Mercedes-Benz C300 knocking problems

Filed Aug 7, 2026 · Engine · 88,000 miles · WI

The contact owns a 2021 Mercedes-Benz C 300. The contact stated that while depressing the accelerator pedal, there was a loud knocking sound coming from the engine compartment while accelerating. There were no warning lights illuminated. The vehicle was taken to the dealer to be diagnosed, and it was determined that the spawn rod was fractured, causing engine failure. The contact was informed that the engine needed to be replaced. The vehicle was not repaired. The contact stated that the engine was previously repaired because of the head gasket failure in 2024. The manufacturer was informed of the issue, and a case was opened. The failure mileage was approximately 88,000.

Filed Apr 9, 2024 · Suspension · NH

Recently I was driving and heard a knocking/creaking noise in the left rear. When braking I felt as though I was going to lose control of the vehicle...vehicle appeared to fishtail and pull to the left. I first noticed it on [XXX] when I was driving on the highway in excess of 60 MPH. On [XXX] I brought it to my mechanic (Genesee Auto Repair, 40 Liberty Street, Salem, NH (603)898-1899) and my mechanic informed me that the left rear subframe had rotted out and told me that I should not be driving the car. There were no warning lamps or messages indicating there was a problem. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Feb 22, 2024 · Brakes, Suspension · IL

While I was driving my 2012 MB C300 4Matic Sport Sedan in Nov', 2023 with history of regular maintenance, noticed a pretty load knocking noise, shudder and drifting to left a bit when it brakes from the driver's rear side especially on the highways. I took it to our local mechanic who was horrified to report that the sub frame was broken and completely rotten out too specifically rust issue with the rear suspension-rear subframe. He gets other German Cars like BMW & Audi even older and more miles in Chicago but none have rusted so much as these MB C-Class cars. Knowing the Dealers wont accept it a manufacturing defect, he was planning to repair it (no chance of wielding that thin metal sheet as the likelihood of breaking it is high). I was surprised to see 2010 Chevy Impala having a much more robust under the cover protection and no rusting with 115k miles. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Jan 28, 2024 · Electrical, Engine · CA

First day leasing the vehicle within 6 hours lights malfunction and malfunction warning on dash to seek workshop, vehicle was taken for inspection to original dealer (Mercedes Benz of Bakersfield). During inspection I added additional concerning complaints about passenger door not closing correctly/wind noise seeping through when closed, and hood not closing promptly. One month into leasing vehicle passenger window malfunction, took for inspection and repair to original dealer (MBofBakersfield). Concerned with caution for me, my family, and friends when in that vehicle for giving faulty signs so early. One year into leasing vehicle check coolant warning on dash, took for inspection to original dealer. I am now more concerned as it went form electrical to coolant components losing coolant with no reasoning from original dealer service other then a top off. Vehicle drive is rough. 1 year and 6 months into leasing vehicle, again check coolant warning on dash. Took in for inspection, gave no reasoning from original dealer service dept, other then a top off done. Vehicle drives rough. While driving 70mph, a vehicle behind was approaching quick when I went to excel to merge vehicle seemed to be slipping in gear/slow down. No warning lamps on, Quickly decided/managed to merged to next lane so vehicle behind didn’t hit us as we were slowing down With 2 children in the back seat. decided to exit to nearest exit to pull off as it felt unsafe to drive, as exiting and slowing down vehicle began to shake, knock, and make loud bangs. Managed to pull over, and check dash for messages for any type of warnings. No warning lamps, but many symptoms of a faulty unsafe vehicle. Had vehicle towed to original dealer service for diagnosis and report the unsafety incident that occurred with absolutely no warning lamps. Inspection lead to repair of engine but nothing done about no warning lamps/electrical system

