Hello everyone, I frequent these forums but haven't had to post anything until now. I need some advice as I don't know what to do with my issue.

I own a 2015 c300, it's CPO but still also under original factory warranty (until next month). For about 8 months now I been complaining to the dealership about hard shifts, on one occasion it even shook the car like I ran over something. I had no proof that I didn't run over anything but I am pretty certain it was the transmission. Every time I bring it to the dealership they drive it around, they don't feel anything and there is no codes, they always give me the "it's cold excuse".

Fast forward up to last weekend, I had my family in the car going on a trip out of state. Two hours into drive I was about to go through ezpass toll, I slow down a bit as I go through the toll lane, once pass it I hit the gas to come back up to speed, and the car shook as if it was stalling about 5 times, (picture going over 5 small speed bumps in succession) it was hard enough to wake my kid. Then again about 30 mins later it did a really hard shift as I was trying to overpass someone at highway speed, I'm not talking like a little hard, but like I ran over something. And as luck would have it, it did it again about an hour later when I slowed down because someone got into my lane, then I tried to pickup speed, and the car was shaking as if it couldn't get into gear, it only stopped once I let go of the gas and press on it again. At this point I am really scared, I have my 3 year old in the car and I'm afraid that this car's transmission will lock up on me on the highway, it really put a damper on the whole trip. Thankfully it didn't happen again. Although after those few episodes I was driving like a grandma because I didn't want anything happening with my family in the car.

I setup an appointment with a foreman this time to drive it with them. I was really hoping for some codes in the system though, as like I said, it doesn't happen on demand which is why every time they drive it, they don't feel anything. And ofcourse nothing happens with the foreman drive.

Without been able to replicate it or codes they keep telling me that they can't do anything. But after last weeks episode on the highway I am really scared to drive this car on the highway, I feel like it's an accident waiting to happen; I feel like the dealership is not doing much to try to figure out what's wrong with this transmission other than driving it and seeing if they can replicate it. I expected more from Mercedes, and I don't know how else to get some results.

Sorry for for the long post.

 

This sounds identical to the symptoms I recently had with my 2015 C300 - only 61,000 kms.

The car would shake under load when accelerating. I also thought it might be the transmission but the root cause was the motor. After much escalation and arguing with MB, they are replacing the motor under warranty.

Suggest you escalate your issue so it’s diagnosed and repaired under warranty. MB seems to want to avoid repairing product defects - you'll need To be a squeaky wheel. 😉

 

I had something similar with my transmission. It would happen only when I hit the gas hard, especially in sport+.

Changing the water pump fixed the issue. It was the turbo or inter cooler overheating from what I understood.

Does you radiator fan come on often?

 

I have not noticed the radiator fan go on, but I'll keep an eye out for that.

I called customer service and also talked to the service manager. They had the car for 2 days now which is longer than they had it on the previous visits, so I'm hoping that means they are actually taking my concern seriously now, we'll see what they say soon.

i have been searching online for any mention of this issue, searching for "transmission jerking" actually gives me some posts of people who sound like they had similar issues. like this one:
https://mbworld.org/forums/c-class-w...elerating.html

so it's definitely an issue they should know about by now.

 

Update.

The dealership called yesterday, said that they drove it around for a couple of days and couldn't replicate it to come pick up the car. (Even though I told them it doesn't happen all the time, I don't know why they keep insisting that if they can't replicate it it's not an issue).

i called customer service explained my situation, they informed me to tell the dealer to escalate the problem if they can't figure it out. So I did just that when I went to pick up the car. The service manager told me to hold on a sec and went back into the work area. A few mins later came back with someone who is their most senior person there so I can drive it with him. Again I told them, driving it is not going to do any good, it doesn't happen all the time, and the few times it happens months have gone by between episodes. So he asked me to just explain to him what I was doing when the problem occurred, (mind you I already explained to the advisor so clearly the messages are not passed on). Immediately he says I think I know what it is "it's most likely a bad crackshaft sensor", and asked to keep the car a few more days.

so let's hope that is the issue, from the post I posted above it seems that was the same solution for another forum member.

now I don't understand why if I have brought the car in 3 times, no one bothered to check with the more senior technicians to see what they think, instead of just dismissing my concern. This guy indicated he didn't even know my car was there for that issue and that he has dealt with similar issues like this before.

 

Was the crankshaft sensor the root cause of the issue in the end? Facing similar problems myself