Albourneboy

The reading from the outside air temperature sensor is used by the C5's air con system to help regulate the air temperature inside the car. When the sensor fails, it would appear that it goes into some sort of grossly over-reading mode (mine is currently showing anywhere between 46 and 72 degrees C!!! in the UK!!! in December!!!!). Hopefully, replacing the sensor will sort things out but as yet, I am unable to get the car in the dealers - they are too busy. I spoke to the dealer yesterday and they said that all they would do is pop off the wing mirror cover, replace the sensor, pop on the cover and job done. The sensor can be seen poking out of a hole in the bottom of the left hand door mirror but as for 'popping off' the cover, I have had a look and can't see how this can be done. If anyone has any ideas, let me know - it could save me £30 in labour charges. Back to your problem - get the sensor replaced but in the meantime, switch off the air-con and don't use auto mode. You will probably still have to turn the temp settings up high but at least you should get some heat from the system