How to sync the Mercedes Key fob?

This article will answer the following questions: how to sync the Mercedes Benz Key fob? When to sync the Mercedes Benz Key fob? Which steps to take if the Mercedes Benz key fob is not working?

How to sync the Mercedes Key fob?

The process of syncing the Mercedes Benz key fob to its vehicle is also known as personalising or pairing the key with the vehicle. It is a one time process and once the key is successfully synced the electric ignition lock will not ask to sync the key again even if the battery in the key drains completely.

Following is the procedure to sync the Mercedes Benz key fob:

  • Press the lock button on the key fob and check if the vehicle locks. The hazard lights will flash if the vehicle receives the drive authorization codes and the vehicle will lock
  • Press the unlock button on the key, the vehicle should unlock and hazards will flash once to indicate the vehicle is now unlocked.
  • Enter the vehicle and put the key in the electronic ignition lock and turn to position 2. A message ‘ please wait Key is pairing’ will appear on the information display in the instrument cluster.
  • When the message disappears then start the vehicle.

If the vehicle states it means the key has been successfully synced to the vehicle and the electronic ignition key will recognise it. Mercedes Benz cars use a very sophisticated drive authorization system that has rolling and hash codes.

Rolling codes are used for access authorisation which is used for entry into the vehicle and the hash codes are used for the drive authorization. Drive authorization system in Mercedes Benz cars consists of theft relevant components like engine control unit, electronic ignition lock, transmission control unit and in the latest model the electronic stability program control unit.

 The authorization codes are verified in the electronic ignition lock control unit which then sends start to enable signals to the other theft relevant components. All the theft-related components communicate with each other via the CAN network.

The latest model does not have a conventional ignition lock to put the key in then simply place the key in the centre console at the market position. There is a two way transmitting and receiving antenna in the centre console that can read the signals from the key. 

 Only the latest Benz models have an ignition lock located on the front passenger Floor or the dashboard.  The transmitting and receiving antenna in the centre console is directly connected to the electronic ignition lock control unit.  

There is an inductive coil built into the antenna which will supply power to the key if the battery in the key is completely dead.  antenna only charges the key for you seconds until the authorisation codes are exchanged.

When is it required to sync a Mercedes Benz key fob to the vehicle?

The process of syncing a Mercedes Benz key fob to the vehicle is a one-time process and usually, the electronic ignition key will recognise the replacement key or the spare key when it is inserted into the ignition lock. Async or pairing  might be required in the following situations:

  • When a replacement key or a spare key is programmed and inserted into the vehicle for the first time.
  • If the customer is using the additional or spare key of the vehicle for the first time.
  • If the vehicle battery drains completely and customers have to either jump start the car or replace the battery.

In some old Mercedes Benz models like the C class model series W202 with the second generation of the drive authorization system, the key used an infrared transmitter and receiver to verify the authorization codes. Green and red led lights on the rearview mirror and driver’s door handle indicated the current status of the immobiliser.

To sync the key in the second generation of the DAS, point the key at the centre mirror and keep the button on the key pressed. Both the red and green LED blinks and the key is synced to the immobiliser.

Which steps to take if the Mercedes Benz Key fob is not working?

The Mercedes Benz key fob has a transmitter and receiver antenna used for the keyless go system. If the Key is not locking and unlocking the vehicle, a low key battery could be the reason for the inoperative key. Hence, try to lock and unlock the key from the second key of the vehicle. 

If the second key is not available then replace the battery of the Key fob. The battery is located in the key and to replace it, remove the rear cover and slide the battery tray out. Insert the new battery and follow the positive and negative marks in the sliding tray. If the battery is not inserted correctly the Key fob will not work.

If The key fob does not work even after replacing the battery, make sure to check if the key belongs to the correct vehicle. Mercedes Benz uses an antenna amplifier with a built-in key identifier, if the key does not belong to the vehicle it will not unlock the car.

There can be an internal fault or a fault related to the drive authorization components, consult the nearest authorised workshop for further diagnosis. The diagnosis tool in the dealership can test the drive authorization system and identify the faulty component.

Conclusion

Mercedes Benz key fobs are reliable and usually will not need syncing to the drive authorisation system. Even if a key needs to be synced to the vehicle, the process happens very quickly and customers don’t have to wait to start the car.

FAQs: how to sync Mercedes key fobs?

Can I program a Mercedes Key fob myself?

It is not possible to program a Mercedes Benz key fob without a Xentry diagnosis tool and proper documentation. Mercedes Benz uses a very complex drive authorization system and all the authorization codes are located in a centralised vehicle database. You can directly order a program key from a dealership or an authorised dealership can program it for you.

How do you program a Mercedes Key?

A Mercedes Benz key is programmed by inserting the blank key into the ignition switch or a key station. A key station is a device similar to an ignition switch and it is used for programming a black key. Drive authorization generation four can even be programmed by an entry tool available at authorised dealerships.

How do I reset my Mercedes Key fob?

The programming of the Mercedes Benz key fob and its pairing with the intended vehicle is a non-reversible procedure. It is not possible to reset the Mercedes Benz Key fob. Even if the battery is removed, all drive authorization data is stored in the electronic ignition lock.

How do I fix my key fob not working?

If the key fob is not working, check if the low battery led light is blinking when you press the button on the key. Try to unlock the car from a closer distance and replace the battery. If the key fob is not working even after replacing the battery then there could be a malfunction in the key fob. Consult the nearest workshop for further diagnosis.

Why does my key fob not work after replacing the battery?

If the key fob does not work even after replacing the battery then there could be a malfunction in the drive authorization system of the vehicle. Check if the vehicle battery is okay and try to use a spare key. If the vehicle unlocks with a spare key then there is an internal fault in the key fob and it must be replaced to rectify the concern.

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