Toyota Repair: 05 Rav 4 Check Engine Light, traction control system, 2005 rav 4

Question
I have a 2005 Rav 4 Automatic with a check engine light on and off for the past 6 months. There is no degradation in engine performance, fuel efficiency, etc. Trouble code is P0420. I have been told that an O2 sensor is bad, but not which one. I have also been told to replace the cat at a cost of $1000. Needless to say, I have not done anything since it is not running bad. The irritant is that it turns off the traction control system when it comes on. Any idea what the problem is? If it is the O2 sensor which one is it, the one just off the engine block or the one just before the cat in the exhaust pipe?
Thanks in advance for your time and expertise.

Answer
This code is specific to the catalityc converter "catalist system performance below threshold" basically it means that the cat is not working efficiently and should be replaced, O2 sensor codes are different. The factory warranty period for this is 8yrs/80,000 miles so check with the toyota dealer it may still be covered.