Question about temperature of car

This is usually because the outside temperature is close to freezing - leading to the risk of black ice.

Unless this is listed as a fault condition where the car is not getting that particular reading.

I concur with mike's answer hat it's a warning of low external temperatures making road icing more likely, and wish to add that in these cases you may also see an indicator like a snowflake in the display. The temperature the indicator appears at varies between manufacturers but most cars warn of low temperature when then external temperature is between 2 and 4 degrees C