We have our A6 2.0tdi for just over a week now, on the test drive, stop start fault. Function unavailable appeared on the dash. Told the salesman about it and he assured us it was just because the battery was low, with it sitting on the forecourt.
Anyway, it has been randomly coming up with it every so often, jst the message in the dash, no other warnings. Been back to the seller and they still insist it's just because it's not ready, heater on, battery low all that stuff, but I thought if that was the case you get the A with a circle round it and line through it. They have scanned it and no errors were present.

They have booked us in to have the car checked again in a couple of weeks time. It seems from the searching I have done, it's quite common, to get the message but not so easy to find out what's causing.

Anyone else had this?.