Georgiegirl

I'm a relatively new Subaru Outback owner (2002) and the Engine Check light has just appeared on the panel. The manual says if it's a steady (not blinking) light that stays on, the emission controls system has malfunctioned in some way. The guy who just changed my oil says he just needs to reset(?) it for the light to go away. And, I've already tightened the gas fuel cap in an attempt to get rid of the light. This car has less than 30K original miles on it. Can anyone out there expound on what could be the problem? Thanks for any help..........Georgiegirl.