Check Engine Light On but no codes

Hello All,
I have a 2005 Grand Caravan. The check engine light came on yesterday took it to a mechanic, but no codes detected. Any idea what this could be and if I should be concerned?

Thanks
Dion:screwy:

Did he have a real scan tool that can recover more than generic codes or was he using a generic code reader? There are lots of codes out there that the generic code readers cannot retrieve.