P0421

DTC P0421 Catalyst(MCC) Deterioration (Bank 1)

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

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

Troubleshooting Guide:

Test Procedure: