Engine Coolant Temperature Sensor (ECT)
The ECT sensor is a thermistor (a resistor which changes value based on temperature) mounted in engine coolant flow. At cold coolant temperatures, ECT sensor resistance is high and at hot coolant temperatures, resistance of sensor is low. The PCM supplies a 5 volt reference signal and a ground to sensor and measures voltage signal as it is changed by sensor. The voltage is close to 5 volts at cold temperatures and close to zero volts at hot temperatures.
The PCM uses ECT information for fuel enrichment, ignition control, canister purge control, idle speed control and "Closed Loop" fuel control. A faulty ECT sensor may cause various driveability conditions and should set a PCM Trouble Code.