Iat Sensor.
Engine Coolant Temperature Sensor.

Fits C70, S60, S70, S80, V70, V70 XC, XC90

Engine Coolant Temperature Sensor
If your engine coolant temperature sensor has failed, you may notice one of several symptoms: your temperature gauge doesn’t move, your engine overheats without warning, your radiator fans don’t switch on, or they don’t switch off. If your Volvo has any of these symptoms, it's a good idea to let a trained Volvo technician perform an inspection.