po420 po430

[cloudy6969]

04 pathfinder with a code po420 and po430 I kinda have an idea what they are just dont know were to start I sure dont want to repalce the cat(s) if i dont have to and it has 4 o2 sensors not sur witch one(s) are bad please help!!!

[Towncivilian]

Your cats are operating below efficiency. Replacement of the post-cat O2 sensors very rarely fixes the P0420/P0430 codes. How many miles do you have on this Pathfinder? Does it burn a lot of oil?

[cloudy6969]

It has 155000 and yes it does burn oil about 1qt 1000 mil or so ,already had engin replace at 78000 from dealer about don't know how many are on this one.And the mpg is not so good

[Towncivilian]

That would be why your cats are failing. Why was the previous engine replaced? Was it burning oil as well?

Possible causes of your oil burning are the passenger side valve cover (see here), or a power valve screw got loose and got sucked in by the engine and caused engine damage.

[cloudy6969]

the other engine was burning it and blowing smoke.So were do think i should start with this one lol

[Towncivilian]

Are you mechanically inclined? You can check the status of the power valve screws yourself. Follow this guide. Put red threadlocker on all of the screws. If any are missing, that's definitely a possible cause of your oil consumption and/or catalytic converter issues. While you have the upper and lower intake manifolds apart, replace the PCV valve with an OEM part (shouldn't be more than $16 or so). If you're confident that you can do this yourself, let me know and I'll compile a list of the necessary gaskets you'll need to replace.

[cloudy6969]

yes i'v turned a few wrenchs in my day but I'm more worried about geting the check engine light off so it will pass then do the other work when i have a little more time.The cats that i would have to replace are the ones comming off the engine?Becuse it looks like there are two more after that.

[Towncivilian]

The two "cats" after the cats are resonators. People often mistake them for catalytic converters.