1.CHECK FRONT OXYGEN (A/F) 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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2.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.
3) 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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Replace the front oxygen (A/F) sensor. 
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Repair the ground short circuit of harness between ECM and front oxygen (A/F) sensor connector.
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