Engine Coolant Temperature (ECT) Sensor

ECM uses ECT sensor to monitor engine coolant temperature. ECT is a thermistor (variable resistor) wired in series with a fixed resistor inside ECM. A 5-volt reference voltage is supplied and monitored by ECM. Sensor resistance, which changes according to coolant temperature, is converted to a temperature reading by ECM. High coolant temperature causes low resistance and low coolant temperature causes high resistance. The ECM uses this information for fuel control, timing, air management, idle speed and closed loop fuel control.