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

Fig 1: Engine Coolant Temperature Sensor 1 Circuit Low - Wiring Diagram

Courtesy of SUBARU OF AMERICA, INC.

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

   • Subaru Select Monitor

     For detailed procedures, refer to "Data Monitor". Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Subaru Select Monitor .

   • General scan tool

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

   Is the value of [Coolant Temp.] 120°C (248°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.
     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 connectors from the engine coolant temperature sensor.
   3. Disconnect the connector from ECM.
   4. Measure the resistance between ECM connector and chassis ground.

   Connector & terminal 

   (B135) No. 43 - Chassis ground:

   Is the resistance 1 MΩ or more?

   • Yes: Replace the engine coolant temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Engine Coolant Temperature Sensor .
   • No: Repair the short circuit to ground in harness between ECM connector and engine coolant temperature sensor connector.