My shop can't associate the check engine light with any codes on the diagnostic machine.
Any ideas?

Had it in shop and mechanic couldn't get a code from the diagnostics computer.. He shut off CEL but it came back on after about a mile or so of driving. Any ideas?

Likely a bad ECM. Look into getting a remanufactured ECM, with the same Toyota part number, after removing the old one.

Most likely a P0420 in the cat.

What does the scan tool data show for the downstream O2 sensors?
If data is within normal parameters, you may need a replacement PCM. Please, let me know if you do.

What does the scan tool data show for the downstream O2 sensors?
If data is within normal parameters, you may need a replacement PCM. Please, let me know if you do.

I have to get this info from the shop... don't have my paperwork with me.
Very good response... something to consider if readings are in acceptable limits