Mercedes-Benz C-Class Manuals

Mercedes-Benz C-Class (W205) 2015 - 2021 Owners Manual: SmartKey

Overview of SmartKey functions

WARNING Risk of accident and injury due to children left unattended in the vehicle
If children are left unattended in the vehicle, they could:
  • Open doors, thereby endangering other persons or road users.
  • Get out of the vehicle and be hit by oncoming traffic.
  • Operate vehicle equipment and become trapped, for example.

In addition, children could also set the vehicle in motion, for example, by:

  • Releasing the parking brake.
  • Shifting the automatic transmission out of park position j or shifting manual transmission into neutral.
  • Starting the engine
  • When leaving the vehicle, always take the SmartKey with you and lock the vehicle.
  • Never leave children and animals unattended in the vehicle.
  • Keep the SmartKey out of reach of children.


NOTE Damage to the key caused by magnetic fields
  • Keep the key away from strong magnetic fields.


  1. Locks
  2. Battery check lamp
  3. Unlocks
  4. Opens/closes the trunk lid
  5. Panic alarm

The SmartKey may vary from the one shown in the diagram, depending on the vehicle equipment.

The SmartKey locks and unlocks the following components:

  • the doors
  • the trunk lid
  • the fuel filler flap

If the vehicle is not opened within approximately 40 seconds after unlocking, it locks again. Antitheft protection is activated again.

Do not keep the SmartKey together with electronic devices or metal objects. This can affect the SmartKey's functionality.

battery check lamp 2 does not light up after pressing the or button, the battery is discharged.

Replacing the SmartKey battery.

Activating/deactivating the acoustic locking verification signal

Multimedia system:

Vehicle → Vehicle Settings → Acoustic Lock

  • Activate or deactivate the function.

Activating/deactivating the panic alarm


  • The ignition is switched off

The panic alarm function is only available in certain countries.


  • To activate: press button 1 for approximately one second.

    A visual and audible alarm is triggered.

  • To deactivate: briefly press button 1 again.


  • Press the start/stop button on the cockpit (the SmartKey is inside the vehicle).

Changing the unlocking settings

Possible unlocking functions of the SmartKey:

  • Central unlocking
  • Unlocking the driver's door and fuel filler flap
  • To switch between settings: press the and buttons simultaneously for approximately six seconds until the battery check lamp flashes twice.

If the unlocking function for the driver's door and fuel filler flap has been selected:

  • Pressing the button a second time centrally unlocks the vehicle
  • Vehicles with KEYLESS-GO: If you touch the inner surface of the door handle on the driver's door, only the driver's door and fuel filler flap are unlocked.

Deactivating the SmartKey functions

If you do not use the vehicle or a SmartKey for an extended period of time, you can reduce the energy consumption of the respective SmartKey . To do so, deactivate the SmartKey functions.

  • To deactivate: press the&button on the SmartKey twice in quick succession.

    The battery check lamp of the SmartKey flashes twice briefly and lights up once.

  • To activate: press any button on the SmartKey.

When the vehicle is started with the SmartKey in the stowage compartment of the center console, the SmartKey functions are automatically activated .

Removing/inserting the emergency key


  • To remove: press release button 1.

    Emergency key 2 is pushed out slightly.

  • Pull out emergency key 2 until it engages in the intermediate position.

You can use the intermediate position of emergency key 2 to attach the SmartKey to a key ring.

  • Press release button 1 again and fully remove emergency key 2.
  • To insert: press release button 1.
  • Insert emergency key 2 to the intermediate position or fully until it engages.

Replacing the SmartKey battery

DANGER Serious damage to health caused by swallowing batteries
Batteries contain toxic and corrosive substances.

Swallowing batteries may cause serious damage to health.

There is a risk of fatal injury.

  • Keep batteries out of the reach of children.
  • If batteries are swallowed, seek medical attention immediately.


ENVIRONMENTAL NOTE Environmental damage caused by improper disposal of batteries
Batteries contain pollutants. It is illegal to dispose of them with the household rubbish.

Dispose of batteries in an environmentally responsible manner.

Take discharged batteries to a qualified specialist workshop or to a collection point for used batteries.


  • You require a CR 2032 3 V cell battery.

Mercedes-Benz recommends that you have the battery replaced at a qualified specialist workshop.

  • Remove the emergency key.


  • Press release button 2 down fully and slide cover 1 in the direction of the arrow.
  • Fold out cover 1 in the direction of the arrow and remove.
  • Remove battery compartment 3 and take out the discharged battery.
  • Insert the new battery into battery compartment 3. Observe the positive pole marking in the battery compartment and on the battery when doing this.
  • Push in battery compartment 3.
  • Re-attach cover 1 and push it until it engages.

Problems with the SmartKey

Problem Possible causes/consequences and ► Solutions
You can no longer lock or unlock the vehicle. Possible causes are:
  • The SmartKey battery is discharged or nearly discharged.
  • There is interference from a powerful radio signal source.
  • The SmartKey is defective.
  • Check the battery using the battery check lamp and replace if necessary.
  • Use the emergency key to lock or unlock.
  • Have the SmartKey checked at a qualified specialist workshop.
You have lost a SmartKey.
  • Have the SmartKey deactivated at a qualified specialist workshop.
  • If necessary, have the mechanical lock changed as well.
    Opening and closing


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