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Diagnosis & Repair

WARNING: This page is about a different car, the 2002 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
  1. If other DTCs are displayed, diagnose and repair those DTCs first and retest system. If only DTC P0420/P0430 are displayed, go to next step.
  2. Check exhaust system for leaks. If problem exists, repair as necessary. If problem does not exist, go to next step.
  3. Check A/F sensor No. 1 and No. 2 circuits. See DTC P0125: INSUFFICIENT COOLANT TEMPERATURE FOR CLOSED LOOP FUEL CONTROL . If problem exists, repair as necessary. If problem does not exist, go to next step.
  4. Check heated oxygen sensor No. 2 circuits. See DTC P0136: HEATED OXYGEN SENSOR CIRCUIT (BANK NO. 1, SENSOR NO. 2) & DTC P0156: HEATED OXYGEN SENSOR CIRCUIT MALFUNCTION (BANK NO. 2, SENSOR NO. 2) . If problem exists, repair as necessary. If problem does not exist, replace catalytic converter.
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