It is a common problem. The outside temp sensor is located on the downside in the right wing mirror. To fix the problem you need to unmount the mirror, unplug the round electrical wing mirror connector (with a lot of pins) and clean it by electrical contact cleaner spray. The connector comes from the door and is plugged in the mirror. Because of the conector poor design sometimes it gets wet.
Unmounting the wing mirror is not very easy task when you do it for the first time. Later it is easy. The trickiest part is unmounting the plastic mirror covers (hazard of breaking them) in order to access the 2 bolts that hold the mirror to the door. I think you need to have a look at the technical documentation.
The connector (yellow) and the temp sensor top (left down)
Sorry about my poor English.