Engine Coolant Temperature Sensor
On the 2.0L, the Engine Coolant Temperature (ECT) sensor threads into the rear of the cylinder head, next to the camshaft position sensor. See Fig 1. On the 2.4L, the ECT sensor threads into the thermostat housing just below the coolant outlet connector. See Fig 2.
On all models, 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 voltages to the Powertrain Control Module (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.
The ECT sensor provides an input to the PCM. As temperature increases, resistance of the sensor decreases. As coolant temperature varies, the ECT sensor resistance changes resulting in a different voltage value at the PCM ECT sensor signal circuit. The ECT sensor provides input for various PCM operations. The PCM uses the input to control air/fuel mixture, timing, and radiator fan on/off times. The PCM uses ECT sensor input to send messages over the PCI bus for temperature gauge operation.