You can test the O2 fairly easily with a digital volt meter...find the splice to the O2 power wire (usually black) under the passenger seat carpet and disconnect the two halves. Then stick a small shunt into the female half of the connector (short piece of light guage bare wire). Then reconnect the two parts with the shunt pinched in place.

Using an alligator clip from the DVM, connect the positive clip to the shunt (red wire), and the negative clip to a ground connection (seat bolt head). Using the < 2V scale take the DVM readings after warming up the engine...take the readings at or around 2500 rpms. If the O2 is good, the values will cycle up and down across 0.5V. If they are fixed at a value above or below that, then the O2 is likely no longer functional. If you do not connect the meter in parrellel, then the reading will be fixed at around 0.42V (DVM hooked up wrong in series...don't ask me how I know)

You can also remove the O2 and bench test it if you have a propane torch and a DVM plus bench vice...Heat the bulb until it is incandescant, then read the values between the bulb (black probe) and the other half of the O2 (red probe)...Do this test heating continuously for around 3 minutes...the DVM value should never drop below 0.9V..if it drops to .89V even then your O2 is bad...Remember to continue heating the whole time of course.