Toyota Repair: mil, indicator lamp, gas cap

Question
I have a 2000 rav 4.Last week the malfunction indicator lamp came on.I tightened the gas cap and the light went out.Easy enough.The light came on again yesterday.Tightening the cap didn't solve the problem.The light is constant.What do you suggest.Might this be costly?
Thank you very much.
                               phyllis  

Answer
Try disconnecting the battery, either the positive or negative side, wait ten seconds and reconnect it, open the fuse cover under the hood and remove the EFI fuse, wait ten seconds and put it back, if the light persists there is a problem and I advise that you have the dealer or another qualified shop retreive the troouble code(s) stored in the computer and get back to me if you need more information.
If there is an Autozone Parts store near you go there, they will let you use their diagnostic tool at no charge and help you hook it up.