Coolant Temperature Sensor/Switch (For Computer): Description and Operation

Voltage Versus Temperature Chart:

The ECT sensor is a thermistor (a resistor that changes value due to temperature) mounted in the engine coolant flow. High coolant temperatures result in low resistance and low temperatures result in high resistance. The PCM provides a 5 volt reference signal and a ground to the ECT sensor, and it measures the voltage signal as it changes due to the sensors resistance. A high coolant temperature will result in low signal voltage (near 0 volt) and low coolant temperature will result in high signal voltage (near 5 volts).

The ECT sensor circuit uses two different temperature sensing circuits for two temperature ranges - below 50°C (122°F) and above 50°C (122°F). The PCM will shift between a high resistance circuit for low temperatures and a low resistance circuit for high temperatures.