oxygen sensor woes

[5269]

I recently purchased a 2006 Nissan Altima 2.5. Shortly after the SES light comes on with code P2A00. Replace upstream sensor with AC Delco o2 sensor and erase code. 50 miles later same code comes back.

Anybody have any input on what I did wrong, or what parts I should look at next? Car seems to still run fine but I can tell the mpg is not where it should be.

Is it possible I got a new defective sensor or is there something else going on?

Any input would be appreciated.

[Macgyver55]

Could be a bad catalytic converter, or an exhaust leak. Sensors can be defective and some cars are a bit finicky about aftermarket ones but, without seeing data its only a guess.

[aanderud]

Is there a chance you have more than 1 sensor, and you replaced the wrong one?

I have 2 of the 02 sensors on my dodge, and there are plenty of vehicles which have 4 of them (one on each side of each oof 2 catalytic converters). Anyway, I got a code and replaced the rear sensor on my dodge ram a few weeks ago. This was a few hundred miles ago and so far so good. However, considering the first sensor went bad at 96k miles, and others online say they often get 100k or so out of these sensors, I'm expecting the other sensor to go bad soon.

And as macgyver55 mentioned, some vehicles don't like aftermarket 02 sensors at all. I paid a bit more for original equipment part on my dodge but figured it was worth not having hassle later, as the difference was only something like 20 bucks.

[Scott K]

Code P2a00 can be a lot of different things. Without proper diagnostic tools on this one, you could be throwing parts at it for awhile. As for your aftermarket o2 sensor, on Asian, and European built vehicles, I make it a rule not to use aftermarket computer sensors. That doesnt mean it is the cause. Which bank did you replace? The one by the firewall?

It could be a vacuum leak, a bad mass airflow meter, exhaust leak, or a missfire, amongst other things. If you are determined to fix it yourself, be prepared to throw a few darts before getting it correct. Also, when you use aftermarket parts for trial and error, you never really know, if the part you put in, has eliminated the possibility of that part not being it. So after you throw a bunch of parts at it, then you need to go back and second guess that maybe, it is a bad part, or the aftermarket ones, just arent up to its specs.

[5269]

I replaced the sensor by the exhaust manifold. I'm thinking there are just 2 o2 sensors on this car.

I do notice what sounds like a small exhaust leak when starting the car cold. It is not noticeable when the car is warmed up.

Sounds like I better just take it in.

Thanks for the replies guys.