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DTC Detecting Condition and Trouble Area

DIAGNOSTIC INFORMATION AND PROCEDURES REFERENCE CHART

DTC detecting condition Trouble area
P0420: Catalyst System Efficiency Below Threshold 
Ratio of integrated value of HO2S output variation per integrated value of A/F sensor output variation is out of specified range while vehicle is running after warmed up.
(2 D/C detection logic)
  • Exhaust gas leak
  • HO2S and/or its circuit
  • A/F sensor and/or its circuit
  • TWC
  • ECM