1.CHECK POWER SUPPLY TO FRONT OXYGEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from front oxygen (A/F) sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between front oxygen (A/F) sensor connector and engine ground.
Connector & terminal
(B379) No. 1 (+) — Engine ground (−):
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Is the voltage 10 V or more?
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Repair the power supply line.
NOTE:
In this case, repair the following item:
• Open circuit in harness between A/F, oxygen sensor relay and front oxygen (A/F) sensor
• Poor contact of A/F, oxygen sensor relay connector
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2.CHECK HARNESS BETWEEN ECM AND FRONT OXYGEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from the ECM.
3) Measure the resistance between ECM and front oxygen (A/F) sensor connector.
Connector & terminal
(B136) No. 3 — (B379) No. 2:
(B136) No. 2 — (B379) 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 front oxygen (A/F) sensor.
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3.CHECK GROUND CIRCUIT FOR ECM.
Measure the resistance of harness between ECM and chassis ground.
Connector & terminal
(B134) No. 5 — Chassis ground:
(B137) No. 1 — Chassis ground:
(B137) No. 2 — Chassis ground:
(B137) No. 3 — Chassis ground:
(B137) No. 7 — Chassis ground:
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Is the resistance less than 5 Ω?
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Repair the harness and connector.
NOTE:
In this case, repair the following item:
• Open circuit of harness between ECM and engine ground
• Poor contact of coupling connector
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4.CHECK FRONT OXYGEN (A/F) SENSOR.
Measure the resistance between front oxygen (A/F) sensor terminals.
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Is the resistance between 2 — 3 Ω?
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Repair the poor contact of the ECM connector.
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Replace the front oxygen (A/F) sensor. 
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