The immobilizer prevents your vehicle from being started without the correct SmartKey.

When leaving the vehicle, always take the SmartKey with you and lock the vehicle. The engine can be started by anyone with a valid SmartKey that is left inside the vehicle.

To activate with the SmartKey: remove the SmartKey from the ignition lock.
To activate with KEYLESS-GO: switch the ignition off and open the driver's door.
To deactivate: switch on the ignition.

The immobilizer is always deactivated when you start the engine.
In the event that the engine cannot be started when the starter battery is fully charged, the immobilizer may be faulty.
Contact an authorized Mercedes-Benz Center or call 1-800-FOR-MERCedes (in USA) or 1-800-387-0100 (in Canada).