Cruise control downshift.
 

Hi there. I have a 200 C220cdi with tiptronic box. Recently,when driving on motorways, it has started changing down after I have accelerated with the cruise control on.Any ideas would be much appreciated.

Is this not normal?
My 210 downshifts when using the cruise control to accelerate and the shifts up when the set speed is reached. Uphills also cause downshifts sometimes...

cruise control downshift
 

Yes, changing down is normal under certain circumstances. It will happen if you are descending a steep hill and require extra engine breaking or accelerating hard. What is happening is something different. If I am cruising at a (hypothetical) speed of 75mph and accelerate when I lift off the speed drops normally but then the 'box changes down. I end up cruising at the set speed in fourth gear at which point I flick it up into fifth. I have had the car for four years and have covered a fair few long distance motorway miles in it whilst going on holiday and it has only just started doing this. I see that there are two control units for the CC. One electronic and the other which looks mechanical/electrical. I was wondering if one of these was faulty and if so which I should suspect first.