Circuit/System Description
WARNING: This page is about a different car, the 2011 GMC Yukon, 2011 Chevrolet Tahoe, and 2011 Cadillac Escalade. However, it is still accessible from the selected car via links, so may be relevant.
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.