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 Mode Ref. to OPERATION , Clear Memory Mode and Inspection Mode Ref. to PROCEDURE , Inspection Mode.

Wiring diagram:

Engine Electrical System Ref. to WIRING DIAGRAM , Engine Electrical System.

Fig 1: Engine Coolant Temperature Sensor Wiring Diagram

Courtesy of SUBARU OF AMERICA, INC.

Step	Check	Yes	No
1 CHECK CURRENT DATA. Start the engine. 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". Ref. to SUBARU SELECT MONITOR General scan tool For detailed operation procedures, refer to the general scan tool operation manual.	Is the value of «Coolant Temp.» less than -40°C (-40°F)?	Go to step 2	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 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?	Repair the poor contact of ECM or engine coolant temperature sensor connector.	Go to step 3
3 CHECK HARNESS BETWEEN ECM AND ENGINE COOLANT TEMPERATURE SENSOR CONNECTOR. Turn the ignition switch to OFF. Disconnect the connector from ECM. Disconnect the connectors from the engine coolant temperature sensor. Measure the resistance of harness between ECM connector and engine coolant temperature sensor connector. Connector & terminal (E158) No. 34 - (E8) No. 1: (E158) No. 43 - (E8) No. 2:	Is the resistance less than 1 Ω?	Go to step 4	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 CONNECTOR. Connect all connectors. Turn the ignition switch to ON. Measure the voltage between ECM connector and chassis ground. Connector & terminal (E158) No. 43 (+) - Chassis ground (-):	Is the voltage 5 V or more?	Repair the short circuit of harness to power supply between ECM connector and engine coolant temperature sensor connector.	Replace the engine coolant temperature sensor. Ref. to ENGINE COOLANT TEMPERATURE SENSOR .