Error code P0420

[jezcar]

Hi all

I have been driving the car to and from work each day and about 4-5 months ago the orange engine light came on, but due to the hours i work was unable to get to a garage or reader to find out what was wrong before the light went out. This happened a second time about 6 weeks ago, just after it went out I had a mate check for stored faults, guess what no stored faults.
The last time it happened, a few days ago I went to my mates on way home from work while light still on and he plugged his computer in and it came up with the following error code -

'P0420 - Catalyst effect below threshold (bank 1)'

My friend reset the system and when i started the car the light didn't come back on and has remained off since (about a week).
From the fault I am assuming the fault could be one of three things:-

1) The pre Cat lambda sensor
2) The Cat itself, or
3) The post Cat lambda sensor

I have done some research and what I have found suggests that the post Cat sensor could be at fault, if anyone has any definitive answer I would be much appreciated as I don't wanna spend out even more on parts that I have to spent more than enough since Christmas as it is!

Cheers
Jez
:shrug:

[Simon.h]

Hi, the pre cat 02 sensor just does the fuel trims and post cat sensor checks the cat.
1st thing to try is to swap the 02 sensors over (only if they are the same, the V6s are) and see if the same fault code comes back.

[jezcar]

Hi Simon

Thanks for that will swap them over asap if i can and as soon as the light comes back on will get to my mates computer and read any fault that is given and come back then.

Jez