See also:

Mercedes-Benz M-Class Owners Manual
...

Back button
Press briefly:  - Back  - Switches off the Voice Control System  - Hides display messages or calls up the last Trip menu function used  - Exits the telephone bo ...

General notes
If the vehicle can no longer be locked or unlocked with the SmartKey, use the mechanical key. If you use the mechanical key to unlock and open the driver's door, the anti-theft alarm system w ...