For 1990-2009 cars
Coolant Temp: The scan tool displays 40°C (40°F) to 140°C (284°F). This parameter is the state of the engine coolant temperature detected by the instrument panel cluster (IPC).
Coolant Temp Sensor: The scan tool displays 0-10 volts. This parameter is the state of the voltage at the coolant temp sensor detected by the IPC.
Coolant Warning Lamp: The scan tool displays On/Off. This parameter is the state of the coolant warning lamp.
ECT: The scan tool displays -40°C to 140°C (-40°F to 284°F). The Engine Coolant Temperature (ECT) sensor is mounted in the coolant stream. The engine control module (ECM) applies 5 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the ECM monitors a high signal voltage and interprets it as a cold engine. As the sensor warms (internal resistance decreases), the voltage signal decreases and the ECM interprets the lower voltage as a warm engine.