The ambient temperature display measures a fixed 78-79Farenheit & never changes. I have used VAG Com and there are no error codes reported on the outside temp sensor which is positioned behind the front bumper. I also unplugged it at the 'plug end'(fairly sure it was the right plug - passenger side under and next to small filler tank - hydraulics) and the dash ambient temp reading remained the same ie 78F - even with the sensor disconnected ?! Yes, it is a UK car, so not sure why its not in C.
Should also add the dash has a faulty water temp gauge which is a cluster issue..
2000 c5 A6 Avant 2.4