DTC P0117: Engine Coolant Temperature Sensor 1 Circuit Low: Notes

DTC detecting condition: 

Immediately at fault recognition

Trouble symptom: 

• Hard to start
• Improper idling
• Poor driving performance

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 «Coolant Temp.» 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 instructions.

   Is the value of «Coolant Temp.» 150°C (302°F) or more?

   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 HARNESS BETWEEN ECM AND ENGINE COOLANT TEMPERATURE SENSOR CONNECTOR. 
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from ECM.
   3. Disconnect the connectors from the engine coolant temperature sensor.
   4. Measure the resistance between the ECM connector and engine ground.

   Connector & terminal 

   (E158) No. 38 - Engine ground:

   Is the resistance 1 MΩ or more?

   Yes:  Replace the engine coolant temperature sensor. Refer to FUEL INJECTION (FUEL SYSTEMS) (EXCEPT FOR STI)>ENGINE COOLANT TEMPERATURE SENSOR .

   No:  Repair the short circuit to ground in harness between ECM connector and engine coolant temperature sensor connector.