Temperature sensor is temperature sensitive semiconductor resistor, which usually has negative temperature coefficient (NTC), meaning that the resistance goes down with increasing temperature. The opposite type – positive (PTC) is very rare. Application:
– engine coolant temperature sensor
– air temperature sensor
– oil temperature sensor
– fuel temperature sensor

Typical location of the engine coolant temperature sensor.

Connection of the USB Autoscope IV to the sensor signal wire.

Setting the USB Autoscope IV to the temperature sensor testing mode.

Output voltage waveform of the engine coolant temperature sensor in good condition on Mitsubishi Lancer 1.6 2005, recorded while the engine was cold and running at idle.

Output voltage waveform of the engine coolant temperature sensor with a malfunction, recorded while the engine was cold and running at idle.

Output voltage waveform from a properly functioning engine coolant temperature sensor. Output voltage of an NTC sensor decreases with increasing temperature, due to the way the circuit is designed.

Output voltage waveform from a malfunctioning engine coolant temperature sensor. The sensor circuit develops an intermittent connection as the sensor heats up.

Output voltage waveform from a malfunctioning engine coolant temperature sensor. The sensor circuit develops an intermittent connection as the sensor heats up.

Output voltage waveform from a malfunctioning engine coolant temperature sensor.

Output voltage waveform from a properly functioning fuel temperature sensor of diesel engine