Engine Coolant Temperature (ECT) Sensor

The ECT sensor is a thermistor (temperature sensitive resistor) located in an engine coolant passage. The PCM supplies and monitors a 5-volt signal to ECT sensor. This monitored 5-volt signal is then reduced by resistance of the CTS. When coolant temperatures are low, ECT sensor resistance is high, and a high monitored voltage signal is seen by the PCM. When coolant temperatures are high, ECT sensor resistance is low, and a low monitored voltage is seen by the PCM. When fully warmed, ECT sensor should reflect a temperature of at least 185°F (85°C).

Coolant temperature input is used in the control of fuel delivery, ignition timing, idle speed, cooling fan operation, emission control devices and converter clutch application. An ECT sensor which is out of calibration will not set a trouble code but will cause fuel delivery and driveability problems. A coolant sensor circuit problem (open or short to ground) will swing monitored voltage high or low and should set a related trouble code.