vectorpro

Hello, I am troubleshooting a P0420 code on my 2002 9-5 ARC wagon. The car has 130,000 miles. The code appears intermittently but with sufficient frequency to not allow me to get the car through our state emissions test. I have cleared the code with a scan tool device, but was told at the test facility that the car needed to go through several "Drive Cycles" in order to be able to be tested. Does anyone know any specifics of what would properly reset the ODB system to a status that would allow it to be tested. Also, does anyone have any insight based on the history of these vehicles what the likelihood of a bad CAT or faulty O2 sensor. Obviously the O2 sensor would be cheaper to replace than the CAT, but maybe someone has had a similar experience with this car and can give me some advice.

Thanks
Jim