P0421

DTC P0421 Catalyst Circuit Malfunction-MCC Deterioration (Bank 1)

DESCRIPTION

The ECU compares the waveform of the front HO2S with the waveform of the rear HO2S to determine whether or not catalyst performance has deteriorated. Air-fuel ratio feedback compensation keeps the waveform of the front HO2S repeatedly changing back and forth from rich to lean.

If the catalyst is functioning normally, the waveform of the rear HO2S switches back and forth between rich and lean much more slowly than the waveform of the front HO2S. When both waveforms change at a similar rate, catalyst-performance has deteriorated.

DTC Detection Condition:

TEST PROCEDURE