Some of you may know I just picked up my maxima a little less than a month ago. I average less than 200 miles to a tank. I heard somewhere that the O2 sensor can affect your mileage. I checked the codes and there was nothing, so I left it alone. Saturday, I drove down to Chicago from my place (about 140 miles round trip). The car ran fine and I didnt' have any problems at all, but on the way back, I got a CEL. You'd never guess what the code is... O2 sensor.

Questions:

How do I know which one it is?
Should I just replace all of them now? There are 3 correct?
Where are they located?
What tools do I need? I know I can do it myself.
Where is the absolute CHEAPEST place to get them?
Anything I should look out for when I do this?

Thanks!

Sorry, I forgot to add I scanned the ECU with a code reader - and got P0130, O2 sensor circuit malfunction (Bank 1 Sensor 1)

I was averaging about 29mpg before, but now it's down to 23 mpg (highway). Seems to me that I need to wait for the CEL due to 02 sensor.

Argghh...

How do I know which one it is?
The code is different for each bank of cylinders (left-front and right-back).

Should I just replace all of them now? There are 3 correct?
There are three, I guess you could change all three....but you might want to narrow it down to two (both bank of cylinders) only IMO.

Where are they located?
Look down at your Y-pipe, you will see them attached to the pipe. Well, they were screwed in.

What tools do I need? I know I can do it myself.
You could do it yourself, and you need an open wrench or those special 02 socket to unscrew-and-screw the sensors.

Where is the absolute CHEAPEST place to get them?
Hmm...I know JRNissanparts is the best place to get an online discount from Nissan dealer (promotion code: MAXIMA), but other members could probably tell you something else.

Anything I should look out for when I do this?
....other than screwing/unscrewing while jacking up the car.....I guess it's just be careful when you are working there.

Oh! Wait for the car to cool down, will ya! Leave it off overnight. Another thing, get those non-seize paste to put in on the 02 sensor threads...this will save you the next time you are doing this. Torque for the 02 sensor is unknown for me..just tighten it up good.

If your car has a lot of miles just put in new sensors.
Might be fuel injectors as well so check that.

I'm at 63K right now. Is that considered high for a 97?

Yeah I'm in the same situtation. My CEL hasn't come on yet, and I am getting horrible gas mileage. I put a half a tank in my Max(Friday), now it's down to empty, and I haven't driven a whole lot either.

Well, that's less than half of what's on my 98...heck no...