Service Indicator Light.

Stop by your local auto parts store, most will read the codes for you at no charge. if the code that is displayed you have replaced, then just let them know and they will reset your service light.

There are usually two different lights one is the service light and the other is the check engine light. The check engine light is the one that holds the codes, not the service light. Witch one is lit and does it go out after you drive for a while?