Mitusbushi XLS 2009 temperature sensor- misread outside

Most likely either the sensor has failed, or one of the connections has broken, resulting in it failing to complete the circuit, and the car is interpreting the open circuit as being the lowest temperature it can report - a friend of mine had this on an old BMW when the sensor fell off - in his case the plastic clip holding the sensor under the car had snapped.

You should be able to locate the sensor and check the resistance across it with a multimeter - if it shows infinite, then it's likely the sensor has failed. If it gives a sensible looking number, it's more likely to be one of the wires.