Circuit Description

Engine Coolant Temperature (ECT) sensor is a thermistor (resistance changes as engine coolant temperature changes). ECM supplies a 5-volt reference voltage to ECT sensor. As temperature changes, ECT sensor resistance changes, which changes voltage.

As coolant temperature decreases, ECT sensor resistance increases. As coolant temperature increases, ECT sensor resistance decreases. ECM monitors voltage input from ECT sensor and converts it into a temperature value. DTC will set when temperature does not reach 99°F (37°C) within a specified time (varies with engine starting temperature). ECT signal is continuously checked when ignition is on.