Circuit/System Description

A 3-way catalytic converter controls emissions by converting hydrocarbons and CO into CO2 and oxides of nitrogen NOx into nitrogen. The 3-way catalytic converter also stores oxygen. The ECM monitors this oxygen storage capacity by comparing the pre and post-catalyst oxygen sensor signals while adding and subtracting fuel during specific deceleration fuel cut-off conditions. The ECM compares the pre and post-catalyst oxygen sensor signals to determine if the oxygen storage capacity of the catalyst is degraded.