hello carfree....a similar question I made in another post for a smart four four with manual transmission, with regard to the battery.
I imagine that you'll not do this work without disconnecting the battery.
in the case of the automatic transmission, I don't know sequentially, after removing the current and required a realignment of the exchange.
I found this procedure on the network
http://www.notiziariomotoristico****...she-smart-451
see if you can be useful.
you hear of others who perhaps are more experienced.