Hi all,
I've got fault code PO420, catalytic system efficiency below threshold , it's had two brand new cats and all four lambda sensors done, after 100 to 150 miles the codes come back on, does not seem to affect the performance
Also I have had the backbox deleted and straight pipes to tips put in its place

Thanks in advance
Joe

 

Are they OEM cats?

 

Check fuel trims.

Examine the freeze frame data a few times for clues.

 

Good point. May have to disconnect the battery to do an ECU reset.

 

The point of that being what?

You'll unset all the OBD monitors. With a car with a known fault they may not set again until it's fixed. Should that occur you may really struggle.

 

Oem cats fitted and also will check fuel trims next time I get it out
Very annoying fault after the £££ spent to repair lol