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have a p 420 code upstream bank 1 o2 sensor i replaced the o2 with a new one code came back after a short drive i also replaced the maf senor i also have the down stream bank2 o2 senor but not have put it in any input will help
 

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my mechanic told me once about this code, usually it is the catalytic converter failing...but usually that fails because of something else (misfire, car running lean etc etc)
You should check that to begin with.
 

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2016 Nissan Versa S (manual transmission)
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I've had two (GM) vehicles (in the past) throw P0420 codes. In both cases, it was the catalytic converter. The first time, I went down the rabbit hole of trying a downstream O2 sensor and tested other items, but at the end of the day it was the catalytic converter. The second time, I just ordered up a catalytic converter.

Unless you are in a CARB requirement state (like California or New York), I suggest looking on ebay for a replacement cat. I saved A LOT of money ordering on-line. Also check to make sure gaskets are included.

In both cases, replacing the catalytic converter was easy... just a few bolts on each end and re-installing the downstream O2 sensor (with a very small amount of anti seize on the threads of the O2 sensor).

Best of luck.
 

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Funny, I was just about to post with the same issue - p420 code. When I bought it, the dealer mentioned they had cleared the code after they fixed an exhaust leak, cleaned "the O2 sensor", and thought they fixed it.

Trying to use the OBD to read the O2 sensors and see if it really is the cat or the sensors - or alternatly, fins what is killing the cat in the first place.

Anyone know what the difference between the O2 sensors is supposed to be? I've been comparing the outputs between my '10 w/ the code and my '08 w/o the code. They seem similar,

When it's warmed up and the pedal is down, I get a "jagged" toggle between .1 and .9 on the upstream, and about .24 steady on the down stream, which seems expected. The weird thing is when coasting under power, the voltage on the upstream drops to 0, but the downstream suddenly jumps up. Anyone know if that is normal?
 
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