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How many O2 sensors on a 1996 Mercury Mystique/Ford Contour 2.0L Zetec, automatic transaxle

Hey guys, this is a really silly question, but I can’t for the life of me figure out how many friggin’ oxygen sensors this car has. The Haynes manual says there is one oxygen sensor, located in the exhaust pipe. However, it looks like there is a second one in the exhaust manifold. Should I trust my eyes instead of the manual? If the sensor in the exhaust manifold is not an O2 sensor, what the heck is it? I can’t find it in my manual, nor after hours of digging around on the internet.

Anyway, the reason I’m playing with these sensors is that I got a CEL about an O2 sensor, bank 1 sensor 1 (and I should have written down the code, because I’ve forgotten it now). I got a sensor from the auto parts store, and the one they gave me was an upstream sensor which does not fit on the exhaust-pipe mounted O2 sensor (plugs are rectangular on the replacement, circular on the original).

So the question boils down to, “what should I do?” but mostly I’m wondering if there are two sensors, which to replace, and with what component?

Hopefully that all makes some sense! I’ve attached pictures of the two suspected O2 sensors. The first is the one mentioned and pictured in my Haynes manual (mounted on the exhaust). The second picture is the one in the exhaust manifold, which is not mentioned by Haynes.

Thanks a bunch,


1996 model year = OBD2 = 2, one before and one after the catalytic converter.

So bank 1 sensor 1 would be the upstream sensor, correct?

And that’s what I get for trusting the manual! A bunch of confusion!

Yes, bank 1 sensor one is the upstream one in the manifold.

Also be aware that a CEL w/DTC for an O2 sensor doesn’t necessarily imply there is something wrong w/the O2 sensor.

you are very right George. Usually the cause is a vacuum leak. Deteriorated hose, PCV most likely, or leaking intake gaskets

Hmm, well I’m gonna pop off the O2 sensor to take a look anyway. I’ve done some cursory looks for leaks but I reckon I should get some carb cleaner and check for vacuum leaks. I’ve been putting off checking the PCV system because it’s underneath the intake manifold and sort of a pain to get to, but I know it needs to be checked. I figured that vacuum leaks, etc, would cause a lean code rather than an O2 sensor code but I am pretty much a novice still! Thanks for the advice guys.


Please post the exact code, NOT the interpretation

For example, P0130

Not all oxygen sensor codes can be blamed on an exhaust or intake leak. For example a oxygen sensor heater code.

Yep, I forgot to write down the code, so I don’t have it for you. Apologies! I’ll get it read out again when I head to the auto shop.

No offense, but your car’s pretty old

All skepticism aside, there’s a fair chance the oxygen sensor truly needs to be replaced

No offense taken! She’s old, but she’s only got 60,000 miles on her, so I’m trying to keep her in good shape. 60,000 miles means, though, that a lot of maintenance that would have been done ten years ago hasn’t been done yet. I’m waiting for old, infrequently used, parts to start falling off and I don’t mind swapping them.