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
Wiring diagram:

Engine Electrical System Ref. to WIRING SYSTEM (IMPREZA MODEL)>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM . Ref. to WIRING SYSTEM (CROSSTREK MODEL (EXCEPT FOR HEV))>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .
- IMPREZA MODEL
Courtesy of SUBARU OF AMERICA, INC.
- CROSSTREK MODEL
Courtesy of SUBARU OF AMERICA, INC.

CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Ref. to ENGINE (DIAGNOSTICS) (H4DO 2.0 (EXCEPT FOR HEV))>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 2.0 (EXCEPT FOR HEV))>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

CHECK DATA MONITOR .
1. Start the engine.
2. Using the Subaru Select Monitor or a general scan tool, read the value of [Engine Coolant Temperature].
  NOTE:
  - Subaru Select Monitor For detailed operation procedures, refer to "Common (Diagnostics)". Ref. to COMMON (DIAG)>DATA MONITOR .
  - General scan tool For detailed operation procedures, refer to the general scan tool operation manual.
  Is the value of [Engine Coolant 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 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 (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 and terminal
  
  (E158) No. 59 - (E8) No. 2:
  
  (E158) No. 58 - (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 J/C
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 and terminal
  
  (E158) No. 59 (+) - 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 (EXCEPT FOR HEV))>ENGINE COOLANT TEMPERATURE SENSOR .