Catalyst system monitoring method for internal combustion engine of vehicle, involves determining catalyst state code value based on amount of NOx present in exhaust gas corresponding to rich and lean air fuel ratio

摘要

The amount of NOx present in the exhaust gas corresponding to rich and lean air fuel ratio are determined. Several catalyst state code values such as KZKKZ, KZKMM, KZKMA indicating NOx discharge, NOx emission and HC emission are determined based on the determined NOx value.