For some weeks now my mother-in-law's Peugeot 207 (2009 model I think) shows a wrong outside temperature. While the actual outdoor temperature has been somewhere around freezing (0°C) the temperature display showed something like -7°C to -12°C.
It is not static but floats by some degrees up and down over the time the car is in use. First I thought it's just off by some 10°C or so, but it seems to be more complicated: Even if the car was parked in an underground parking for some hours where the temperature is surely around 10°C or warmer, the sensor then displays some -7°C or so. So to me it looks like it's some combined offset and proportionality issue.
Is there something I can try out myself to narrow things down or something that I can try to fix myself (connectors that could have gone loose or stuff like that)? If yes, where would I have to search? Or is this likely to be a software issue that needs a mechanic and special equipment?