Warning light on Dashboard on 1999 Toyota Corolla

My warning light on the top right hand side of the dashboard has come on. I checked my manual and it says that either my gas tank is empty (it isn't) or my cap is loose (it isn't) or there could be a transmission problem. I only have 40K miles on the car and have it serviced regularly. What could the problem be???

Asked by for the 1999 Toyota Corolla
Is this your check engine light? it sounds like it:

This article will give you the basics on what could be wrong and what to do next.
I'm really glad to hear that you found a fix that wasn't too painful!!

Thanks for the were exactly right. I took my car in and it's the charcoal cannister (emissions)...I also found out that there is a design flaw in the corolla with this particular part. Thanks for your help.
Well, it still is an "ouch"...the total cost will be $441 to repair. The part alone is $350...I am trying to see if I can purchase the Toyota part outside of Nevada. The dealership here is a rip off. But, I am thankful that the problem was found and your information helped to find it thanks for that.