Evening all,i bought my 2004 STI 3 week ago with no lights on dash,ont the way home roughly 30 mile into to the journey the engine management light came on,so i borrowed my mates little cheapo code reader,it was PO420.So then removed the light.
Drove it again today and its come on again,after around 30 mile,not straight away.
P0420 means catalyst system efficiency below threshhold,It has got a sports cat in it,could it be that,the previous owner says hes never had it come on but he could be telling porkies i suppose.

Is it worth taking it to someone with proper diagnostic tools to pinpoint the problem..

Thanks

Andrew

 

certainly is

 

Thanks.is there any way to get rid of it by mapping it out or something??

 

it's more likely to be the rear o2 on the way out. Yes it can be disabled with a laptop along with the rest of the codes for the rear o2.