DTC P0198 Engine Oil Temperature Sensor "A" Circuit High: Notes

DTC detecting condition: 

Immediately at fault recognition

Trouble symptom: 

• Hard to start
• Improper idling
• Poor driving performance

Wiring diagram: 

Engine Electrical System Ref. to WIRING SYSTEM>Engine Electrical System>WIRING DIAGRAM .

1. CHECK CURRENT DATA. 
   1. Start the engine.
   2. Using the Subaru Select Monitor or a general scan tool, read the value of [Engine Oil Temperature].
      NOTE:

      • Subaru Select Monitor

        For detailed procedures, refer to "Data Monitor". Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>Subaru Select Monitor .

      • General scan tool

        For detailed operation procedures, refer to the general scan tool operation manual.

   Is the value of [Engine Oil Temperature] -40°C (-40°F) or less?

   • Yes: Go to  2.
   • No: Even if DTC is detected, the circuit has returned to a normal condition at this time. Reproduce the failure, and then perform the diagnosis.
   NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.
2. CHECK FOR POOR CONTACT. 

   Check for poor contact between the ECM and engine oil temperature sensor connectors.

   Is there poor contact of the ECM or engine oil temperature sensor connectors?

   • Yes: Repair the poor contact of ECM or engine oil temperature sensor connector.
   • No: Go to  3.
3. CHECK HARNESS BETWEEN ECM AND ENGINE OIL TEMPERATURE SENSOR CONNECTOR. 
   1. Turn the ignition switch to OFF.
   2. Disconnect the connectors from the engine oil temperature sensor.
   3. Disconnect the connector from ECM.
   4. Measure the resistance of the harness between the ECM and engine oil temperature sensor connector.

      Connector & terminal 

      (E159) No. 27 - (E75) No. 1:

      (E158) No. 2 - (E75) No. 2:

   Is the resistance less than 1 Ω?

   • Yes: Go to  4.
   • No: Repair the open circuit in the harness between the ECM and engine oil temperature sensor connector.
4. CHECK HARNESS BETWEEN ECM AND ENGINE OIL TEMPERATURE SENSOR CONNECTOR. 
   1. Connect all connectors.
   2. Turn the ignition switch to ON.
   3. Measure the voltage between ECM and engine ground.

      Connector & terminal 

      (E158) No. 2 (+) - Engine ground (-):

   Is the voltage 5 V or more?

   • Yes: Repair the short circuit to power in harness between ECM and engine oil temperature sensor connector.
   • No: Replace the engine oil temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>Engine Oil Temperature Sensor .