Looks like my P0420 problem was.....

[Murdoc]

Quick history......
Bought a 2003 base vibe with 39,000
99,400 CEL showing P0420 replaced cat

147,000 CEL showing P0420

152,000 finally decided to replaced cat again guy who did it said cat showed some white residue but was not clogged.

189,000 CEL P0420 shows its ugly colors again this time I research and read and decide to change the rear O2 sensor clear the computer and have driven the car just over 100 miles with no CEL returning yet. Why didn't anyone who read it work on it not say anything about the O2 sensor they read a code automatically think it's the cat, I'm thinkin I probably didn't need a 2nd cat replacement. Anyway here is the Rear O2 sensor after 189,000 miles.

[ImUrOBGYN]

I don't want to be the rainy day parade, but don't count your chickens just yet. Just as an example, you went far more than a 100mi between CELs before and it may take more than a 100, now. It's been a few tanks at least since my last 420 CEL and I haven't changed a thing. I do wish you good luck.

PS - Did you test your old O2 sensor?

[circuitsmith]

Some aftermarket cats are not so durable.
It's a good idea to replace the sensors whenever the cat is replaced.
I would have recommended that back at 99,400.

[Murdoc]

I did NOT test it but it looked almost charred inside.