Mercedes-Benz E-Class Quiz
Opening and Closing

Keys. Key battery

In this manual: Opening and Closing
Introduction — 5At a glance — 6Safety — 25Opening and Closing — 17Seats, steering wheel and mirrors — 12Lights and windshield wipers — 11Climate Control — 11Driving and parking — 44On-board computer and displays — 29Stowing and Useful Information. Good to Know — 1Stowing and Useful Information. Storage Options — 10Stowage and convenience features. Convenience features — 7Maintenance and care — 11Roadside assistance — 13Wheels and tires — 13Technical data — 13
~3min read

The key of the Mercedes E-Class (4th gen. W212, 2009–2016) is a small technical marvel that deserves your attention. Here you will learn what to observe when replacing the battery in order to maintain full functionality and prevent unexpected problems.

Checking the battery

Batterie kontrollieren

Press the buttonorpress.

  • If the battery indicator lamplights up briefly, the battery is OK.

    If the battery indicator lampdoes not light up briefly, the battery is discharged.

    Replacing the battery .

    Info

    If the key battery is checked within the vehicle's reception range, pressing the buttonoraccordingly
    • to lock or
    • to unlock the vehicle.

    You can have the battery replaced at any qualified workshop.

    Replacing the battery

    You will need a 3 V button cell of type CR 2025.

    Remove the emergency key from the key .
    Batterie wechseln

    The emergency keypress in the direction of the arrow into the opening of the key until thebattery compartment cover opens. Do not hold the battery compartment coverclosed while doing so.

    Remove the battery compartment covercarefully.
    Batterie wechseln

    Tap the key against the palm of your hand until the batteryfalls out of the key.

    Insert the new battery with the positive terminal facing up. Use a lint-free cloth to do so.

    Make sure the surface of the battery is free of lint, grease or other contaminants.

    Remove the battery compartment coverInsert the front tabs into the housing first and press it closed.

    The emergency keyinsert into the key.

    Check the function of all buttons on the key with the vehicle.

    Problems with the key

    Problem Possible causes/consequences and solutions
    You cannot lock or unlock the vehicle with the key. The key battery is weak or discharged.

    Check the key battery and replace it if necessary.

    If this is not possible:

    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 at a qualified workshop.
    You cannot lock or unlock the vehicle using KEYLESS-GO. The key battery is weak or discharged.

    Check the key battery and replace it if necessary.

    If this is not possible:

    Unlock or lock the vehicle with the emergency key.

    A strong radio source is causing interference.

    Unlock or lock the vehicle with the emergency key.

    KEYLESS-GO is defective.

    Lock or unlock the vehicle using the remote control function of the key.

    Have the vehicle and key checked at a qualified workshop.

    If the vehicle also cannot be locked or unlocked using the remote control function:

    Unlock or lock the vehicle with the emergency key.

    Have the vehicle and key checked at a qualified workshop.
    You have lost a key. Have the key blocked at a qualified workshop.

    Report the loss to your vehicle insurer immediately.

    If necessary, have the mechanical lock replaced.
    You have lost the emergency key. Report the loss to your vehicle insurer immediately.

    If necessary, have the mechanical lock replaced.
    The engine cannot be started with the key. The vehicle electrical system voltage is too low.

    Switch off unnecessary consumers, such as seat heating or interior lighting, and try to start the engine again.

    If this does not work:

    Check the starter battery and charge it if necessary.

    or

    Have a jump start performed.

    or

    Contact a qualified workshop.
    Vehicles with manual transmission only:

    The engine cannot be started with the key.

    		 The steering lock is mechanically jammed.

    Remove the key and reinsert it into the ignition lock. While doing so, turn the steering wheel in both directions.
    The engine cannot be started using KEYLESS-GO. The key is inside the vehicle. The vehicle is locked.

    Unlock the vehicle and try to start it again.

    A strong radio source is causing interference.

    Start the vehicle with the key in the ignition lock.

    The Mercedes E-Class W212 (model years 2009–2016) places great emphasis on ease of use, including when replacing the key battery. The battery can be replaced in just a few simple steps, and the key remains ready for use.

    Practical instructions and clear notes help you act quickly when needed. This ensures the familiar comfort of the E-Class W212 is maintained at all times.

    These well-thought-out details show how Mercedes-Benz makes everyday driving easier for its drivers, right down to the smallest detail.

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