Diagnostic apparatus for exhaust gas clarification apparatus for internal combustion engine

摘要

A diagnostic apparatus for exhaust gas clarification apparatus for internal combustion engine diagnoses the individual catalyst independently by an air/fuel ratio sensor mounted before and after the individual catalyst. The individual catalyst is diagnosed by estimating the correlation of the output signals from the air/fuel ratio sensors mounted before and after the individual catalyst. The individual diagnosis operation is performed at distinctive operation regions adequate for their corresponding diagnostic mode. A by-pass route is provided for by-passing the exhaust gas from the upstream catalyst, and a by-pass valve switches the exhaust gas flow into the upstream catalyst or into the by-pass routes. A cross-correlation function calculation valve based upon outputs from air/fuel ratio sensors permits diagnosis of degradation of the overall catalyst.