It is important to conduct extensive testing during the diagnosis of an Engine Coolant Temperature (ECT) sensor. The ECT sensor, like the IAT sensor, keeps track of coolant temperature and changes resistance as it fluctuates. Trouble codes can be set off by circuit faults in the ECT sensor; moreover, this may occur due to a defect in the sensor itself or in wiring and connections. On certain engines, there are two coolant temperature sensor units; one for the instrument panel temperature gauge and another for the Electronic Engine Control (EEC) system. By disconnecting the ECT sensor and using an ohmmeter, one can see different resistance values. Make sure the right resistance is there and check the reference voltage also. To replace this part of your car's engine, cool down the motor first; then put Teflon tape on the threads of the new part before unscrewing the electrical connector plug from the old ECT sensor, attach the new one quickly and firmly bolt into place again securing tightly. Finally, reconnect the electrical connector and check the coolant levels.