Fault code Cat

[clemo]

Hi,  So ive put a new 3" Sports CAT down pipe on  to stock back  and tonight after a bit of a run  management light came on , i have a maxi scan in the boot so i stopped and checked it said : P0420 Catalyst System Efficiency Below Threshold Bank 1

Any Ideas please
Thanks

[Flyingscotsman]

The ECU thinks the OEM VW cat is still there and is working below it's efficiency.  Some people find a lambda probe spacer works, but I believe the only sure way to remove light is to get lambda probe mapped out.

[clemo]

Thanks for the info .... Are we talking the probe up near the turbo or behind the CAT

Cheers

[olethalb]

behind cat, or 'post cat' monitors the efficiency / operation of the cat

[clemo]

This fault pops up every day , can i not address the issue with VCDS

[Flyingscotsman]

You need to get it mapped out or use a spacer as said above. 

[clemo]

OK thanks ill try spacers , after the CAT , now i did another Maxiscan and the volts look good on sensor 1 fluctuating between lean and rich but on 2 its also up and down, does this mean the CAT ive just got is no good ?? How can i check if the CAT is working correctly  i have VCDS