This article was reviewed by the YOUCANIC editorial team.
If your vehicle does not recognize the key and displays a message such as “Key not recognized,” you most likely are using the wrong key or have a dead key fob . Common messages we see on newer vehicles include “Key does not belong to vehicle” and “Key Not Recognized.”
Other possible problems include a damaged key (even if it unlocks the doors), a bad All Activity Module (AAM), or a faulty Electronic Ignition Switch (EIS).
Start by making sure that you have the correct key. If you have a keyless start option, remove the START button from the ignition and insert the keyfob, or press the START button with the key to start the engine.
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You may have to hold the key next to the steering column on some models while pressing START. If you have a spare key, try starting the car with that key. You should try a few things if you get this error message.
Wet Key
If you drop the key in the water or wash it with your laundry, it may stop working. Sometimes, allowing the key to dry for a few hours will let you start the engine. Remove the battery (and the circuit board when possible) from the key and allow the key internals to dry.
Damaged Key
If the key was dropped to the ground, it might also stop working. The small coil inside the key can get damaged when the key is dropped. A Mercedes-Benz key typically doesn’t fail with a single drop but drops it several times, and you may end up with a key that won’t start or unlock the car.
If you remove the circuit board inside the keyfob, you should see a small coil. The coil is soldered at both ends. Inspect both ends and ensure they are still connected to the circuit board.
Try Spare Key
If you have a spare key, try starting the engine with the second key to see if it works.
If the second key starts the car, we know we have a bad key. A bad Mercedes-Benz key may be able to unlock doors but not start the engine. That’s because a Mercedes-Benz key sends two different signals. One is for opening doors, and the other RFID chip is used to authorize vehicle start. While it is unlikely to happen, it is still possible that the RFID chip integrated into the key is bad.
If the spare key does not work, the problem is not the keys but the car.
Supply Power to the Battery
The main car battery may be partially discharged. When this happens, several low-voltage fault codes get stored in the various control modules. More importantly, modules such as the Electronic Ignition System (EIS) may not have enough power to…
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