DTC P0118: Engine Coolant Temperature Sensor 1 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 (CROSSTREK MODEL)>Engine Electrical System>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

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

      Data Monitor 

      NOTE:

      • SUBARU SELECT MONITOR

        For detailed operation procedures, refer to "Data Monitor". Ref. to ENGINE (DIAGNOSTICS) (H4DO)>DATA MONITOR .

      • General scan tool

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

   Is the value of [Coolant Temp.] -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 of ECM and engine coolant temperature sensor connector.

   Is there poor contact of ECM or engine coolant temperature sensor connector?

   Yes:  Repair the poor contact of ECM or engine coolant temperature sensor connector.

   No:  Go to  3.

3. CHECK HARNESS BETWEEN ECM AND ENGINE COOLANT TEMPERATURE SENSOR (OPEN)  .
   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 of harness between ECM connector and engine coolant temperature sensor connector.

      Connector & terminal 

      (E158) No. 45 - (E8) No. 2:

      (E158) No. 54 - (E8) No. 1:

   Is the resistance less than 1 Ω?

   Yes:  Go to  4.

   No:  Repair the open circuit of the harness between the ECM connector and engine coolant temperature sensor connector.

4. CHECK HARNESS BETWEEN ECM AND ENGINE COOLANT TEMPERATURE SENSOR (SHORT TO POWER SUPPLY)  .
   1. Connect all connectors.
   2. Turn the ignition switch to ON.
   3. Measure the voltage between ECM connector and chassis ground.

      Connector & terminal 

      (E158) No. 45 (+) - Chassis ground (-):

   Is the voltage 5 V or more?

   Yes:  Repair the short circuit of harness to power supply between ECM connector and engine coolant temperature sensor connector.

   No:  Replace the engine coolant temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>ENGINE COOLANT TEMPERATURE SENSOR .