Coolant Temperature Sensor/Switch (For Computer): Testing and Inspection

A Tech 1 scan tool displays engine coolant temperature (ECT) in degrees centigrade. After the engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens. If the engine has not been run for several hours (overnight) the engine coolant and intake air temperatures should be within 5 degrees of each other. A fault in the ECT sensor circuit should set a DTC 14 or DTC 15. The Diagnostic Trouble Code (DTC) charts also contain a "Diagnostic Aid" chart to check for sensor resistance values relative to temperature.