Hi,
I know this is an older post, but I've literally just been informed of this software update.
Basically, several weeks ago now, I got the Airbag recall letter for my 2012 C350cdi Sport. I called the local MB Dealer (not the one I used to use, I'm not down that way any more) and was told there was some additional software update I was due as well, but they did not have the details of it to hand. As my car is booked in for tomorrow, I just got the online Check In email sent to me, so I checked in, as it said it will have the complete schedule of work.
Now, I'd previously said to the dealer that under no circumstances did I want an anonymous update performed on my car, where they cannot tell me what it does. Period. They mentioned it would be discussed when I got there. However, the schedule of works I got when checking in clearly shows it's software update SMPC756 they're talking about. So, now I know what they're planning and will clearly refuse the update.
However, I do wonder where I stand if MB ignore my request? If they wreck my fuel economy / performance I'll be very unhappy. My car is running very well indeed, will happily get 50+ mpg on a long run, flies through the MoT with the testers remarking how clean it runs. The car doesn't get used much, perhaps once or twice a week, but does do a reasonable distance when it is used. I really don't want to rock the boat when it's running, and has been running well for the past almost ten years of ownership.