The engine coolant temperature sensor communicates the coolant temperature to the ECM to ensure proper air/fuel ratio, cooling fan and temperature gauge operation. Thermistor placement within the housing matches the original equipment sensor design to ensure proper output. Proper thermal conductive grease provides accurate temperature transfer to the thermistor. Causes for replacement of this sensor include check engine lights, no or erratic gauge operation, no erratic cooling fan operation, engine overheating, rough idle, engine hesitation, poor fuel economy and failed emissions tests.