Hi Everyone!

New to the forums and hoping I could get some insight on some transmission issues I’m experiencing. I had a 2013 and 2015 C300 and both don’t downshift as hard as this car. Downshifting to a stop from 4th to 2nd are noticeable. Almost as if you were driving stick or something. Only when the engine is warm. Mornings are great for the first 5 minutes. I’ve seen forums on the older c class models and a few other models in between. Given this is a 9 speed transmission I’m wonder what in the world is going on and if anyone else is experiencing the rough downshifting on the new transmissions. Car has 1200 miles. I brought it to the dealer at 200 and nothing was found after 20 miles of driving. Given the it’s a learning transmission excuse. Scheduling a follow up with the foreman. I’ve seen others talk about replacing the transmission valve. Any thoughts? I love the car but damn it’s awful to drive on the streets.

 

Maybe if you reset your transmission TCU it will fix the issue you can do it by your self search for resetting the transmission .

 

Thanks for the tip. I could be wrong but I tried this a few times and it didn’t work on my vehicle. Not sure if it works on the 19 models. I know it worked on the 13 and 15.

 

Just have them reinstall the tranny software. Even though no hard shifts may show up, I’m pretty sure it will cure you’re problem.

 

I’ve been driving the 19 for a few days now, the 9 speed transmission with the 19 engine does feel more “rough” than the previous 7 speed. Although I can see the highway mpg being better. It just revs higher, even in eco mode.

 

I have the same issue with my 2020 9-speed C300. The downshifting especially when stopping or slowing down to a low speed is quite harsh and noticeable, with a mileage of only 4000 kms

 

I don't understand how the "adaptations" work and why they seem to adapt poorly to my extremely light driving style, but I have had this problem on every Mercedes I have owned within 10-20 miles of having the dealer reset the adaptations. I've had a 2008 C280, 2014 C250, and a 2018 C300 (all with different transmissions 7g/7g+/9g). I thought when I got the 2018 with the 9g that things were better but it just takes a tad longer to exhibit poor shifting after being reset. The Throttle Control Unit reset does help, but as you said, it is may not applicable to the 2019. I drive 95% or more in the city and in the 2018 it is unlivable. I won't be buying another - I have let myself be fooled by the Mercedes brand image twice, but will not again (that 2008 C280 was awesome but did jolt on the downshift to 2nd and 1st, build quality went way downhill starting with the W204 and the W205 is even worse). There is only so much software can make up for when the "hardware" is poorly designed and cheaply built.

In my 2018 the dealer replaced the valve body, an extremely extensive repair which did absolutely nothing. After I got it back it was just like having the adaptations reset, it shifted wonderfully for a few days and then back to the same slow and jerky behavior. The transmission related software has been updated twice. There is no further resolution the dealer can/will provide.

Had I paid more attention to how poorly made the W205 is compared to previous generations I wouldn't have bought one. Almost all interior trim pieces creak with the slightest pressure. I've had the seat bottom replaced because there were huge divots where my butt cheeks sat on the seat (I weight 135 pounds and have no butt!) after only owning for 8 months and the new one is now just as bad another year later. I cannot count how many times the brake pads and rotors have been replaced (both front and rear), they begin squeaking every 3-4k miles and there is always an "updated set" from Mercedes which is supposed to resolve the problem. The valve body was replaced, transmission software updated twice, adaptations reset 3 or 4 times now and the transmission still shifts poorly with no further resolution offered from MB or the dealer. Lots of weird configuration issues with the infotainment system, like the radio Preset View option constantly becoming unchecked when switching between Car Play and the radio. For a ~$50k vehicle the quality is extremely poor. I've learned many lessons with this Benz and got over my brand loyalty to realize there are much better made vehicles out there.

 

* 2nd gear Gremlins here, JOY!

 

I have rough shifting in and out of 5th in C. Mostly when I am slowing down to stop at a light.At first I thought it was the brakes. The car will jerk from 6 to 5. It's annoying. I did the tcu reset, nothing changed.

 

Just purchased a 2021 that has 200 miles on it with rough downshifts from 4th to 3rd gear. Does the ECU reset work on newer models?

 

My 2016 C300 downshifts hard from 5th to 4th when cold. I've learned to let it warm up when it's below 45 degrees and I don't let it shift higher than 4th gear for the first mile or two and it doesn't downshift hard like it does when cold.

 

I had this issue on my 2015 W205. Always into and out of third gear. Felt like the gear was snatching.
Mercedes had to change the transmission oil, update the transmission software and retrain the timing of the gear change.
at first it came back and they had to retrain the timing a couple of times. I then took it to a different dealer who realized the first dealer didn’t fill up the transmission oil fully (only about 50%...)
so check the tranny oil amount and software and you should be good to go

 

Bassam A Yaseen, are you an expert in C300 9 speed ?

 

Harsh downshifting is typical for this transmission, to smooth it out you can request the dealership to do a manual adaptation, it is time consuming so not all dealerships are willing to help out.

 

The 9G transmission adaptation is quite simple and straightforward, but requires the workshop to have xentry or professional advanced OBD diagnostics (like the Autel MaxiCOM MK908Pro).

 

Hmmm, thanks for sharing this screenshot. Is this the simpler/faster version of the manual adaptation or is this the actual full manual adaptation because I heard manual adaptations take a long time, like an hour or so, like is there a version of which you actually drive it instead of just standing still, that might take longer?

 

not sure if the long tedious process was on the earlier transmission versions (7G and older), the only adaptation i found through xentry for my 9G for this standstill adaptation. I had to engage into Drive mode, while stepping fully on the brake pedal i had to also floor the accel pedal (kickdown).

Quite scary doing this the first time.... as the gears shift you can feel the car wanting to launch forward...... LOL

 

Thanks again for your insight on this, there is no driving on the road adaptation as an option then (at least not anymore for the 9G) ? That is strange though if it just takes a couple of minutes like it mentions there, why are dealerships so reluctant to help customers out with this especially how much easier is it to do this and see if it helps the customer instead of replacing components etc.? I mean for example installing a TCU update might take like 5 to 10 minutes as well, this is not much more if that estimated time in the Xentry screen is accurate?