DOS_GRID, Thanks for the info on cleaning cats. The thing is that my cats are not clogged, so I'm not sure if water/detergent cleaning would be beneficial. Perhaps I'll look into this when it gets warmer here (summer time). For now I went with the suggestion from couple of folks on this post and a related one and installed the anti-foilers on the downstream O2 sensors. It seem to have worked as far as not tripping the code.

The Cataclean also worked for me.

Perhaps it depends what is going on inside the cat. If there is oil or some other stuff, CataClean may be able to clean it out.

Nice to know DOS, Tks. for the input bud...

I just had the P0431 code, I took out Bank 2 Rear O2 Sensor (Left), and inspected it with a magnifier, it had carbon, but no pieces or debris of the Cat. If upon inspection I had found debris for sure I had a bad Cat Converter. Changed the O2 sensor, and code P0431 dissapeared (fixed).

But, if you have to change your Cats, as nothing else fixes it, there is an inexpensive solution, which might be illegal in most States. If you are in a State where gas emissions are not checked, there is a way to eliminate the Cat Converters and not have the Service Engine Soon Light ON forever. There is an O2 Sensor Simulator Module that will fool the signal and make your ECM think that everything is fine with your Cats and/or sensors. There are other tricks of the trade, but with modern engines it is more difficult to fool the vehicle's ECM without an electronic aid like the Simulator. One of the tricks is to weld an O2 nut (thread) further back in your exhaust system as to install the rear O2 sensor there, where it will receive cleaner/cooler exhaust fumes, therefore having the ECM read less emissions and believe it is working properly.

Do you remember which detergent you used and detergent to water ratio?