[V6-12v] Check Engine Light

[Nathan Widmyer]

For a couple weeks I've been getting the check engine light
intermittently with no real common thread of occurance.  I can go to
or from school and home (about 100 miles) with no light and the next
day go to the 7-11 (3 miles) and get the light, or vice versa.  The
light also turns off before the car is turned off too sometimes, not
always.  For example, I can start the car and 5 minutes later, the
light comes on and 10 minutes later it turns off.  The engine doesn't
seem to change performance characteristics if the light is on.

I checked the trouble codes from the climate control and I get "00o"
meaning no trouble has been found.  What can I do, being at school
with no tools, at least find out what can be the problem?