The transmission control in my new '06 C55 seems at odds with the book, but the Saturday on-call service advisor says it's working as designed. I'm not ready to believe him yet.

I expected a single pull of the shift lever to D- (or tap on the - paddle) to consistently drop one gear. This is what my '01 S55 does and what the C55 manual documents. But it drops several gears, as it thinks appropriate. At idle it locks into 1, at 20MPH to 2, etc. It looks like it's acting as if I've held the shift lever for a few seconds, but it's what happens on a quick pull. This is in C or S modes.

Is this mind-of-its own behavior something normal, or should I be able to downshift n gears with n taps like I'm used to? Thanks in advance.

Martin

 

yes. you can downshift anytime.

but upshift, it's slightly different. if it exceeds the threshold, it will shift up in order to avoid damage on over revving.

 

Thanks for the response, but I'm not sure that you're answering my question.

When I downshift, should I be able to always downshift exactly one gear with one tap, or do I have to let the transmission controller decide what gear to downshift me into?

Martin

 

yes, it will downshift to the gear of your intention (as shown in the cluster).

there can be a split seconds delay, but it will downshift.

 

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Thanks again. Yes, that is how I interpreted the manual. I guess I'll have to go back Monday when someone a bit more knowlegeable about the transmission is there. Hopefully they will just have to reflash the controller.

Martin

 

Well, I'm afraid the book is wrong. The tranny guy at the dealer confirmed that these have "one touch" download programs. Even a short pull or tap on the steering wheel button directs the TCM to select the "appropriate" gear. No single-gear downshift behavior in C or S.

I'm still not crazy about having to glance at the cluster to know what gear I've been put in, but I'm told the automatic selection works pretty well.

Martin

 

My C55 trans shifts one gear for every tap, it has never shifted more than the number of gears I request of it. My C55 is an '05 so maybe the way yours works is different for '06.

 

Yes. The "smarter" program is new. I'm not sure if it was introduced at the '06 model year start, earlier or later. But the '06 C55-only manual doesn't document it although the dealer confirms it was an intentional change and improvement.

Martin