Oldsmobile/Buick Repair: Service light, batt cable, model ford

Question
My service engine soon light has come on and is a steady light, but there seems o be nothing wrong with my car. My owners manual said that if I had recently put fuel in and cap was left  loose this would cause it also, someone had put fuel in not long before the light came and I checked today and the cap was loose, will the light go out soon or does it need to be check and shutoff by a mechinic?
Thank you

Answer
hi bill.  well you didn,t say what type of car you have .if you have a late model ford or gm.then yes this could be what caused the prob.you see cars today have a purge system .every few mins it will actually pressureise the tank to make sure it is not leaking if for some  reason it will not hold the pressure then the computer assumes their may be a fuel system prob.and set,s the light.but is that the prob we don,t know is your car going to leave you stranded not likely.so bill just to try and save you a 85.00 labor bill try and disconnect your neg batt cable for 30 min or so if light stays on or comes right back on you will have to go for service if not then assume the cap was the prob.good luck bill     billymac