'00 S80 T6 Oxygen Sensor Location
 

I am trying to determine the location of the upstream O2 sensor. I see the one after the cat, but cant find any documentation on the other one (not even in VADIS). Any help would be greatly appreciated.
Also, does anyone have any opinions on the universal sensors? At $30 each, I could replace the sensor about 7 times before it would it would equate to the cost of an OEM.
Thanks!

Also, am I correct in the assumption that they are all 4 wire?

Go OEM Volvo's hate universal sensors.
The front ones are before the cats on some of the turbo cars they are just after the turbo. Some are back a little further.

What you need is BOSCH part #17036 [try Amazon.com] - DONE - trust me. If memory serves correct, these are actually 5 wire units. Regardless, this is what you need. It IS accessible with a (crowfoot-type attachment) socket. The job is, indeed - do-able. Access is unfriendly. I would strongly advise AGAINST utilizing a 'universal' sensor - bad news re. this application (and many others). The integrity of connections is subtle enough to make universals a poor choice re. many applications (voltage drops, etc.) . BUY THIS PART & PROPERLY INSTALL IT and you'll be fine, and several hundred $ above service shop involvement.:)

Oxygen Sensor
 

Which Bosch fits the after cat sensor? I believe it is a four wire.
Thanks,
Derik

Yes - 4 wire. BOSCH 16198 (oem direct-fit). It is less pricey than that darned front one:). BOSCH also offers a 'universal' for this one (15733), which may be worth considering (roughly 1/2 $?) due to the excellent connector 'kit' it features. If a few (~$50) bucks aren't crucial - by all means, use the direct fit unit.

Did you get the upstream one tackled?

Happy tinkering!

Update
 

Just as an update:
For this year/model car, the O2 sensors are fairly simple. I didnt want to separate the exhaust (bolts extremely rusted) so I simply took off the 3 exhaust cross members, unhooked the exhaust rubber supports and supported the entire exhaust line at about a 20deg angle from the car. The O2 sensors were easy to reach with a sensor wrench.
Also, BTY, the before cat sensors on this vehicle are only a couple of inches before the cat.
Thanks all for the help!!