# P0420 Help



## Brianz01Altima (Jan 17, 2007)

I have a 2001 GXE with 162k and got my first ses light. When I pull the code it is P0420 (catatyst efficiency below threshold). The light will stay off for 1000 to 600 miles before it comes back on.

The car idles great and has engine has been well maintained. I have checked for exhaust leaks, injector leaks and the plugs/ wires, all is good.

I still need to check for intake gasket leaks, could this be the cause? or could the catalytic conveter really be going out.

Thanks for your help, this looks like a great site....


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## metro273 (Sep 16, 2005)

If I'm right, your cat is "bad". I've replaced 2 of these already in the L30 Altimas in the past 6 months. This is an easy diagnosis if you are able to watch the voltages of both the front and rear O2 sensors...


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## KA24Tech (Feb 2, 2004)

I would first check for a slow responding or "lazy" rear O2 sensor before replacing the cat. I have found a few O2 sensors causing the P0420. Of course if it reacts normally then the cat would be the obvious fix.

Troy


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## Brianz01Altima (Jan 17, 2007)

Thanks for the replies. I'll look closer at the O2 sensors. Buy the way, I've heard that O2 sensors have a limited life and should be replaced after a certain amount of miles... Do you guys agree with this. Mine have never been replaced and my gas mileage is as good as ever..........


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## KA24Tech (Feb 2, 2004)

Only the front O2 has to do with ECM controlling the fuel trim. The rear is mainly for emissions and the one that will trigger a P0420. There is no recommended service interval from Nissan on the O2 sensors. However, the manufacturers of the sensors suggest every 60k - 90k miles.

Troy


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## Brianz01Altima (Jan 17, 2007)

I replaced the cat and my problem is solved. I just wanted to put some many miles on the car before I spoke too soon............


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## stancho (Aug 26, 2006)

My wife's 2000 Altima had the same problem last fall at 78k miles. Being an emissions component it is warranted until 80K. One dealer tried to charge me $400 to replace the O2 sensor. I laughed and later replaced it myself which didn't help. Second dealer acknowledged a bad cat and replaced it.


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