Filed Jun 21, 2023 · Fuel system · KY

My check engine light came on approximately one month ago. Once tested it indicated a fuel vapor leak. I pulled out of a driveway and a large stream of fuel spilled all over the roadway. Approximately 7 feet in length about 5 inches in width was on the road. I took it to a Mercedes repair shop and they informed me I had a fuel leak and that it was not safe to drive. There was corrosion and rust forming on the tank which seems very odd since the car is garage kept and we don't get much snow in Kentucky. My daughter rides in this car with me and they told me it is very dangerous and needs repaired. If I was to drive over a cigarette we could essentially blow up. I had a second shop look at it and they also informed me I had a fuel leak and would need to replace the fuel tank. I was told there was a recall on some models of Mercedes for this issue but can't seem to find one on my year make and model. Please help with this matter so my daughter and I can remain safe as well as others around us. Seems like we are in a ticking time bomb.

Filed Apr 18, 2023 · Suspension · NC

The rear subframe rusted prematurely and broke off important mounts for the suspension and steering. I was driving and had to hard brake. This cause the back end of the car to swerve and almost lose control. I then heard a knocking sound when I pressed the brakes, prompting me to take it into the shop. There I was informed the the subframe was rusted and the vehicle wasn’t safe to drive. I filed a claim with my insurance, but they said it’s wear and tear.

Filed Mar 3, 2023 · Body, Suspension · WA

The subframe assembly on my car is defective, as I learned today from my mechanic. This issue is known for my model of car and widely reported online. The mechanic says they have seen this issue before. I heard a strange noise while driving so I took the car to the shop after 60 days of enduring the sound. The shop immediately deemed the car unfit for driving and unsafe. In their words, if I had hit one bad pothole, the wheels could have come off the back of my car, and my gas tank could have been punctured, leading to a potentially catastrophic accident. I am lucky to have gotten this defective part identified before being injured, and others need to be protected from this outcome before a serious injury occurs. As of now this has only been inspected by the shop doing the fix. People online have indicated that Mercedes will not fix the problem free of charge - and in fact they charge a premium to other places to replace this faulty subframe. There were zero warning indicators of this dangerous issue - the car drove completely normally aside from an infrequent knocking sound that would occur every 5-10 minutes under normal city driving conditions.

Filed Jun 22, 2022 · Suspension · PA

My 2014 Mercedes C300 4matic currently has a rusted through rear subframe. I know this has been reported to your Bureau numerous times by various people. This affects all 2008-2014 C Class and E Class Mercedes (as I used to work for a Mercedes dealer). Mercedes is trying to avoid liability at the sheer cost and man hours required to replace these parts. This is a MAJOR safety hazard, and has caused numerous drivers to lose control of their vehicle when they do in fact break off at one of the weld joints. The car is 8 years old with approximately 90k miles. This is a STRUCTURAL part of the car, and should never have to be replaced. Subaru dealt with suspension recalls on their vehicles, and I believe Mercedes should be reliable as well. Thousands of these cars are a ticking time bombs on the road. This issue was confirmed by my personal mechanic, and he stated this will not pass the next inspection (luckily I have 6 months left).

Filed May 4, 2022 · Body · 139,000 miles · DE

The contact owns a 2011 Mercedes-Benz C300. The contact indicated that while driving at various speeds, a knocking noise was present coming from the rear of the vehicle. Additionally, while abruptly braking the vehicle would pull to the left. The vehicle was taken to the local dealer who diagnosed that the rear subframe was fractured. The cause of the subframe failure was not determined and no further information was available. The vehicle was not yet repaired. The manufacturer was not yet notified of the failure. The approximate failure mileage was 139,000.

Filed Mar 21, 2022 · Suspension · PA

While traveling on the interstate @ 60 MPH, I loud knock was heard in the right rear. When brakes were applied, the vehicle pulled to the left, severely. Vehicle was taken to a mechanic on this date after making an appointment. Photos included show the issue as to why this occurred. The 'cradle' of the rear suspension on both, the left and right sides were completely rusted through. The vehicle is a 2011 Mercedes-Benz C-300, with 63,000 miles. After researching this on line, it appears this is an on-going issue with this year along with other years. This, is huge safety issue and the results could be catastrophic to the occupants and or other operators.