A Check Engine light is usually related to the vehicles emmission control system. A sensor may have failed, usually O2 sensors.
Their is a Peake tool that allows you to scan the vehicles OBD system for Codes which would give you a better idea of what is wrong. I agree with Manolito that paying up to $100 for someone just to tell you what is wrong isnt cool. The cost of a Peake tool is about the same, but it will allow you to do future diagnostics and repairs for cheaper. Also the resale value on them is pretty good. If you ever sell the car you can include it with the car, or if your friend have BMWs you can "rent" it to them if they need!