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Home >> Toyota >> 2000 >> Avalon XLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics >> Diagnostic Tests >> DTC P0420: Catalyst System Efficiency Below Threshold >> Diagnosis & Repair
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Diagnosis & Repair

  1. If other DTCs are displayed, diagnose and repair those DTCs first and retest system. If only DTC P0420 is 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 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 NO. 2 CIRCUIT . If problem exists, repair as necessary. If problem does not exist, replace catalytic converter.
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