2000 Monte Carlo MIL is on - but no codes?

Not sure where to post this...but a buddy came in with a 2000 Monte Carlo SS 3.8 that is lacking power. The check engine light was on so I hooked up my OTC scanner, no codes and none pending? Cleared the light but was wondering if anyone else ran into this?

On a side note the upstream O2 sensor is cross counting "very slow" and even sticks momentarily...but figure it might be a good to investigate the MIL situation before changing parts.

Ironically I found a post online where another 2000 Monte Carlo owner had the same MIL problem...but had no answer to his question. (pcm issues?)