P0420 code keeps popping up

Hello all,

I bought my subi legacy 2.5i N/A non turbo limited edition about 1.5 yrs ago with 77k miles now has 90k.

And about 3-4 months after buying the car this P0420 code has been bothering me for a year now.

So about myself I have worked on cars for about 10+ years from N/A to turbo cars (Having a Talon on E85) so I know how to work on cars and this is the first car that has me stumped.

So to begin yes I have replaced both front and rear O2 sensors with OE parts. So I went to a dealer so I can have the cat replaced under the federal warranty of under 80k they have to replace it, then they told me it was damage (thinking it is a salvage title subaru). So I said ok how much to replace and asking over $1k so I said NO. Went online and purchase an aftermarket cat converter. Aftermarket (pacesetter) one because it was cheap and after about maybe 200 miles it came back up with the dumb CEL. Also I looked at my OEM and it is not damage at all no dent no nothing, inside was clean and no damage. Dealer lied and probably didnt want to fix it for free and they saw it was a salvage title also. So I figured it has be something else, I had a couple exhaust leaks fixed.

Nothing still getting a CEL. Next was a MAP/MAF cleaner, cleaned and went for about 150-200 miles and still getting the CEL (usually pops up before 100miles). Next I replaced the PCV valve with OE.

Then went back to return back to OEM cat and some Cat cleaner and got about 250 miles and almost a full tank of gas before it came up again.

Also no power loss what so ever, MPG is 28 hwy and city 22 and combined at about 24mpg.

I give up!

Any one can help me on this. Is there a reflash for this Legacy (recall?)

I am about to sell this car.

Please help. thanks

Needs a cat.

Dealers don't lie about warranty. It's free guaranteed money for them. Warranty is a "customer" the bill is just paid by subaru. I don't know where people get this thought in their head that if you have a problem it comes out of the dealers pocket. It doesn't work that way.

Pacesetter is a terrible product. Guarantee the cat wasn't efficient enough. A cat is not just a cat. They have to have a certain amount of precious metals.

If it bothers you that much to have a light on or your in an emissions area then go pick up a 19mm spark plug non fouler drill the center out and screw the sensort into it and screw all of it into the exhaust. (Just do the rear o2)

It'll fix the light. You don't need a cat it's just emissions stuff.