If your vehicle is not recognizing 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 the key being damaged (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 in the ignition or press the START button with the key to start the engine.
You may have to hold the key next to the steering column on some models while you press START. If you have a spare key, try starting the car with that key. Here are a few things you should try if you get this error message.
If you dropped the key in the water or washed it with your laundry, the key 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.
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 from inside the keyfob, you should see a small coil. The coil is soldered at both ends. Inspect both ends and make sure 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 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 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 power up correctly and recognize the key. This scenario can be challenging to diagnose because when the car battery is practically discharged, the car lights and instrument cluster still power up.
You can connect a jump box (or jumper cables) to jump-start the car. Press unlock on the keyfob and try to start the engine. In some cases, jump-starting will allow the vehicle to recognize the key and enable you to start the engine.
Disconnect the negative battery terminal to reset the ECU. Resetting the ECU will sometimes allow the car to recognize the key. You may lose a few memory settings, such as the window auto-close feature and power seat memory, but those are very easy to set on your own.
Next, check all the fuses to ensure there are no blown fuses in the car.
Lastly, make sure to replace the key fob battery. It can be why your Mercedes-Benz does not recognize the key, especially on models with a keyless start. When you remove the START button and insert the key in the ignition, you should be able to start the engine even if the key fob battery is dead.
The tips in this guide work in most cases. If none of these tips helped, your vehicle must be diagnosed with a professional scanner. You can use a professional scanner such as the YOUCANIC Full System Scanner to diagnose all Mercedes-Benz control modules.
We hope you find the Key Does Not Belong to the Vehicle guide helpful. Check these troubleshooting and repair guides for more help on your vehicle.
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