1. Turn the ignition switch to the "ON" position, but do not start the engine.
2. Press and hold the "BC" (Board Computer) button on the end of the turn signal stalk for a few seconds until you see a message asking if you want to reset the service indicator.
3. Press the "BC" button again to select "Reset."
4. The display may also ask you to confirm the reset. If so, press the "BC" button again.
5. The service light should now be reset and the mileage display will indicate the next service interval.
Additional notes:
* Depending on the age or version of your BMW 645ci's instrument cluster, the wording and button sequences may vary slightly.
* If the service light does not reset after following these steps, you may need to take your vehicle to a BMW dealership or qualified mechanic to have it reset.