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What you will need when replacing a Mercedes-Benz Key or EIS (Electronic Ignition Switch) with a used one.

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Mercedes-Benz vehicles manufactured since 1998 and newer use what is called Drive Authorization System (DAS) to validate the correct key is being used to start the engine. The key used by the owner contains a small chip called  EEPROM (electrically erasable programmable read-only memory) which stores a fixed serial number and a rolling code.

The key that the owner has includes a sequential code, unique to your vehicle, and when inserted into the ignition, the car runs a series of tests such as verifying VIN number in all DAS modules and check the rolling code before the car can be started. 

Drive Authorization System (DAS) main function is to prevent theft which is the reason why Mercedes-Benz codes the vehicle VIN in a number of control units.  

The Electronic Ignition Switch of the Mercedes-Benz C-Class W204

Replacing the Ignition Switch (EIS) on a  Mercedes-Benz is not that difficult. The problem is that a used EIS needs to be programmed to change the VIN stored and erase the data from the previous vehicle to the new one. That's because EIS is part of the drive authorization system (DAS) which is designed to prevent vehicle theft.

Only specialized auto repair shops will be able to code a used EIS to work on another vehicle.  Mercedes-Benz dealership or repair shops that are not familiar with Mercedes-Benz vehicles will not code a used EIS, instead will install a new EIS and program it. 

DAS is a network of control modules, each of which calculates the drive authorization code independently. For example, control modules involved in DAS verification are:

  • Electronic Ignition Switch (EIS)
  • Electronic ignition lock control module. 
  • Engine control module (ECM).
  • Transmission control module (TCM).
  • Intelligent servo module for DIRECT SELECT.

The only way to get a used Mercedes-Benz EIS from a donor vehicle to work on another car is to get the data of the previous vehicle erased from that module. This process is often called VIRGINIZE the module and can be performed by independent repair shops.

The Key of the Mercedes-Benz C-Class W204.

For the key or Electronic Ignition Switch (EIS) to work, you need to program the unit or ship it to a specialty shop where they can change the VIN of the previous vehicle to the VIN of your vehicle, then they will erase the stored data from the donor vehicle. After that, you can install the ignition switch in your vehicle.

Further programming may be required to get the EIS to work properly. 

For example, the C-Class W204 has a steering column lock that needs to be programmed. Many models such as the 2001 S-Class and up have the gear shift module that is coded and needs to be programmed as well.

The Steering Lock Mechanism of the Mercedes-Benz C-Class W204

The changing of code and clearing data from the donor vehicle is a preventive measure for vehicle theft.

The gear shifter of the Mercedes-Benz C-Class W203.

If you do not replace the VIN of the unit or erase the code of the previous vehicle these are probable causes that will show on the vehicle.

  • Cannot Turn the Key
  • Cannot Start the Vehicle
  • Can Turn the Key but the Vehicle does not start
  • Ignition Switch Faulty Codes



Servicing Mercedes-Benz DAS Anti-Theft Systems What you will need when replacing a Mercedes-Benz Key or EIS (Electronic Ignition Switch) with a used one.