# P0420 code, looking for input please...



## hosic (Mar 20, 2012)

Hey guys, just looking for some help.
I have a 06 4L 4x4 and i have the CEL on with a p0420 code. I know its for bank 1 front cat or o2 sensor. 

The vehicle seems to run ok, has a slight rough idle now and also can now rear a slight hissing from drivers side engine area.

I have a scanner and read all 4 o2 sensor values. 3 out of 4 are reading .3V, the other was .6V. Does that .6 raise a flag or is that ok?

From some reading it seems the CAT is always a problem with these trucks.
What my concern is im in arizona but was told I HAVE to buy a cat thats california emission ready due to a number in my VIN. Is that true or can I get away with one thats not california ready being i dont live there?

Thanks!


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## jaf06se (Apr 26, 2012)

Unless you plan to move to Cali I wouldn't worry about it. Your VIN shouldn't have anything to do with an exhaust fix. Was it a stealership that told you that? Check out courtesy parts.com to order a new OEM one or go to a parts store and pick up an aftermarket one. The emission ones aren't necessary unless you have to have your truck inspected.


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## SPEEDO (Jun 9, 2003)

how many miles?? I am pretty sure the cat carries a 8yr/80,000 mile warranty on them...


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## smj999smj (Jan 1, 2006)

You'll need to go by your state's emissions regulations. In California, a catalytic converter, or almost any part replacement or modification that would affect emissions, needs to be "CARB" certified. In just about every other state, you can use any aftermarket part regardless of the emissions certification of the vehicle and regardless if the replacement part is CARB certified or not. Your DMV should be able to provide you with an answer.

In almost every P0420/430 DTC setting I see, so long as it is without another DTC in the ECM memory, the catalytic converter is the fault. One thing you'll want to do is inspect the inlet side of the catalyst for any signs of deterioration or broken substrate or signs of oil burning. If all looks good, just replaced the catalytic converter. If there is signs of deterioration of the substrate, but no signs of oil burning, I would replace both sides if the other side is original, as well. If there are signs of oil burning, then you may have scored cylinder walls due to catalyst substrate deterioration and ingestion of the catalyst material into the cylinders. Much like the 02-04 Altima QR25DE's, there have been a few reports of R51 Pathfinders burning oil due to this, which is caused by an EGR system that uses the variable valve timing to open the exhaust valve slightly during an intake cycle to draw in inert gas from the exhaust system, rather than using a convention EGR valve system to do it. If your original catalytic converter failed because of this, then the replacement converter will eventually do the same thing unless the issue is addressed, usually meaning engine replacement or at least honing and re-ringing, not a cheap nor easy job on a VQ-series.


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## azrocketman (Oct 5, 2005)

hosic said:


> Hey guys, just looking for some help.
> I have a 06 4L 4x4 and i have the CEL on with a p0420 code. I know its for bank 1 front cat or o2 sensor.
> 
> The vehicle seems to run ok, has a slight rough idle now and also can now rear a slight hissing from drivers side engine area.
> ...


I would concentrate on the hissing sound first. You may have a vacuum leak that is responsible for the rough idle (and throwing a code).

Steve


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