Technician Handbook ! 673 Electronic & Computer Controlled Systems Variable Resistance Input A temperature sensor is a type of variable resistor whose resistance changes with temperature. This type of sensor is often called a thermistor. Two types of thermistor are: Positive temperature coefficient (PTC) thermistor – resistance increases as temperature increases Negative temperature coefficient (NTC) thermistor – resistance decreases as temperature increases Thermistors are commonly used for engine coolant temperature sensors and ambient temperature sensors. Modern Toyota vehicles use NTC thermistors exclusively. Technical Training 11