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I just had the first CEL in my reliable grocery getter.
I have an 11 1.8 versa with 140k miles on it.

I am going to jack up the car tonight and measure the voltages from the sensors to see what we are getting.

Anyone have any tips for this? Usually i can narrow things down to a few inexpensive parts and use my shotgun approach and usually fix it. This however is no such issues. The full exhaust "mid pipe" with 2 cats is 325 at oriley's a couple of flanged connections and we would be all set.... or what im hoping is the problem would be one of the O2 sensors.

Does anyone have any experience with this?
I have an ODBII reader that is picking up one of the O2sensors but not the other.
After doing some reading, this is common. Something to do with PID adresses? IDK.

Any info would be appreciated.
 

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Is this a California car?

If it were me and the test came back as okay for the sensor, I would buy a spark plug defouler, install it with the downstream 02 sensor, unhook the battery for a few minutes, and drive around. If the CEL stays off, I would leave it and call it good. Otherwise, you can get a generic plug and play o2 sensor for $30 on eBay or $65 for a Walker brand on RockAuto.

What do you mean by picking up one but not the other? In general terms, the 2nd o2 sensor is just verifying the cat is working and putting out emissions as it should..... The primary o2 sensor actually provides feedback to the ECU and has it adjust the air to fuel ratio and is far more important (in my opinion) than the 2nd sensor.
 

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I don't live in California. I replaced the spark plugs less than a year ago. So, I'm skeptical that they are the issue. I recently had the fuel pump replaced because it died. The air filter is less than a 6 months old.

It is consuming a lot of fuel now, but that is more or less expected with the CEL if an O2 sensor is malfunctioning right?
 

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I don't live in California. I replaced the spark plugs less than a year ago. So, I'm skeptical that they are the issue. I recently had the fuel pump replaced because it died. The air filter is less than a 6 months old.

It is consuming a lot of fuel now, but that is more or less expected with the CEL if an O2 sensor is malfunctioning right?
I asked because alot of California cars have different catalytic converters to meet their more stringent emissions laws.
I can't remember if these cars have inline fuel filters, but if they do that should be changed out as well.

Yes, high fuel consumption is generally caused by the primary o2 sensor failing. Because the ECU can't get measurements from the o2 sensor, it is going to make the car run rich (safety default) in order to prevent it from running lean and damaging the internals.
 

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I can't remember if these cars have inline fuel filters, but if they do that should be changed out as well.

I just had the entire fuel pump/filter unit replaced last week. I doubt that its that. I cleared the code yesterday and it hasn't come back. If there are any changes, I'll post again.

Thanks for the feedback.
 

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I just had the entire fuel pump/filter unit replaced last week. I doubt that its that. I cleared the code yesterday and it hasn't come back. If there are any changes, I'll post again.

Thanks for the feedback.
That is a filter sock for the fuel pump to prevent it from picking up bigger sediment at the bottom of the tank like rust which would result in damage to the pump. Usually there is a inline fuel filter closer to the injectors that will screen out the very fine impurities.

Edit: Nevermind. Looks like the filter is in with the pump and not further down the line!
 

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So, the Code P0420 keep coming back after I clear it. It doesn't come back immediately. I cleared it this morning. So, I expect to see it back in two or three days. Does this indicate that the root cause it closer to an O2 sensor issue or a catalytic converter issue? Is is even possible to distinguish one from the other? Can you check Ohms across the sensor to determine whether or not the sensor has gone bad?
 
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