failed inspection code 0420 . bank 1

[2004boxterS]

I changed o2 sensors...failed again. [.10/18/2018 deadline for inspection]  what should I try next?

[Ahsai]

P0420 is the bank1 catalytic converter efficiency too low and has nothing to do with the O2 sensors, which have their own codes.

 

You can use an OBDII scanner to monitor the signals of the O2 sensors on bank 1 to confirm the cat is indeed bad (when the post cat signal follows the swinging precat signal, the cat is bad). The only fix is to replace the cat.

Edited October 15, 2018 by Ahsai

[Ahsai]

You may want to try ebay for a used one. It's rolling the dice without an easy way to verify if it works before you put it on your car. I usually look for ones that were taken off lower mileage wrecked cars.

 

You can search for "2004 boxster downpipe" on ebay.

[2004boxterS]

thank you Ahsai , 

also I get a   P0430 code

[Ahsai]

You're welcome. It's likely you have the same problem on the other bank then.

You may also want to check out this thread for more info