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

The Tech 1 displays engine coolant temperature in degrees. After engine start-up, the temperature should rise steadily to about 90°C (194°F) then stabilize when thermostat opens. If the engine has not been run for several hours (overnight), the coolant temperature and Intake Air Temperature (IAT) displays should be close to each other. A fault in the engine coolant temperature sensor circuit should set DTC P0117 or DTC P0118. These DTC charts also contain a table to check for sensor resistance values relative to temperature. Testing and Inspection