It sounds like your problem's fixed, but I wanted to post the 'testing 02 procedure' for you and anybody else searching this post.

First Test
1) Disconnect the 02, but leave the battery connected
2) Measure the resistence between the PWR and GRND terminals of the sensor. it should be approx 6 ohms at 68 degrees F.
Second Test
1) With the sensor connected and the engine running, measure the voltage between the H02S and SIG RTN (Ground) of the 02 sensor. voltage should fluctuate between 0.01-1.1 volts.
If the first test doesn't read around 6 ohms, or if the second test yeilds slow fluctuation or voltage isn't within specification, replace the sensor.
I hope you don't have to replace your sensor , but if the cel comes back on, try out these tests and let us know the results.