Is it possible to test individual O2 sensors?

[EdgeCat]

I keep getting an intermittent CEL, and after having had it checked a few times, I know it's the o2 sensor(s). Problem is, AutoZone can't really tell me which one it is, and to complicate things, I have MILs on the lower 2. Is there any good way to check to see which one(s) are bad, so I don't spend an extra $50-100 on sensors I don't need?

(Wasn't sure if this fit in problems or not, since it was more of a generic question.)

[FastCougar]

yes, quite easily (http://www.gracieland.org/cars/techtalk/O2_1.html)

[EdgeCat]

:bowdown:

You rule, Trevor. Looks like this is my problem, as I'm experiencing a LOT of the symptoms of a dead/dying O2.

[FastCougar]

When it comes to things like this, I would rather just get them all in one pass and rest assured that I don't have to repeat the job later down the line because the other one goes out. Just replace both upper O2's at the same time ... cost will double, but future work will be cut in half and you only get dirty once ... it's a trade-off :shrug:

[EdgeCat]

There are 2 uppers and a lower, correct? The one variable I'm not sure about are the MIL eliminators in the uppers since I gutted the precats.

[FastCougar]

MIL-Elims are supposed to go on the lower O2's and since that value is being fooled anyway by the eliminators, I wouldn't bother replacing them. Replace the upper 2 ... those are the once calculating your A/F ratio. The lower O2's are only there as a reference to the top to determine catalytic functionality.

This setup I describe is for the 99-00 ... 2001+ have 3 O2's ... 2 upper for A/F and one lower after the main cat to determine effecienty.

[EdgeCat]

So as long as the MIL eliminators are functioning properly, I won't ever really need to worry about replacing the downstream O2s (since they don't really work anyway)? Any idea how difficult replacing the two upstream sensors tends to be?

[Pinhy]

This belongs in Problems since it is Cougar related.