Hi, there is a problem with the efficiency of the catalytic converter not working
properly. First check ,clean the oxygen sensors or replace them when faulty. Also
check the catalytic converter. For good instruction visit Google,you tube for repair
instruction videos.

Hi,how many miles is there on this car? Sometimes when the engine has more than
normal oil consumption ,this can be the cause of the 420 because the catalytic
converter is polluted or burned, and does not operate as it used to do.