Finding P0420 on a specific vehicle can be researched using blended service info. This video is sponsored by Mitchell 1.
Engine management systems compensate for changes in engine speed, loads and temperatures by adjusting the amount of fuel injected, spark advance/retard and even when the intake and exhaust valves open. These adjustments can only do so much. Tailpipe emissions are cut further by exhaust gas recirculation (EGR) and secondary air injection systems. The last line