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P0420 on Pathfinder - Catalyst System Efficiency Below Threshold Forums > > P0420 on Pathfinder - Catalyst System Efficiency Below Threshold P0420 on Pathfinder - Catalyst System Efficiency Below Threshold
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Old 12-03-2017, 09:20 AM
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Default P0420 on Pathfinder - Catalyst System Efficiency Below Threshold

Hi guys,

I have 2002 Pathfinder LE with 160k miles. Always maintained well; original owner. I'm getting P0420 and my mechanic whom I trust and have known for 10+ years says that cat will likely needs to be replaced but we can wait until smog time comes.

I'm a software guy and I have no clue about cars but I logged OBD data for a month or so (BT dongle and my phone) to see what I can make of any trend.

The only observation I can make is that my O2 (same bank x1 as the cat failure code) sensor voltage jumps sporadically between .1 and .8 volts every 15 seconds or so in a very consistent pattern regardless of vehicle status; speed; temperature; etc

What do you guys make of this? Obviously I am hoping to skip a $1k worth of repairs which is what I hear cat replacement might cost me.

Thanks
~B
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Old 12-11-2017, 07:01 AM
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Voltage is supposed to range anywhere between 0 volts to about 1 volt on a given oxygen sensor. This shows the rich to lean cycling pattern of the sensor. The ECM compares the frequency of the cycling between the front and rear sensors on each bank, which set in front of and behind the upstream catalytic converter. An efficiently working catalytic converter will see during cruising conditions an approximate ratio of 2:1 for the number of cycles of the front sensor compared to the number of cycles of the rear sensor. If the ratio is close to 1:1, then the converter is not efficiently working at breaking down the exhaust gases and the ECM will trigger a code. Sometimes you can "fake out" the ECM by installing a spacer or "CEL eliminator" at the rear sensor, which pulls the rear sensor element partially out of the exhaust stream to give it a false reading.
In most cases when there is a P0420/P0430 code and no other codes, no exhaust leaks, no intake leaks and the engine is running normally, it is typically the catalytic converter, itself, that needs to be replaced to fix the problem. If you don't live in a state that mandates California-style emissions inspections, you can purchase an aftermarket converter which is significantly less-expensive that a genuine Nissan part (Rockauto.com is a good source; I've had good luck with Walker converters).
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Old 12-11-2017, 06:19 PM
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Thanks, sadly I am in California so will just have to bite the bullet. Thank you for clarifying how the logic flows for this code. It makes perfect sense. I don't be fiddling with the washer magic :)
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Old 12-11-2017, 09:06 PM
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Yeah, the CEL eliminator nor spacer won't fly in CA and neither will most aftermarket catalytic converters, unless the are C.A.R.B. certified.
A quick visit to Rockauto.com shows the following C.A.R.B. options for a right-side bank, upstream catalytic converter for a 2002 Pathfinder:

Eastern Catalytic # 650517 $211.79
Walker # 81754 $240.79
*Prices don't include shipping nor any gaskets that may be required. You (or anyone else) can use the following discount code for 5% off if you want until 01/14/2018:

7289060657999262
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