> Could still need a O2 sensor, but if it's too lean the O2 will not produce
> any activity... thus the fault. He needs to fix the lean/rich faults first.

Okay, but -- and believe me, I'm not arguing with you, I know you're a
VW tech and you know your stuff -- how do you fix the lean/rich faults
first? I suppose there any of a number of problems that could be the
cause, and it could take any amount of time to find them. An O2 sensor
is easily located and replaced. No need to look any further, not
time-consuming at all. As I said, it's at least logically related, so
what the hell, replace it and play the percentages. If it works, then
you're all done. If you don't have a good reason to believe the various
codes are related somehow, then no, you don't just take blind stabs in
the dark.

Someone with access to all kinds of diagnostic equipment and having all
kinds of specialized skill and experience, well, that's another matter
altogether...