Code po 420
 

Odds are its the converter. However check the items in the link below first.

The Misleading Nature of the PO42O Code - Eastern Manufacturing

Before you spend some big dollars change out the Air/Fuel O2 Oxygen sensor upstream. Only costs $55 and is very simple to do since it's the one right in front when you open the hood.

I understand, its hard to work out there. I'm in Illinois. Never seen so much cold weather.

Start simple


Do nothing if it does not affect performance. No emissions testing.
Check everything plugs, air filter, gas filter, etc. Is everything well maintained.

Reset code and go from there.

Check idle air control valve. Mine was filthy. Use CRC 05078 Throttle Body & Air‑Intake. Google on how to. Fixed many code issues on my vehicles.
Hope that helps.

I wanted to add one more thing . Just because you have a code does not always bring you to the root cause. Codes are a guide not necessarily a solution. My opinion.

I got that code on my 02. The mechanic said try putting a full bottle of Sea Foam in the tank and fill it up with 92 octane and give that a try. He cleared the codes and off we went. No code showing up for a year. Two weeks ago it showed up again and I did the same thing. No more codes.


He felt it could be some bad gas and a little more cranking in the winter time (richer mixture) not completely getting burnt. He said all it will cost is $8 and to give it a try. Can't hurt. Well, we saved a bunch of $$$ and thanked the mechanic. Give it a try.

Thanks for the information!