Hi all,

Initially, I got P0300, then I got a bliking CEL but had to drive, then changed the spark plugs and the CEL went away. But after a few miles at ca 50mph, I got a new CEL. I got it checked today and got the dreaded P0421. It might be that the catalytic converter (WU-TWC) got ruined.
I know it could be the oxygen sensor after the cat or before, and I will check them before attempting to change the cat. Or that there is a trick to fool the rear sensor, I just read that.

So, I have a few questions:

1. If I just ignore the problem, meaning do nothing, is the car safe to drive, would I have any issues? So, we, the humans will we have any problems? Second, would it cause more problems to the car meaning more/higher repairs in the future?

2. Can replacing this cat be done by a home mechanic (me) in the parking lot? I am not that experienced but have done a few things.
If so, here are more q:
- which cat to get (wagner=$300, bosal=$200, etc)? did you get it from the internet of your local AA or Napa?
- can anybody point me to a site with instructions?
- what about the gaskets above and below? could this lead to leaks?

Thanks. Neko