"Check engine" (malfunction) light in 2000 Odyssey LX

The "check engine" light (referred to as a malfunction light in the
manual) in my 2000 Odyssey LX just came on a few days ago. The car has
roughly 65k miles on it and gets its regular scheduled maintenance. I
had the 60k maintneance done a few months ago, and just had an oil
change done at the dealer a week ago.

The owners manual suggests that a loose fuel cap might be the problem,
but I've removed the cap, then put it back on tightly, and seen no
change (the car has subsequently been driven at least eight times on
15-minute trips, at driving speeds of 15-60 mph).

I do have an appointment next week with the dealer to diagnose this, but
I'm looking at $100+ just to do the diagnositics.

I'm wondering if there is a way for me (no mechanical ability, no
special tools) to diagnose the problem at home, or even if there's a way
to reset the computer/warning light.