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
  CAUTION:

  • After servicing or replacing faulty parts, perform Clear Memory Mode Refer to ENGINE (DIAGNOSTICS) (EXCEPT FOR STI)>CLEAR MEMORY MODE>OPERATION , and inspection mode Refer to ENGINE (DIAGNOSTICS) (EXCEPT FOR STI)>INSPECTION MODE>PROCEDURE ..
  • Use the check board when measuring the ECM terminal voltage and resistance.

Wiring diagram: 

Engine Electrical System Refer to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK CURRENT DATA. 
   1. Start the engine.
   2. Read the value of «Oil Temperature» using the Subaru Select Monitor or a general scan tool.
      NOTE:

      • Subaru Select Monitor

        For detailed operation procedures, refer to "Current Data Display For Engine". Refer to ENGINE (DIAGNOSTICS) (EXCEPT FOR STI)>SUBARU SELECT MONITOR .

      • General scan tool

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

   Is the value of «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 again.

   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 connector from ECM.
   3. Disconnect the connectors from the engine oil temperature sensor.
   4. Measure the resistance of the harness between the ECM connector 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 ECM connector 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 connector 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 connector and engine oil temperature sensor connector.

   No:  Replace the engine oil temperature sensor. Refer to FUEL INJECTION (FUEL SYSTEMS) (EXCEPT FOR STI)>ENGINE OIL TEMPERATURE SENSOR .