Oil Contamination - P0420 Cat Replacement?

If you were getting oil passing through the cat it's quite possible but it could also burn off over time although I personally have never seen it happen. You should probably start by verifying the new O2 sensors are reading correctly and if money is no issue replace the cat as planned. You will have ruled out the obvious at that point. I'm in a similar situation BTW but I'm going to try foulers on the O2 rear sensor first.

SM-G935P ?

 

Spend $80 for a Magnaflow and be done with it

 

It's possible to clean the converter as I just did the same thing for my 2004 Prius with 160k miles on it (it was burning rich due to an exhaust leak). The process involves cooking your cat submerged in dilute (0.1Molar) citric acid and oxalic acid (wood bleach) solution at approximately 150 degrees for 5-6 hours. This process was taken from a 2005 study in Spain to rejuvenate old diesel catalytic converters. I did this using a stainless steel 20qt stock pot over a camp stove. I then rinsed out the cat with a garden hose, dried it out and put it back on the car. I reset the codes and the light has not come back in several hundred miles. It should help you at least pass state inspection, if that is your goal.

The jury is still out on how long this cleaning will actually last. It couldn't hurt to try for less than $20 of chemicals (wood bleach/oxalic acid $9, citric acid $6 and 4 gallons of distilled water).

Savogran 10501 Wood Bleach, 12 oz

http://www.walmart.com/ip/JARDEN-HOME-BRANDS-1440055000-7-5OZ-Citric-Acid/20469602

The concentration works out to be 76g of citric acid powder and 50g of oxalic acid powder per gallon of distilled water. Wear gloves and neutralize the acid with baking soda afterwards.

I hope this helps clean out your cat. Let me know if it works.

 

Here is link to the study I based my cleaning method from in case anyone is interested:

Regeneration of Aged Commercial Three-Way Catalytic Converters (PDF Download Available)

A couple of things I forgot to mention. I agitated this mixture every 30 mins or so by lifting and dropping the cat assembly up and down in the pot a few times. Secondly, this mixture does remove rust as well so don't be surprised if the exterior of the stainless steel cat you put into this bath comes out rust free and somewhat shiny.

 

Just to update all, as I suspected, this was not a permanent solution, but in my case, the cleaning did last approximately 3k miles before the P0420 returned. This works fine for me as I now have a spare OE cat and resonator I pulled from a parts Prius. I keep one cleaned and ready for state inspections and just swap out the clean one as needed to pass state inspections. While the failing cat is off, I clean that and make that the spare one ready for the next state inspection. This has worked well for me for the past few years.