Join Date: May 2007
Car: 2003 2.5 4EAT with AWP.
Feedback Score: 0 reviews
I think your mechanic is wrong and whaty he told you is exactly the opposite of reality with our cars (I'm assuming you have an Outback. Year? Miles?)
P0420 is VERY RARELY a failing cat.
It is most commonly a failing oxygen sensor (front Subaru, rear any brand), vacuum leak, exhaust leak or what not.
Search that code on the forums and you'll find plenty of info.
Cats rarely fail without serious mechanical problems, I think your mechanic wants to give you an expensive repair bill.
2003 Outback wagon: "Kaylee". 153,000 and counting.
Basics: Quaker State conventional 5W30, Motorcraft oil filter, Fram air filter, Valvoline Maxlife Dex/Merc ATF, Mobil 1 75W90, Michelin Primacy MXV4.
Mods: Scangauge II, 2004 Forester XT shift knob, Fumoto oil drain valve, Phillips VisionPlus H1 low beams, Phillips 9011 HIR1 high beam upgrade, Nokya Hyper Yellow 2500K fog lights.
Also: More rust than I care to think about.