hi guys.. its me again i thought i had this done today but i guess my car really really hates me. Okay so i am throwing a p0420. When i went to go get inspected today before the CEL came on all systems were good and the catylist was ok aswell. evap system was N/a and secondary air injection system was n/a... so they could not do inspection... meanwhile i get home about 100 miles later and as i pull into my driveway, vwalla, p0420 code throws again.... i have replaced everything that i think will throw this code, does anyone have any idea what's next to try...?

Here is a list on replaced stuff.

New front o2 sensor, new rear o2 sensor, brand new CAT, Brand new gaskets, Brand new hardware....

What else can this possibly be ... it just wont go away. its like a bad nightmare. thanks for the help..

 

That can only be caused by a failing cat or failing O2 sensor (front or rear). Those are the only options.

Are you SURE that those 3 items are actually new?