The other day I was driving down the road when I noticed my CEL was on. I pulled the code and got p0420. I'm having trouble finding info on solutions since most of the threads are about lancers running an aftermarket exhaust system.

I have an 09 lancer with a PZEV flashed ECU.

Also, is their any way I can find out if its the cat or the sensor without replacing everything?

 

From in my past this code usually comes from a bad oxygen sensor or one going bad. However this thread has some interesting info on it..http://www.evoxforums.com/forums/showthread.php?t=34136

 

Hello, what's the o2 sensor for code P0420 ?? Upstream or Downstream? and where is located?

 

It is the downstream (second) O2 sensor.


It is right after the cat converter.