Hi There,

Thank you for reading this post.

Recently I brought my 2017 C43 coupe for a 40K B service at a MB dealer. After I got my car back, I noticed that the transmission behaves differently. In Sport+ mode, it becomes more jerky. In Eco mode, it would glide a shorter period than before and would exit the glide mode with a more noticeable jerk. Also the gear shift becomes more unpredictable. The gear box was not the smoothest at the beginning but it understood my intention pretty well in all modes. Now everything changed, especially in Sport and Sport+ mode. At cruising speed, sometimes a tiny bit of gas would make the gear box downshift but other times, even at the same speed and same gear, more throttle wouldn't make it downshift. It's like you and your old friend don't recognize each other suddenly, which is so frustrating.

There are some changes to the exhaust note. For example, previously when I'm in Sport+ mode at 3rd or 4th gear, if the rpm is about 3k and I lift the throttle, the car will make some burble. It was pretty predictable. After the maintenance it wouldn't do that or only make some very short burble. The change in the exhaust note pattern is pretty noticeable. I'm a little bit frustrated after the maintenance and will schedule a revisit to the dealer.

The only change I like is, when start up the car in Sport+ mode, the engine will rev to 2K+ rpm and give some crackle and pops, which it didn't do before. I've attached a video showing the start up.

With all these changes, I'm a little bit worried that some might be something wrong during the maintenance. Do you have any idea what might have been done to the car in the maintenance to cause these changes? I would really appreciate your input! Thanks.

 

If a transmission/ECU update was applied, think of your car being reset to the point when it drove off the lot for the first time.There's a certain amount "learning" it does to fine tune itself to your driving style. Keep driving and it *should* adapt back to your style a bit. Now, the S+ start up burble is interesting...

 

It depends on what the dealership did. If they had to disconnect the battery then your transmission (TCU) could have been reset. After you drive it for a bit, it should learn your driving habits and smooth out.

 

Hi Richard, Ramsino, thank you for the information. From you experience, how long will it take for this "re-adapt" period? I've been driving the car for more than 1k miles after the maintenance but it is still quite different from what it was. Also about the rev-up and burble when start in Sport+, will the TCU reset cause it as well?

 

If the dealer performed transmission reset, it will take 40 different shift points to complete the learning cycle.

As for the s+ startup, my car does same burbles but haven't given any attention on the rpm it goes up to.

I would reset the transmission again and drive like granny on comfort for few hours. Unless you want your car to shift at higher rpm, pop it on s+ from reset.

 

1k miles should have been more than enough. Maybe you should perform a TCU reset yourself as others have suggested. There is a post somewhere on these forums regarding the resetting process. You can also just google it as well.

 

Just checked with the dealer today, according to them there was no software update down to the the car. Just oil change, filter change, tire pressure check, etc... It's really hard to get a direct answer from them. I tried to ask what could cause this behavior change. They just kept repeating this seems normal, didn't gave any clue on why it is different.

 

Do you have the paperwork from the previous service? They are suppose to record everything on there.

 

Yes, I do have the paperwork. Here it goes. I've covered some personal information and the dealer information.


There are some mistakes on it. First my car is a coupe, should be C43C4 not C43A4. The tire pressure is wrong as well. They were inflated to 44 in the front, 38 in the rear. Have to manually deflate the tire a little bit. According to the paper, they adjust the tire pressure based on the specs of r18 wheels while mines are r19 . These mistakes also made me not very confident in the dealer that they actually did right to the transmission.