# DTC Codes: P0420 and P0430



## sadatay (Nov 22, 2005)

Hello All...

New to the forum.....

I have a question regarding my 2001 Maxima SE. It has 162,000 almost trouble free miles.

My check engine light is on, and I am getting Codes: P0420 and P0430, *Catalyst Efficiency below Threshold Banks 1&2*

The dealer says I have to replace both catalytic converters and all FOUR O2 sensors. That runs almost $2800 total...  

I really don't think its the catalytic converter because she's running strong as ever and I have not smelled the "sulfur" smell as i've read from the other posts.

Anyone might know how I can begin to trouble shoot this??

Much Appreciated!


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## brianw (Feb 25, 2004)

Wow, is the dealer including a lube job with that?

More likely it's just o2 sensors that are getting old. Should be $100-150 a pop if you use genuine Nissan replacements. $15 for a 22mm open-end wrench and $3 for some anti-seize compound... then do it yourself.


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## Puppetmaster (Mar 28, 2005)

I agree with Brian.... do the O2s yourself and see what happens. 

Use this the diagrams in this TSB as a guide: 

http://maxima.theowensfamily.com/tsb/NTB02-051a.pdf

Additionally, the FSM lists some other possible causes that you can check: 

Exhaust tube
Intake air leaks
Injectors
Injector leaks
Spark plug
Improper ignition timing


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## Puppetmaster (Mar 28, 2005)

Just to add one more thing, the 420 and 430 codes are for both pre-cats. If they go bad, you won't necessarily smell anything because the main cat will still be able to take care of that. 

I'm beginning to doubt the O2 sensor replacement as a fix, but I know for sure that an O2 simulator to trick the ECU will work as a quick (and cheaper) alternative to replacing the pre-cats. You can read more about em at www.o2sim.com. 

Alternatively, you could get aftermarket headers and do away with the pre-cats altogether, it'll be cheaper than getting new pre-cats and you'll get about an extra 20 whp to play with.


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## tcostanz (Nov 14, 2007)

be careful, replaced to downstream o2 sensors and the light came back. the quality of nissan is deteriorating. i have a feeling the cats are bad. but in any case even if you have to replace the cats the o2 sensors first this is the first time that i will have to change the converters. 95 % the o2's worked


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## tcostanz (Nov 14, 2007)

hello, i am wondering, i have changed both downstream oxygen sensors, in 2 different nissans, 1 maxima and 1 sentr. the one in the sentra somebody changed the converters and the upstresn o2 sensoer. i was wondering on both nissans, i only saw the engine temperture get to 176 degrees farenhieght. i have not seen the cars again but my next step is change the thermostat and see if i can get to 190 or higher. i am worndering if the car is running a slight rich from the cooler temperture. if you change the thermostat and the problem solve please post it


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