Go to Youtube,and search for Scott Kilmer. He has a radio car show in Houston, and this thread and other related ones, are based on his video which shows him putting lacquer thinner in his tank, and claims it cleans the cat.
He actually said that is second choice. First choice he says take it off the car if you can and toss it in a bucket of water with soap (laundry) over night, but they are hard to get off.
Most people, here and on the web say it will not work, but will harm your car’s fuel system. None of them have tried it.
I did a lot of Googling, and all those who actually tried it says it works. There aren’t many of them, though.
So I want to make it perfectly clear, if you try it and it harms your car, you get to keep all the broken pieces, no charge. In other words, if you try it, you take responsibility for what happens, good or bad, we do not.
I will eventually try it if my cat shows failure again. I now have my Equus 3140 scanner with me in Mexico. It started working all by itself. If it fails, I am going to try it, and if it does $2000 damage to my car, I will pay and not whine about it, because I will then know. I am a very curious person.
Some things I gotta’ do, just because. With all the insistence here it can’t work, 100% by people who haven’t tried it, my Irish stubbornness says I gotta’ try it, no matter what, though I will prefer to try it where parts are available, heh, heh.
A reminder, though. The dreaded P0420 code can, and often is, caused by other things.
Those oxygen sensors do get lazy after while, or do just plain go bad. I found a Subaru poster on a forum today, who said on Subarus it is almost always an oxygen sensor, not the cat.
The test does not actually measure the cat. It looks at gas ratios for exhaust coming into the cat, and compares it to the exhaust after going out. If the ratio falls lower than normal, they simply set the failure code for cat efficiency, P0420.
So, of course, if either sensor goes off normal behavior, it may show P0420 with a good cat.
It is generally recommended here to have a good mechanic, if you know one, check this out, rather than just laying out hundreds of dollars for a cat, to still have the same problem.
By the way, one person, just one, said a bad PCV valve could induce contamination to cause an apparent cat failure. Not verified by me.