If that doesn't help then it could be a fault with the connector between the engine bay wiring loom and the bumper wiring loom. It is located inside the engine bay on the left hand side, quite a long way down, attached to the member that goes from the front of the car to the back. Sorry - it's difficult to describe exactly where it is, but if you grab a torch and trace the wiring you can probably find it. If you've ever taken the bumper off, yoiu'll know exactly where it is!
EDIT: actually it's on this video, at 5:06.
https://www.youtube.com/watch?v=7BUGH4_VMkU
It houses the connection for the outside temperature sensor so if your dash also reads 30 degrees C then it's very likely to be this multi-plug.