You can no longer lock or unlock the vehicle with the key.
The key battery is low or discharged.
Try again to lock or unlock the vehicle using the key's remote function. To do so, point the end of the key at the driver's door handle while standing right next to it, then press the buttonor the button .
If the attempt does not succeed:
Check the key battery and replace it if necessary .
Unlock or lock the vehicle with the emergency key.
The key is defective.
Unlock or lock the vehicle with the emergency key.
Have the key checked by a qualified workshop.
You have lost a key.
Have the key blocked by a qualified workshop.
Report the loss to the vehicle insurer immediately.
Have the locks replaced if necessary.
You have lost the emergency key.
Report the loss to the vehicle insurer immediately.
Have the locks replaced if necessary.
You cannot start the engine with the key.
The vehicle electrical system voltage is too low.
Switch off non-essential consumers (such as seat heating or interior lighting), then try starting the engine again.
If the attempt does not succeed:
Check the starter battery and recharge it if necessary .
Try jump starting .
Contact a qualified workshop.
You cannot start the engine with the key.
The steering is mechanically locked.
Remove the key and reinsert it into the ignition switch. At the same time, turn the steering wheel in both directions.
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Test yourself
A quick Mercedes-Benz B-Class quiz: every answer comes with an explanation and a link to the manual page.
or the button 
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