Update:
Had the 4runner at the dealer. The service rep says that the 2nd bank (not the one that was replaced in January) has "failed". I peppered the rep with questions about what diagnostic tests they ran, etc. and she put me in touch with the service manager.
I asked the manager what are...
So back in January of this year I got the dreaded P0420 code on my 2004 4Runner (126k miles). Took it to autozone was told the usual. Took it to the dealer. They checked for sensor problem and determined one of the converters needed replacing. Cost was right at $1k.
Fast forward 10 months...
