1.CONNECT SUBARU SELECT MONITOR OR GENERAL SCAN TOOL, AND READ THE DATA.
1) Turn the ignition switch to OFF.
2) Connect the Subaru Select Monitor or general scan tool to data link connector.
3) Turn the ignition switch to ON, and the Subaru Select Monitor or general scan tool power switch to ON.
5) Read the mass air flow sensor voltage 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 voltage 0.2 — 4.7 V?
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Even if the malfunction indicator light illuminates, the circuit has returned to a normal condition at this time.
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2.CHECK HARNESS BETWEEN ECM AND MASS AIR FLOW SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from mass airflow sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between mass air flow sensor connector and chassis ground.
Connector & terminal
(B3) No. 3 (+) — Chassis ground (−):
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Is the voltage 5 V or more?
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Repair the short to power supply in the harness between the mass air flow sensor connector and ECM connector.
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3.CHECK HARNESS BETWEEN ECM AND MASS AIR FLOW SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from the ECM.
3) Measure the resistance of harness between ECM connector and mass air flow sensor connector.
Connector & terminal
(B3) No. 2 — (B135) No. 34:
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Is the resistance less than 1 Ω?
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Replace the mass air flow sensor.
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Repair the open circuit of harness between mass air flow sensor connector and ECM connector.
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