1.CHECK CURRENT DATA.
2) Read the data of intake air temperature sensor signal using Subaru Select Monitor or general scan tool.
NOTE:
• Subaru Select Monitor
For detailed operation procedures, 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 intake air temperature less than −40°C (−40°F) ?
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Even if the malfunction indicator light illuminates, 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 may be the cause.
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2.CHECK POOR CONTACT.
Check for poor contact in ECM or the mass air flow and intake air temperature sensor connector.
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Is there poor contact in ECM or the mass air flow and intake air temperature sensor connector?
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Repair the poor contact in ECM or the mass air flow and intake air temperature sensor connector.
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3.CHECK HARNESS BETWEEN ECM AND MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and the mass air flow and intake air temperature sensor.
3) Measure the resistance of harness between ECM and the mass air flow and intake air temperature sensor connector.
Connector & terminal
(B135) No. 18 — (B3) No. 1:
(B135) No. 30 — (B3) No. 2:
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Is the resistance less than 1 Ω?
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Repair the open circuit of harness between ECM and mass air flow and intake air temperature sensor connector.
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4.CHECK HARNESS BETWEEN ECM AND MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR CONNECTOR.
1) Connect all the connectors.
2) Turn the ignition switch to OFF.
3) Measure the voltage between ECM and chassis ground.
Connector & terminal
(B135) No. 18 (+) — Chassis ground (−):
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Is the voltage 5 V or more?
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Repair the short circuit of harness to power supply between ECM and the mass air flow and intake air temperature sensor connector.
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Replace the mass air flow and intake air temperature sensor.
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