Ahh the dreaded PO420 code, after months of clearing the code myself and researching then losing interest im now determined to fix this as cheaply as possible. Things that i have learnt about this code and people that have tried everything are: replacing the cat is a waist of time, replacing sensors is a waist of time, installing an extender spacer is a waist of time.
The only proper fix that i have found with no negative feed back is to upgrade the ECM software (PAC FILE UPDATE FOR CATALYTIC SYSTEM) in your car which for some reason was never offered in Australia but in every other country nor have local Subaru dealers heard about this update. Now my mechanic does have this software that he had to purchase from Germany for $250, and is willing to install it for $275.
The question is: has anyone seen this software online for free or cheeper? please help its such a pain in the arse to have to clear the codes every 2 weeks and then have the idle reset only to have me hopping along the streets trying not to stall the engine!