Engine Coolant Temperature Sensor: Description
The engine coolant temperature (ECT) sensor threads into the thermostat housing just below the coolant outlet connector. See Fig 1. New sensors have sealant applied to the threads.
The ECT Sensor is a Negative Thermal Coefficient (NTC) Sensor. The resistance of the ECT Sensor changes as coolant temperature changes. This results in different input voltage to the PCM. The PCM also uses the ECT Sensor input to operate the radiator cooling fan(s), and send a message over the PCI bus to the instrument cluster for temperature gauge operation.