Ensure the temperature is set on Celcius and not Farenheit first off. The temp. may be showing 75F and it may be whatever that is in Celcius (30 ?) which would look like it is incorrect. If this is correct then suspect faulty ambient air temperature sensor. Ambient sensor is located behind center of front bumper, pictured below..
First inspect wiring to the sensor, if wiring is OK then replace sensor.