General notes

If you cannot lock or unlock the vehicle with the SmartKey, either the battery in the SmartKey is discharged, the SmartKey is faulty or the starter battery is discharged.

replace it if necessary. Check the battery in the SmartKey and replace it if necessary.
mechanical key. Unlock the driver's door using the mechanical key.
Lock the vehicle.
contacts checked at a qualified specialist Have the starter battery and the battery contacts checked at a qualified specialist workshop.

If the SmartKey is faulty, contact Roadside Assistance or a qualified specialist workshop.

    See also:

    Checking the coolant level
    Only check the coolant level when the vehicle is on a level surface and the engine has cooled down. ► Turn the SmartKey to position 2 in the ignition lock. On vehicles with KEYLESS-GO, ...

    Interior
    The M-Class seats five people on front buckets and a three-place split rear seat that folds to expand cargo space to 81.2 cubic feet. An optional two-place third-row seat increases passenger capac ...

    Important safety notes
    WARNING   For safety reasons, switch off the windshield wipers and remove the key from the ignition lock before changing the wiper blades (vehicles with KEYLESS-GO: make sure that the o ...