Step 1 – Resolve Engine Trouble Codes The first step is to resolve any other codes that may have come up in addition to the P0420; especially troublesome is the P0300 series of cylinder misfire codes. A P0300 code could be related to something in the ignition (spark plug or coil), th...
It just runs the engine lean for so many seconds to bank up some oxygen in the cat, and then rich for so many seconds to see how long the cat can still do its job. The ones that can't make the grade set the code. #9 ChapmanF, Dec 20, 2023 Pioneerscot likes this. ...
Plus, if your check engine light is on for a P0420 code and you decide not to fix it, another more serious code could be triggered and you'd never know. The MIL lights up whether you have one code or ten! While I have your attention, don't forget to do oil changes as the ...