DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)
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DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW
THRESHOLD (BANK 1)
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CHECK ANY OTHER DTC ON DISPLAY.
Is any other
DTC displayed?
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Inspect the relevant DTC
using “List of Diagnostic Trouble Code (DTC)”.
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Note
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In this case, it is not necessary
to inspect DTC P0420.
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CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR.
Turn the ignition switch to OFF.
Disconnect the connectors from ECM and rear oxygen
sensor.
Measure the resistance of harness between ECM and rear
oxygen sensor connector.
Connector & terminal
(B137) No. 24 — (B19) No. 3:
(B136) No. 35 — (B19) No. 4:
Is the resistance less than 1 Ω?
Repair open circuit in harness between
ECM and rear oxygen sensor connector.
CHECK HARNESS BETWEEN REAR OXYGEN SENSOR AND ECM CONNECTOR.
Measure the resistance between rear oxygen sensor harness
connector and chassis ground.
Connector & terminal
(B137) No. 31 — Chassis ground:
Is the resistance less than 1 Ω?
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Repair harness and connector.
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Note
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In this case, repair the following:
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Open circuit
in harness between rear oxygen sensor and ECM connector
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Poor contact in rear oxygen sensor connector
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Poor contact in ECM connector
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CHECK EXHAUST SYSTEM.
Check for gas leaks or air suction caused by loose or dislocated
nuts and bolts, and open hole at exhaust pipes.
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Note
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Check the following positions.
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Between
cylinder head and front exhaust pipe
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Between front exhaust pipe and front catalytic converter
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Between front catalytic converter and rear catalytic
converter
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Is there a
fault in exhaust system?
Repair or replace the exhaust
system.
CHECK CATALYTIC CONVERTER.
Is there damage
at rear face or front face of front catalyst?
Replace the catalytic converter.
Contact Service Center.
