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DTC P0421:00: Notes

DTC P0421:00 (L3 WITH TC) DETECTION CONDITION & POSSIBLE CAUSES

DTC P0421:00 Warm up catalyst system efficiency below threshold
DETECTION CONDITION 
  • The PCM compares the number of A/F sensor and HO2S inversions for a predetermined time. The PCM monitors the HO2S inversion ratio when the following conditions are met. The PCM detects the inversion ratio. If the inversion ratio is below threshold, the PCM determine that the catalyst system has deteriorated.

  • The A/F sensor inversion ratio is as prescribed when the following monitoring conditions are met:
  • The accumulated occurrence time of the following monitoring conditions has exceeded the prescribed time limit:

MONITORING CONDITIONS 
  • Engine speed: 1, 500-3, 250 rpm 
  • Calculated TWC temperature: above 400°C {752°F} 
  • Absolute load: 20-48%  (at engine speed 2, 000 rpm  )

Diagnostic support note 
  • This is an intermittent monitor (catalyst).
  • The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM.
  • PENDING CODE is available if the PCM detects the above malfunction condition during first drive cycle.
  • FREEZE FRAME DATA (Mode 2)/Snapshot data is available.
  • The DTC is stored in the PCM memory.
POSSIBLE CAUSE 
  • Exhaust gas leakage
  • A/F sensor loose
  • HO2S loose
  • TWC deterioration or malfunction
  • PCM malfunction
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