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

1. -

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 .

Courtesy of SUBARU OF AMERICA, INC.

CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>GENERAL DESCRIPTION>PREPARATION TOOL>HOW TO USE CHECK BOARD .

NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

CHECK DATA MONITOR .
1. Start the engine.
2. Using the Subaru Select Monitor, read the value in [Engine Oil Temperature].
  NOTE: For detailed operation procedures, refer to "Common (Diagnostics)". Ref. to COMMON (DIAG)>DATA MONITOR .
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 again.

NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.
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 .
CHECK HARNESS BETWEEN ECM AND ENGINE OIL TEMPERATURE SENSOR CONNECTOR (OPEN) .
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 and terminal
  
  (E158) No. 46 - (E75) No. 2:
  
  (E158) No. 58 - (E75) No. 1:
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.
CHECK HARNESS BETWEEN ECM AND ENGINE OIL TEMPERATURE SENSOR CONNECTOR (SHORT TO POWER SUPPLY) .
1. Connect all connectors.
2. Turn the ignition switch to ON.
3. Measure the voltage between ECM connector and engine ground.
  Connector and terminal
  
  (E158) No. 46 (+) - 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. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>ENGINE OIL TEMPERATURE SENSOR .