Your 2004 Mercedes-Benz may use the following procedure to reset the service reminder light.
1. Turn key to position two.
2. Press/release the “R” button to show the next service due light. Release button.
3. Turn key to off.
4. Press and hold the same R button to view the service light, then, within two seconds, turn key to position two.
5. Wait up to 10 seconds, and the light will reset to show the new service interval.