Re: O2 sensor fault code masking another problem?
There are a few things that can "kill" an O2 sensor.
Electrical problems that cause the sensor to short out, exposure to lead, if your car is burning oil (high oil consumption) it can contaminate the sensor causing it to fail, if your car is running rich over a period of time it can deminish or destroy the sensor, also antifreeze or oil on the outside of the sensor can harm it.
Is this an upstream (before the converter) or a down stream sensor (after the converter) that keeps failing? If it is a downstream sensor, then the code you are getting maybe because of a bad converter. The sensor is after the airflow from the converter, so if the converter threshold is bad, you could get a code from the sensor because it is reading what is coming out of the converter.
Another problem could be and intermittent sensor ground.
A friend of mine went through 4 sensors before they found out that the voltage going into the sensor is not stable. In this case the voltage comming from the sensor will be too low at times and the check engine light will come on.
Hope this helps a bit, Eric.