Engine Coolant Temperature (ECT) Sensor

The ECT sensor is located on intake manifold, near thermostat housing. ECT sensor consists of a temperature dependent resistive metal strip. ECT sensor output voltage changes as engine coolant temperature changes. See ECT SENSOR OUTPUT VOLTAGE  table. ECT works as a Negative Temperature Coefficient (NTC) sensor. As coolant temperature increases, sensor resistance decreases, as coolant temperature decreases, sensor resistance increases. See ECT SENSOR RESISTANCE table. ECM monitors ECT sensor resistance values and triggers enrichment circuits to extend injector on-time during cold starting and warm-up (a richer mixture at low coolant temperatures). ECM also uses ECT sensor values for Secondary Air Injection activation. See SECONDARY AIR INDUCTION  under AIR INDUCTION SYSTEM.

Default strategy for ECT sensor is to select a substitute value based on intake air temperature. Initial ECT sensor default value selected will increase to a pre-warm up value over a time period programed for each default. An ECT sensor fault may result in a fast idle condition on initial start-up until fully warm value is reached. There may be a hot engine restart problem. A fault is indicated by illumination of the MIL.