charcoal filter: check engine light?

[93SHO]

Thanks for the advice. i just talked with my dad again and it turned out it was the O2 sensors. however, after he had them replaced and smogged the car the CEL came on again for a couple weeks but then it just shut off and has been off since (for about a week now). could this be the computer adjusting, i know the prosches have super hi-tech computers, or is the CEL likely to come on again. the mechanic was not able to get any codes when the light was on...weird, i know.

the car is a 2001 5spd boxster with 55k.

thanks Nick-NY for the info on the charcoal canister. that must have been what my dad was talking about, not the charcoal filter!