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Home >> Toyota >> 1999 >> Celica 2D Convertible, Standard >> 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 any other DTCs are displayed, diagnose and repair those DTCs first. 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 oxygen sensor No. 1. See DTC P0130: OXYGEN SENSOR NO. 1 CIRCUIT . If problem exists, repair as necessary. If problem does not exist, go to next step.
  4. Check oxygen sensor No. 2. See DTC P0136: OXYGEN SENSOR NO. 2 CIRCUIT . If problem exists, repair as necessary. If problem does not exist, replace catalytic converter.
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