# Cause of P0420 on 2002 Pathfinder



## dsurls (Sep 8, 2013)

I've had P0420 on and off the last couple of months, indicating an inefficient catalytic converter on Bank 1 (passenger side). So, I've been doing some research to determine the culprit of the problem, and I've run diagnostics using my OBDWiz software scanner.

If you look at the attached graphs, you can see a recent scan of the waveforms for the O2 sensors and the Short term Fuel % Trim values for both banks. Before running the scanner, I reset the code (only P0420 was showing) and ran drive cycles to get it ready for emissions testing. I ran the vehicle at idle at about 750 rpm for about 5 minutes, then at 2750 rpm for about 5 minutes, then back to 750 for about 2 minutes.










































My initial take on these graphs is that the values look OK. I'm certainly not an expert, but the short term trim values seem reasonable on both banks. If anything, it looks like perhaps the downstream Bank 2 O2 sensor could be mirroring the upstream sensor a little too much, but it seems to settle down. But the Bank 1 values look pretty good, which is where I would expect to see mirroring with the P0420 code.

So, the question is, can anyone see anything wrong with these graphs that would signal a potential problem?

BTW, the vehicle is currently at about 175K miles, with a rebuilt engine at 160K. The catalytic converters are original.

Thanks for any suggestions you might have!


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## smj999smj (Jan 1, 2006)

It's kind of hard to compare the rich to lean frequencies of two sensors as accurately or efficiently as an ECM. The fact that the signals due appear to mirror each other at times could be the issue. The ECM looks for an approximate ratio of 2:1 when comparing the upstream to downstream sensors. A ratio close to 1:1 would indicate the catalyst substrate is not doing its job of breaking down exhaust emissions. In my experience, unless you have exhaust leaks or other codes besides the catalyst codes (ie O2 sensor codes, MAS codes, etc.) and there are no vacuum leaks and the fuel pressure is within spec and there are no TSB's for the code, the catalytic converter needs to be replaced. Inefficient catalytic converters are certainly not unheard of on Nissans!


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## p3210 (Jan 7, 2012)

I have a 2001 PF with 205k on it (motor and cats are original).
Ive gotten hit with both P0420 and P0430. 
With 205K and rust forming at the wheel wells I figure I wont be keeping this Pathy many more years :-(
I hesitate to put this out there cause I know the right thing would be to change the cats out (and I might just do that!).
But, with the hopeful goal of getting it thru inspection and getting my DMV sticker for another 2 years ... I've found that adding techron (chevron gas additive) will turn the P0420 related Check Eng Lite off. But keep in mind the problem isn't fixed. Once I go back to non-techron laced fuel the CEL turns back on. (Plus - using techron on a frequent basis I might be doing some damage to the vehicle)
If you're looking to get your pathy thru inspection... its a potential option. If you're looking for a permanent fix; this would not be it.
Best of luck with your Pathy!


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## smj999smj (Jan 1, 2006)

P3210...Have you had the recall performed on your 2001 for the strut tower corrosion issues?


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## p3210 (Jan 7, 2012)

Yep. Had it done a year or 2(?) ago.
Not sure what they did, but I dropped it off to Nissan ... when I picked it up they said they fixed the problem.


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