1.CHECK CURRENT DATA.
2) Read the data of engine coolant temperature sensor signal using Subaru Select Monitor or general scan tool.
NOTE:
• Subaru Select Monitor
For detailed operation procedure, refer to “READ CURRENT DATA FOR ENGINE”. 
• General scan tool
For detailed operation procedure, refer to the general scan tool operation manual.
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Is the temperature less than −40°C (−40°F)?
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Repair the poor contact.
NOTE:
In this case, repair the following item:
• Poor contact of engine coolant temperature sensor
• Poor contact in ECM
• Poor contact of coupling connector
• Poor contact of joint connector
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2.CHECK HARNESS BETWEEN ENGINE COOLANT TEMPERATURE SENSOR AND ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from the engine coolant temperature sensor.
3) Measure the voltage between engine coolant temperature sensor connector and engine ground.
Connector & terminal
(E8) No. 2 (+) — Engine ground (−):
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Is the voltage 10 V or more?
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Repair the short to power supply in harness between ECM and engine coolant temperature sensor connector.
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3.CHECK HARNESS BETWEEN ENGINE COOLANT TEMPERATURE SENSOR AND ECM CONNECTOR.
1) Turn the ignition switch to ON.
2) Measure the voltage between engine coolant temperature sensor connector and engine ground.
Connector & terminal
(E8) No. 2 (+) — Engine ground (−):
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Is the voltage 10 V or more?
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Repair the short to power supply in harness between ECM and engine coolant temperature sensor connector.
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4.CHECK HARNESS BETWEEN ENGINE COOLANT TEMPERATURE SENSOR AND ECM CONNECTOR.
Measure the voltage between engine coolant temperature sensor connector and engine ground.
Connector & terminal
(E8) No. 2 (+) — Engine ground (−):
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Is the voltage 4 V or more?
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Repair the harness and connector.
NOTE:
In this case, repair the following item:
• Open circuit of harness between ECM and engine coolant temperature sensor connector
• Poor contact of engine coolant temperature sensor connector
• Poor contact in ECM connector
• Poor contact of coupling connector
• Poor contact of joint connector
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5.CHECK HARNESS BETWEEN ENGINE COOLANT TEMPERATURE SENSOR AND ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Measure the resistance of harness between engine coolant temperature sensor connector and engine ground.
Connector & terminal
(E8) No. 1 — Engine ground:
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Is the resistance less than 5 Ω?
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Replace the engine coolant temperature sensor.
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Repair the harness and connector.
NOTE:
In this case, repair the following item:
• Open circuit of harness between ECM and engine coolant temperature sensor connector
• Poor contact of engine coolant temperature sensor connector
• Poor contact in ECM connector
• Poor contact of coupling connector
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