330ci Service Engine Light Always On

I have a 2001 330ci with 25,000 miles. My computer says I have another 6,000 miles before my next inspection. However my service engine soon light comes on for a couple days, off for a day, now its been back on for about a week. A BMW tech said it could be because of my gas tank cap is not closed tightly enough. I tighten it every morning and the light is still on...anyone with similiar experiences or suggestions?