Does my catalytic converter need to be replaced or not?

Asked by Oct 29, 2015 at 09:28 AM about the 2009 Nissan Altima 2.5 SL

Question type: Maintenance & Repair

Almost 2 weeks my service engine soon light came on after filling my tank
with gas but it wasn't blinking. I took it to Auto Zone and they told me the
Catalytic converter(P0420) needed to be replaced after testing it with a
machine. Well this morning i filled my tank with gas and noticed before
even driving off that the service engine soon light was gone. At this point I
dont Know what to do. I'm thinking maybe I used some bad gas when I
originally filled my tank 2 weeks ago. Should I be concerned?

1 Answer


A code P0420 may mean that one or more of the following has happened: Leaded fuel was used where unleaded was called for A damaged or failed oxygen sensor (HO2S) Downstream oxygen sensor (HO2S) wiring damaged or connected improperly The engine coolant temperature sensor is not working properly Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe Retarded spark timing The oxygen sensors in front and behind the converter are reporting too similar of readings Leaking fuel injector or high fuel pressure Cylinder misfire Oil contamination So bad fuel can also cause this code, I would run a can of seafoam in the fuel to get things cleaned up, then on you next fill up use Chevron or Texaco, that fuel contains Techron and it will help to keep your fuel system and injectors clean, if you can't get Techron fuel then you can buy some at your local parts store. So that should take care of the bad fuel issue, and hopefully it didn't damage the catalyst, I would not be too concerned at this point as the light went out on it's own that means that the problem has not reoccurred in at least 20 restarts. HTH

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