I have a P0420...

Basically it's saying my driver's side cat is PMSing...can I get an O2 simm and pass CA smog that way? Or do I have to replace it?!?! Thanks guys...

The O2 simulator will tell the ECM that the sensor is funtioning,it won't change the emissions. Time to get a new cat.

That's the thing though...it doesn't seem bad. It all smells fine, doesnt smoke. Pretty soon I'm going to be getting LT's and ORY so I don't really wanna buy a cat for a couple hundred miles...

Swap O2's over and see if the code follows. If it does then it the O2 sensor and not the cat.