1.CHECK EXHAUST SYSTEM.
Check for gas leaks or air suction caused by loose or dislocated nuts and bolts, and open hole at exhaust pipes.
NOTE:
Check the following positions.
• Between cylinder head and front exhaust pipe
• Between front exhaust pipe and front catalytic converter
• Between front catalytic converter and rear catalytic converter
• Loose or improperly attached front oxygen (A/F) sensor or rear oxygen sensor
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Is there any fault in exhaust system?
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Repair or replace the exhaust system. 
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2.CHECK WAVEFORM DATA ON THE SUBARU SELECT MONITOR (WHILE DRIVING).
1) Drive at a constant speed between 80 — 112 km/h (50 — 70 MPH).
2) After 5 minutes have elapsed in the condition of step 1), use the Subaru Select Monitor while still driving to read the waveform data.
• At normal condition
• At abnormal condition (numerous inversion)
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Is a normal waveform displayed?
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Even if DTC is detected, the circuit has returned to a normal condition at this time. Reproduce the fault condition, and reperform the check.
NOTE:
In this case, there may be a temporary connector contact failure.
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3.CHECK WAVEFORM DATA ON THE SUBARU SELECT MONITOR (WHILE IDLING).
1) Run the engine at idle.
2) In the condition of step 1), use the Subaru Select Monitor to read the waveform data.
• At normal condition
• At abnormal condition 1 (numerous inversion)
• At abnormal condition 2 (noise input)
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Is a normal waveform displayed?
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• The waveform is displayed at abnormal condition 1:
• The waveform is displayed at abnormal condition 2:
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4.CHECK CATALYTIC CONVERTER.
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Is the catalytic converter damaged?
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Replace the catalytic converter.
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5.CHECK REAR OXYGEN SENSOR CONNECTOR AND COUPLING CONNECTOR.
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Has water entered the connector?
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Completely remove any water inside.
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6.CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and rear oxygen sensor.
3) Measure the resistance of harness between ECM and rear oxygen sensor connector.
Connector & terminal
(B135) No. 4 — (E22) No. 3:
(B134) No. 29 — (E22) No. 4:
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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 rear oxygen sensor connector
• Poor contact of coupling connector
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7.CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to ON.
2) Measure the voltage between rear oxygen sensor connector and chassis ground.
Connector & terminal
(E22) No. 3 (+) — Chassis ground (−):
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Is the voltage 0.2 — 0.5 V?
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Repair the harness and connector.
NOTE:
Repair the following locations.
• Open circuit of harness between the ECM and rear oxygen sensor
• Poor contact of the ECM and rear oxygen sensor
• Poor contact in ECM connector
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8.CHECK REAR OXYGEN SENSOR SHIELD.
1) Turn the ignition switch to OFF.
2) Expose the rear oxygen sensor connector body side harness sensor shield.
3) Measure the resistance between the sensor shield and chassis ground.
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Is the resistance less than 1 Ω?
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Replace the rear oxygen sensor.
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Repair the open circuit in the rear oxygen sensor harness.
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