outside temperature indicator

Hello everyone,
I have a bit of a problem with my seat ibiza (1.4 on a y plate).

The problem is that the external temp display on the dash is reading very high (starting at about 24c and rapidly rising to the 50 c mark).
I know this is wrong because we are in freezing conditions at the moment!!!!!

Please can someone advise me on what this problem could be,
Thanks in advance,
TIM.........

i have an '02 Ibiza, mine did the same, it was the probe, and it was under warranty, but i think it's in the passenger mirror somewhere.

Hi your dead right the sensor is the little black bobble that sticks out of the bottom of the passenger door mirror easy to fix unplug old one iplug in new one and your aircon will be as good as new.The conection to plug it in is in the passenger door so you will need to take all of the internal trim off to get at it. thats the bit that takes the time. approx 2 hours tops to do the job carefully ie (no broken trim)