99 Mystique O2 Sensors (again)

My check engine light is on, and the codes appear to say the 02 sensors are burned out (among possibly other things), and that seems to be a reliable assumption given what I've read in this forum so far.

I had a mechanic I trust to run the gamut of tests, and he sais they would first replace the 02 sensors to see what else might be problematic. Not wanting to pay the nice man his labor rates, I figured I would replace the sensors myself. My book says this car has 2 heated O2 sensors, but the mechanic suggested they would replace 4. Was he just mistaken or is there something I'm missing?

Thanks!
Brent

hes right. 2 upstream and 2 downstream 02 sensors on each bank. Its not hard...do it yourself.

hes right. 2 upstream and 2 downstream 02 sensors on each bank. Its not hard...do it yourself.

OK, that's what I gathered from looking at parts lists.

Problem is I don't have a clue where the upstreams are. Any hints where I find them or where they are described in my manual?
Thanks.
Brent

upstream are the 02 sensors before the precats on each exhaust manifold.