Thought this might help someone. I have read threads on different sites that O2 sensors are a bear to remove. Well, my "check engine" light went on yesterday. I went to Autozone and got a code of "P0420". This had the message, "...the catalyst system efficiency for bank 1 is below threshhold for the current engine operating condition..."

I picked up a Bosch O2 sensor and one of the O2 sockets (slotted). It was not that hard to remove. I ran the engine fo a minute, sprayed some penetrant on the sensor, waited five minutes, sprayed it again, then waited five more minutes. After a few taps to the ratchet handle by with a hammer, it loosened. The Bosch came pre-gooped with the (specialized?) anti-sieze paste already on the threads.