What does PO420 code mean? Catalytic Converter Problem

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The code P0420 is a code given off the vehicle due to catalyst efficiency.  The diagnostics given from the computer is reading that the post catalytic converter O2 sensor has too much activity going on. The catalytic converter's job is to reduce the nitrogen oxide, carbon monoxide and unburnt hydrocarbons, by converting it into carbon dioxide and water when the exhaust air passes through your catalytic converter.  The post cat O2 sensor will read the O2 content in the exhaust and if it moves up and down too much or too high and low, the computer interprets that the cat is not ridding the exhaust of its pollutants.  The problem could be a bad cat, O2 sensor (Pre- and/or post cat) or O2 sensor wires, or an air fuel mixture problem that has caused the cat to fail.   
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