I just did the front one over the weekend, and it took me ~45 minutes. I even did it with the car on Rhino Ramps.

You'll need either a 22mm or 7/8 open-end wrench. The 7/8 isn't a perfect fit, but it's close enough. Try getting under and loosening it first (follows standard threading principles of righty-tighty). If it's hard to loosen, start the car and let it idle while you go inside and dig out an old flannel shirt. The flannel shirt will protect your arms from warm undercar parts, and the warm exhaust will hopefully have expanded enough so that you can loosen it without using beat-up tools.

The most difficult thing I encountered was getting my not-so-large hands up to the connector. It's roughly over the left-hand steering linkage bellows. I've actually got to run right now, but if you want details on how I succeeded, then drop me a line.

-cj

cliff....hold the phone !!!!
did you check all your vacuum lines? it is very rare for both o2 sensors to go bad, esp. the rear one. check bay13 to locate the vacuum hoses (usually the elbows) that tend to wear out. your front o2 sensor might need changing but your rear, too???? the sensor is fairly easy to remove and install. it is the wiring connector that is a bixxx to do. before all else, give the o2sensor a good dose of liquid wrench or similar product to make removal a little easier.
good luck

how much did you pay for the 02 sensors. the dealer here in Charlotte wanted 192 each and i need both. they are pretty easy to intall, takes about an hour for both of them. i have already take them off before to inspect.

Chad
--
94 854 turbo. (272 whp in 2nd gear @ 16psi)

This site has step-by-step instructions that might help:

http://volvospeed.com/Repair/o2sensor1.htm

Cliff, I have 2 '96's 135k &147k both which failed the Nox emissions TODAY. A volvo serice manager said most likely the CAT. one had an EGR valve done about two years ago. Please keep me informed if the O2 sensor work as the are less money than the Cat.
Thanks,
Jot