spec., and there is scoring on cylinder wall caused by the piston being off center and riding the cylinder wall. After doing research this is a common problem with the m274 engine. How has this not been recalled and taken care of by Mercedes?? At this point i am 'forced' to either come up with $15k for the repairs, or go to MB dealership and try to get into a new car...which i am over $12k upside down on i might add

Filed May 16, 2022 · Engine · CA

Cracked cylinder #1. Causes rough idle, loss of power and lots of white smoke out the tail pipe. This is dangerous for anyone behind the car trying to see through the smoke then loosing power and other vehicles almost hitting me. Mercedes know they are defective but because of the large cost associated with repairing them they will not fix.

Filed Jul 5, 2021 · Engine · 48,000 miles · NY

In March of 2020 I was driving home from work. I stopped at a red light. When it turned green, I proceeded to step on the gas. My car started making noises and shaking as I drove. My check engine light came on. I was able to pull over without incident. My vehicle has under 48k miles on it! I had it towed to a Firestone facility by my house. They replaced spark plugs and ignition coil 1 and 2. They said it was still severely misfiring. Cylinder 1 must have internal damage and should be towed to the dealer. They gave me a spark plug they removed that had significant damage to the top part. They said something must have impacted it with significant force. I then had the vehicle towed to a Mercedes Benz Dealership. They said they inspected with a scope and found piston material missing, can see ring exposed and have damage to cylinder wall. Will need to replace engine, turbo charger, cat converter intake manifold to repair. They wanted $18k to repair. I did some research and found out that the 2015 Mercedes C class was the first year they switched from 6 cylinder to 4 cylinder turbo charge engine. These models have had a significant amount of engine problems and failures, the manufacturer is aware of. Many of these occurred in cylinder 1 along with wrist pins issues and others. I found my situation wasn't unique. I then filed a complaint with The BBB in Georgia. MBUSA offered me $3k towards the repair or purchase of a new vehicle. I declined the offer. I only wanted my vehicle repaired. I wasn't alone in this situation. These issues are easily found online. My vehicle has since been sitting in my driveway for almost a year and a half. I've been making my monthly car and insurance payments on a vehicle I can't drive. I recently went to the Mercedes dealership and they will give me $5k for the vehicle towards a trade, leaving me with $15k negative equity towards the purchase of a vehicle. Mercedes should stand behind their products and do the right thing