P0420 Code Info

[2az-fedriver]

Whats up guys. heres the deal... i have an 02 camry se 2az-fe 5-speed. i was on my way to work one day and the check engine light popped up to brighten my day just alittle more. i had the codes checked and came up with P0420 Catylist efficiency below threshold bank 1. my question is could this be the downstrem o2 sensor instead of teh cat. the reason i ask this is because my car has 120xxx miles on it and hasn't used a drop of oil since i got it, the comuter hasn't thrown any misfire codes so i am pretty sure that the cat. didn't load up on raw gas and crap out. but i did have a very bad flex pipe and when the light came on it was about 20 degrees out and i'm wondering if maybe cold air got to the downstream o2 and cracked the ceramic. i would much rather replace an o2 instead of a cat/manifold assembly but i have always been a fan of if it ain't broke don't fix it so i would like a little clarification on this subject rather than just throwing parts at it and hoping i get lucky. any help would be very appreciated. because i am at the end of my wits. my car is running like ass and it didn't start until this light came on. not to mention the 100 miles a tank i lost in gas mileage when the light came on too.

[jamesqjr]

you can try getting your dealer to try to reflash the ecm with the newest recalibration. there is a TSB on this problem. the tsb # is EG024-04. sometimes i have gotten lucky and just the recalibration took care of the problem. sometimes it takes both the reflash and the converter.