Exterior temp sensor acting crazy.

It's on a 56 1.4l Turbo Diesel. For the most part the sensor doesn't read anything but in certain circumstances it gives off some very strange readings. For example it was quite cold the other day and the sensor was reading -35c?

Could it be a dodgy contact if so where in the engine bay is the sensor and anyone know how easy it is to get at or is it more likely that the sensor has just failed and needs to be replaced?