Code- P0420

I'm hoping someone can help me. I've searched this forum and found different answers for this code. I took my moms car to get checked out at Autozone and it came up with code p0420. I'm trying to find out which sensor I should replace for her. I don't know where Bank 1 is. I'm going to hope it's an O2 sensor but which one? Before or after the cat converter?

Another problem I noticed while driving it there, when I accelerate from a stop, there's a bad shudder/vibration for about 1 second and then it drives fine. It almost feels like a bad clutch on a manual trans but her car is an automatic. Any suggestions?

Sounds like you may need a new cat. converter. You can try and change the o2 sensor after the converter but i think you will find that the code reappears.

If I remember right bank 1 is the O2 sensor in the header. Change your tranny fluid?

dude i had those problems. bank 1 apparently is the one after the cat. from what i've heard. i ended up replacing the cat. then a 1457 code popped up. so i replaced the charcoal canister. i would start with the oxygen sensor, since that's what i did. umm...oxygensensors.com i found really good priced ones. but then again im a newbie so you might have more experience with where to find even cheaper ones. good luck! i had a hell of a ride with mine to finally get it to riding good