Check engine soon light

Can anyone tell me what might be causing the check engine soon light to come on? IT came on over the weekend, we checked everything, drove abour 350 miles and it went off. Then came on again last night. We checked to make sure the gas cap was on tight, that was a problem I had with another car.
Any advice is appreciated!!!!

Take it to AutoZone. They can scan it and tell you the code and what it means...Free!

well that sounds wonderful!! thanks

They can scan it and tell you the code and what it means...Free!

Then once you get the code,let use know what it is and we will help you figure it out.

~Larry~

http://img.photobucket.com/albums/v285/BIG-L/DalesDaytona.jpg

With my car, the service engine light is on too, I live in MD; do all the auto zones check it for free? Also, my transmission was slipping, could that be the cause of the service engine soon light coming on, I really do not know?