DTC P0118 Engine Coolant Temperature Sensor 1 Circuit High: Notes

WARNING: This page is about a different variant/trim than selected.

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 Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Clear Memory Mode . and Inspection Mode Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Inspection Mode .
Use the check board when measuring the ECM terminal voltage and resistance.

Wiring diagram:

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

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

Courtesy of SUBARU OF AMERICA, INC.

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.] -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.
  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 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.
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 of harness between ECM connector and engine coolant temperature sensor connector.
Connector & terminal

(B135) No. 43 - (E8) No. 2:

(B135) No. 34 - (E8) No. 1:

Is the resistance less than 1 Ω?
- Yes: Go to 4.
- No: repair the harness and connector.
  NOTE:
  In this case, repair the following item:
  - Open circuit in harness between ECM connector and engine coolant temperature sensor connector
  - Poor contact of coupling connector
CHECK HARNESS BETWEEN ECM AND ENGINE COOLANT TEMPERATURE SENSOR CONNECTOR.
1. Connect all connectors.
2. Turn the ignition switch to ON.
3. Measure the voltage between ECM connector and chassis ground.
Connector & terminal

(B135) No. 43 (+) - 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 .