1.CHECK FOR ANY OTHER DTC ON DISPLAY.
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Is any other DTC displayed?
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Check DTC using “List of Diagnostic Trouble Code (DTC)”. 
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2.CHECK FRONT OXYGEN (A/F) SENSOR DATA.
2) While observing the Subaru Select Monitor or general scan tool screen, warm up the engine until engine coolant temperature is above 75°C (167°F).
When the engine is already warmed up, keep the engine idling for one minute or more.
3) Read the data of front oxygen (A/F) 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 procedures, refer to the general scan tool operation manual.
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Is the voltage 2 — 2.3 V?
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3.CHECK FRONT OXYGEN (A/F) SENSOR DATA.
Race the engine at speeds from idling to 3,000 rpm for a total of 5 cycles.
NOTE:
• Normally, the air fuel ratio is rich at racing.
• To increase engine speed to 3,000 rpm, slowly depress accelerator pedal for approximately 5 seconds, and quickly release accelerator pedal to decrease engine speed.
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Is the voltage less than 2.15 V?
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4.CHECK HARNESS BETWEEN ECM AND FRONT OXYGEN (A/F) SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM and front oxygen (A/F) sensor connector.
3) Measure the resistance between ECM and front oxygen (A/F) sensor connector.
Connector & terminal
Euro 4 model
(B134) No. 18 — (E23) No. 3:
(B134) No. 28 — (E23) No. 1:
Euro 5 model
(B137) No. 14 — (E23) No. 1:
(B137) No. 23 — (E23) No. 3:
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Is the resistance less than 1 Ω?
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Repair the harness and connector.
NOTE:
In this case, repair the following item:
• Open circuit in harness between ECM and front oxygen (A/F) sensor connector
• Poor contact of coupling connector
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5.CHECK HARNESS BETWEEN ECM AND FRONT OXYGEN (A/F) SENSOR CONNECTOR.
Measure the resistance between ECM and chassis ground.
Connector & terminal
Euro 4 model
(B134) No. 18 — Chassis ground:
(B134) No. 28 — Chassis ground:
Euro 5 model
(B137) No. 14 — Chassis ground:
(B137) No. 23 — Chassis ground:
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Is the resistance 1 MΩ or more?
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Repair the ground short circuit of harness between ECM and front oxygen (A/F) sensor connector.
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6.CHECK EXHAUST SYSTEM.
Check exhaust system parts.
NOTE:
Check the following items.
• Looseness and improper fitting of exhaust system parts
• Damage (crack, hole etc.) of parts
• Looseness of front oxygen (A/F) sensor
• Loose part and improper installation between front oxygen (A/F) sensor and rear oxygen sensor
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Is there any fault in exhaust system?
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Repair or replace faulty parts.
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Replace the front oxygen (A/F) sensor.
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