Engine Coolant Temperature (ECT) Sensor

The Engine Coolant Temperature (ECT) sensor (thermistor) is installed at rear of intake manifold, near left rocker arm cover. See Figure. The coolant temperature sensor resistance is high at low temperatures and decreases as temperature rises. The ECA applies a 9-volt reference voltage to sensor and monitors the resultant voltage drop across sensor.

If coolant temperature is less than 70°F or greater than 230°F, the ECA will cut off all EGR flow. Also, if engine coolant overheats from prolonged idle, the ECA will advance initial engine timing to increase engine speed and improve cooling.