I know this thread has many different posts, but hoping for different insight as I think this one is a little different.

I had the 430 code and decided to try the less expensive stuff first. I have replaced all A/F sensors (except drivers side), exhaust gaskets post cat, reset all computers including battery. The MPG's shot up and running between 23-25 on HWY. There was a heavier exhaust smell prior to work, but is significantly better.

After all this work, I am now getting the 420/430 codes about every 40ish miles or so, or sometimes right at start up. Plugs look good, can't really find any air/vacuum leaks.

If this were the cat's wouldn't the MPG's go way down? The MPG's were just based off of display screen, not manually calculated.

Any need for seafood or replace spark plugs and tubes at this point? I've had the vehicle for 3 years and have put about 50K. Not really sure when the PO changed them last but they look ok. There is some brown discolor on the white shaft proximal to the threads.

Any help is appreciated as we are about to upgrade this vehicle and want to be honest selling to whoever picks this up.

Thanks!

2006 SR5 V6 T4R

Sharing my story on this issue. I am at 300K + on my 2008 V6. Just got the 420/430 Codes after running her out of gas (apparently this was coincidental as my mechanic says that the cats are not burned by leaning out when you run out of gas) and after using the TechStream to see upon testing that the reserve capacity of the cats was nearly non-existant (so they still full flow, thus no MPG deterioration), I figured I would give replacing the cats a try. I also am not burning oil, so my mechanic buddy just says they wore out. For months I have just been clearing the codes each trip and driving, and since my cats are not clogged/melted, but wearing out, it's not a problem, just a PITA.

I also looked at the dismantlers to see if I could just get a factory set with 100K +/- miles on them, but even those were $400 a pair. So, I ordered a set of the aftermarket ones from ebay few months back (~$200 total for both sides plus I bought Toyota gaskets, new studs and nuts). I have been soaking the studs and nuts in PB Blaster, WD 40 penetrant, and the acetone/ATF mixture alternatively for a few months. Will let you know how it goes. I am going to replace the A/F and O2 sensors as well (Denso units from amazon), so I am just gambling that I can get a couple hundred thousand more miles out of it.

I mean, it's only like 12 nuts for the manifolds/cats and then 10 more to unhook them from the engine and back-end exhaust..... that is 2 fewer fasteners than a 4 tire rotation, right?

Will update how it goes...