O2 sensor questions?

[Kekec944/84]

Is there any way to test an O2 sensor?
How often should they be changed?
How do you know when to change them?
When they fail, how do they fail, do they read lean, rich, inaccurate or do they just fail completely?

Thanks for the help guys.

[bryanthompson]

Take a look here: http://clarks-garage.com/shop-manual/fuel-18.htm

Mine failed and my car would stumble at idle.

[nize]

http://www.the944.com/oxygen.htm

updated.

had a tough time tracking this post down, with a link to the correct oxygen sensor connectors aka: posi-lock;
http://www.posi-lock.com/lock5.html