Circuit/System Description
A 3-way catalytic converter (TWC) controls emissions by converting hydrocarbons (HC) and carbon monoxide (CO) into CO2, and oxides of nitrogen (NOx) into nitrogen. The TWC also stores oxygen. The control module monitors this oxygen storage capacity by comparing the pre and post-catalyst oxygen sensor signals while adding and subtracting fuel during specific idle conditions. The control module compares the engine and catalyst oxygen sensor signals in order to determine if the oxygen storage capacity of the catalyst is degraded.
IMPORTANT:
A new converter with less than 100 miles on it may set P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.
If the ECM detects the degraded condition DTC P0420 sets.