Before anyone directs me to the search bar of the forum, I want to inform everyone that I did use it but I'd still like to share my story and why I am still completely perplexed by this situation.

I bought a 2008 G35x Sedan (currently 53k miles) from a salvaged auction and had it repaired. The car was rear ended and I did have to replace the back clip and the exhaust (replaced with OEM catback).

Since I received the car I've been receiving P2A00 codes but here is the catch. The CEL turns off on it's own (sometimes for long periods of time) and I was able to PASS emissions with it. CEL was off but P2A00 code was stored as indicated on the emission document which surprised even my local mechanic that the car managed to pass. I did replace one of the upstream sensors but the CEL still continues to show up. I bought an bluetooth OBDII computer so now I can scan it myself and turn off the code myself manually (using Torque app) and the most recent code was again, P2A00 Bank 1 Sensor 1. Another part that adds to the confusion, is that I get about spot on gas mileage as advertised which is 17/23. I'm currently averaging 19 driving through winter and Chicago's heavy morning traffic.

SUMMARY:
The car is clearly not on warranty so I want to forget about the dealership because they are going to charge me about a grand minimum to fix this. Can it really be a bad O2 sensor when I get ideal gas mileage, passed emissions, and shows up on a rare occasions? If I get ideal gas mileage can it really be fuel pressure or fuel injector problem? (Car runs perfectly fine). I predict it's not an exhaust leak either because normally, even with small leaks, you can hear it from inside the car.

Here is the list I noticed everyone mentions but again, they don't SEEM to be an issue. Any other issues you guys might predict that could lead to this code?

- Air Fuel Ratio (A/F) Sensor Bank 1 Sensor 1
- Air Fuel Ratio (A/F) Sensor Bank 1 Sensor 1 harness is open or shorted
- Air Fuel Ratio (A/F) Sensor Bank 1 Sensor 1 circuit poor electrical connection
- Fuel pressure
- Fuel injector
- Intake air leaks

Read more: http://engine-codes.com/p2a00_nissan.html#ixzz2JObFFcaB

Thank you for any assistance.

EDIT
I recall a dealer telling me that they reprogram the ECU when they install a new O2 sensor. I had two separate mechanics tell me that's a load of crap and the ECU automatically detects a new O2 sensor without needing to program anything. Can anyone comment on that?

EDIT2
Went to fill up and I figured I'd run the vehicle test portion of the torque app and I made these screenshots once they got back (car got plenty of time to warm up). I don't know if this helps any. Keep in mind this is now 4 days after I reset the code manually and I drove at least 150 miles by now.

http://i50.tinypic.com/1zfrd5g.png
http://i48.tinypic.com/2qvw7qh.png
http://i49.tinypic.com/15i6l2o.png
http://i45.tinypic.com/20kswhh.png

 

When changing 02 sensors you're supposed to take the negative battery cable off the battery for two minutes to clear the learned operating values of the old sensor from the powertrain control module.

Anytime you disconnect the negative cable from the battery you have to do the resets for the idle air volume learning, throttle valve closed learning and accelerator pedal released position learning procedures.

I think these resets are what the dealership meant when they told you they have to reprogram the ecu, if they charge you to do this tell them to f off and you'll do the pedal resets yourself for free.

This is what the Haynes manual says to do...not the f off part.-lol Give it a try and see if it clears the phantom codes.

 

I'll give it a shot and report back if this reoccurs! However, the O2 sensor was replaced a year ago so I'm not sure if that will make any difference. Still, never had the battery die on me so there might be a small chance it still hasn't cleared those values. My next idea is to switch the two upstream sensors with each other and see if I get a code for the other one. I figured at the same time I can test if the O2 sensor connection isn't secure and that's why it turns on so rarely (connection slightly dislodged after the car accident possibly?). I still welcome anyone else to post any ideas they have.

Thank you for your assistance!

 

Values would have been learned since it's been a year so clearing the settings might not fix this but it won't hurt to give it a shot.

Since you changed only one sensor that might be the problem, enough of a difference in values being read from the new sensor and the other older sensor that wasn't swapped out could be causing codes to be stored in memory and the occasional cel.

 

Any luck ,I have same code but I'm a 06 sedan fi. I know this thread is old

 

On the V36 models with this code do not replace the sensor before checking the bung on the converter. The bracket that bolts to each cat. converter and also bolts to bottom of bell housing. Where the bracket attached to the converter there is normally a small hairline crack in the weld that allows cool air to enter cat.and causes the sensor to read incorrectly. Simple fix just have an exhaust shop weld the crack up for you and clear the code afterwards.