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

The Engine Coolant Temperature (ECT) sensor is a thermistor which changes resistance to reflect changes in temperature. When the ambient temperature is low, the resistance of the ECT is high. When the ambient temperature is high, the resistance of the ECT is low. The ECT has a signal circuit and a ground circuit. The ECM supplies 5 V to the signal line which is pulled-up through a pull-up resistor. The signal voltage is monitored for changes in sensor resistance in order to determine engine coolant temperature.

The ECT signal is used by the ECM for fuel control, ignition timing, EGR operation, EVAP canister purge control, and closed loop fuel operation.