How to Start a Mercedes-Benz with a Dead Key Fob
Starting Your Mercedes-Benz
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To start a Mercedes-Benz that uses the tapered SmartKey style, the engine Start / Stop ignition button must be removed. It appears to ‘float’ above the dashboard and is easily pulled away from the ignition lock. Insert the tapered end of the KEYLESS-GO key in the ignition lock and turn it to start and operate old school style.
Beginning in 2017, the ignition lock in AMG roadsters and coupes is found at the back of the center console storage area, as shown in the image. Insert the tapered key fob into the ignition lock and turn it to start and operate old school style.
In 2019, the AMG gets the new SmartKey, described next.
AMG Back-up Slot
Models using the new, rounded SmartKey fob styles , shown to the left, require that the fob be placed in a back up location or slot. These models, as of the 2019 model year, are the AMG, C-Class, E-Class and S-Class.
Warning! Do NOT attempt to remove the Start / Stop ignition button!
C-Class Back-up Slot
E-Class Back-up Slot
The back up slot in each model is found at the very front of the center console. Each slot is slightly different depending on the model, and an image from each model is shown here.
Each slot is marked by the image of a metal key with lines radiating from it, except for the C-Class, which has an image of the SmartKey fob itself (left).
S-Class Back-up Slot
Make sure that the slot is empty. Remove the SmartKey fob from the key ring and slide or place the fob into the slot with its buttons facing up. You can now start the car as normal. The car will recognize the key fob even if the fob’s internal battery is dead.
The new SmartKey fob style had spread through nearly the entire product line by the 2019 model year. However, the mark (the image of a metal key with lines radiating from it) is found in or near cup holders, which are at the front of the center console. See the two images at left. The 2021 S-Class Maybach uses the rear cup holder as well (second image) as well as a newer key fob. It is similar to the one shown above.
Also in 2019, Mercedes-Benz introduced the first of its electric and electrified models, the GLC 350e. And while the mark is also found in the cup holder, it too uses the image of the SmartKey (see the image to the right), like the updated C-Class models noted above. This will likely take over all model lines with time.
Finally come a small number of exceptions. Since 2019, the GLE and GLS SUVS use a slot, with the mark of a key with lines radiating from it, is found inside the center console storage area in the front. G-Class SUVs joined them in 2024. See the image to the left. Drop the key fob into the slot and start the vehicle as normal.
Note: For reasons unknown, all the Mercedes models we’ve tested have s light delay built in after the start/stop button is pushed and the key fob being recognized. Not to worry…
You can see videos of the open and start processes here, as well as key fob battery replacement.
Note: If you have made an attempt to start the vehicle without success, there may be residual pressure in the brake system and a new warning light may appear (left) or text message to Step on the Brake. Press the brake pedal very, very hard when trying to start the vehicle again to be sure that the release switch behind the pedal is engaged. Or wait a few minutes and try again.
… Return to Part I, Getting in
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Remember that only proper service and repair procedures will ensure the safe and reliable operation of your car. In addition, proper safety procedures and precautions, such as the use of safety goggles, the right tools and the equipment should be followed at all times to eliminate the possibility of personal injury or improper service which could damage the vehicle or compromise its safety.
These posts are for information sharing purposes only, and should not be used in lieu of an OEM service manual or factory authorized service procedure. We are not in the auto repair business nor do we publish automotive service manuals. Nothing we include on these pages and posts has been reviewed, approved or authorized by any vehicle manufacturer.
Technology is always changing and what is current and accurate today may be literally out-of-date and inaccurate tomorrow. And when it comes to the current state of flux in the auto industry, nothing is more true.
The author has 25 years of automotive experience and has assembled the most extensive collection of symbols and warning lights anywhere (over 1,000!) and can help you open and start any keyless start car with a dead key fob battery. BA, St. Joseph’s College, ME: MS, Rensselaer Polytechnic Institute, NY
Mercedes-Benz now features two SmartKey styles. The original and most common style is tapered, like the one shown to the right. To retrieve the mechanical key, slide the release catch found near the top of the fob in the direction of the arrow and pull the mechanical key away from the SmartKey (remote control or ‘clicker’).
In 2017, a second, rounded SmartKey style was introduced in the E-Class sedan, and is shown to the right. It migrated to S-Class sedans in 2018 and is found in all 2018 E-Class models.
Make sure the handle of the mechanical key is pointed away from the paint. Insert the key into the opening (black arrow) underneath the cap as far as it will go. Hold the door handle out. Pull the cap that is now on the mechanical key as straight as possible away from the vehicle until it releases.
The 2021 Maybach adds flush door handles. This has now been added to AMG and EQS models in 2023, EQE, E-Class, S-Class and C-Class models in 2024.
Finally, the 2023 CLE Cabriolet and 2024 GLC models employ yet another method to hide the key hole. Pulling the driver’s door handle to the open position reveal the key hole underneath the back of the handle. Simply insert the key and turn and you’ll be inside. And yet again, the alarm will likely sound, but it will go off when the car is started.