It's just a reminder to change the oil and perform any other scheduled maintenance. It's keyed to the odometer to warn you at 5,000 mile intervals. Each time you start the engine, it will illuminate for about two minutes, then the light will turn off until the next time you start the engine. It will keep doing this until you reset it. To reset it, pull the little rubber plug out of the front of the speedometer and push the button in with a tin screwdriver, then replace the rubber plug. You won't see the light again for another 5,000 miles.