O2 sensor in Mazda Protege

My 2003 MazdaSpeed Protege with 79k on it is getting an intermittent CEL with code P0171 (Too lean - bank one). I believe it is the O2 sensor. I have already cleaned the air intake and MAF. My car has two O2 sensors and the front one, the one that is typically the culprit, costs $240 just for the part.


Is this likely to be an extended warranty covered item?

If so, should I take it to the dealership I bought it from or the one I usually take it to for service?

If not, is this something I could feasibly fix myself to save labor costs? (I do have some mechanical know-how, but these newer rice burners are kind of new to me; I’m more experienced with good ole Chevy’s)

Where exactly is the sensor located?

Any other related information would be awesome as well.

Thanks for the help folks, and happy driving.


If you have an extended warranty then the sensor may be covered. It depends on the warranty and what it says it will cover.

I tend to think the sensor isn’t bad but it may be. There could be a intake or exhaust leak causing this problem. A shop should be able to determine that. The sensor may be near the input to the CAT.

Really?!?! I was told that my car sounded like it had an exhaust leak when I had an alignment done a few weeks ago. That’s probably a cheaper fix than the O2 sensor. I’ll look into that. What’s a good way to tell if I do have an exhaust leak? It does sound like I have a rattle at start up coming from just behind the motor. Also, I have a fuel ratio gauge in my car which has been showing it running a little lean at idle but not during driving. My car has a turbo and there is a little oil on the underside of the turbo body. Is this normal for a turbo or could that have something to do with an exhaust leak?

The O2 sensors will look like spark plugs screwed in tot he exhaust somewhere. Teh upstream one is usually close to the exhaust manifold. The downstream one, closer to or on the CAT. You have to feel about for them at times.

If you are good with a soldering iron, you might get a generic one with no plug on line, then transfer the wires and there you have it.
Obtain the part number off the old one and search online for replacements.


A leak would upset the readings. If you feel along the exhaust while the car is running, you may feel a jet of exhaust and/or a hissing sound where the leak is, usually at a joint.

oil on the Turbo is not good, but shoud not cause any AFR imbalance, unless you are leaking a lot of oil into the exhaust or intake. So how is your oil consumption.

I typically have to add about half a quart between oil changes. I do oil changes at about 4k, and I switched to synthetic blend last time I changed it.

If there is an exhaust leak between the head and the O2 sensor it will cause the sensor to generate the trouble code. I don’t recommend changing anything until the problem is pinned down using proper trouble shooting procedures.

Ditto to all of the above XLNT info.

Looks like it’s time to find out if that extended warranty is worth the paper it’s printed on. Does it cover exhaust leaks?

FWIW heres some other possible causes for your lean code: vacuum leak, faulty injector, low fuel pressure, faulty MAF sensor.

BTW, congrats on not “shooting the messenger.” Lots of perfectly good O2’s get replaced & at OUCH $240 bucks apiece this gets expensive. Lean or rich codes are not a good reason to replace the O2.

Thanks for the replies. You guys rock. Any other info would be great. I’m a knowledge hound and I always have questions.