EIS or EZS : Electronic Ignition Switch
Starting model year 1998, Mercedes introduced the DAS 3 system that used an encrypted data transfer method via Infared Receivers.
These ignition switches also led the way for the CAN network to be incorporated for majority of the modules in the car. The EIS acted as a Gateway or communication hub on the early cars.
Being the Network Gateway in the car, it held majority of the optional coding data. So it had two functions, one as the Immobilizer module and the other as a network traffic director.
Being one of the main players for the immobilizer circuit, it holds the encrypted data for all key tracks. Mercedes has 8 key tracks stored within the EIS. These each have 3 slots available for use. For example, if you have Key #1 for the car and you lose it, then you can order or make another Key #1 but in the second slot. This also applies to the other 7 key tracks.
The EIS has to verify the data in the keys as matching what it has stored. It then verifies that data with other control units that store key track data as well. Some other modules that store that data can be the ESL ( Electronic Steering Lock ) ESM ( Electronic Shifter Module ) ISM ( Intellegent Shift Module ) ME ( Motor Electronics or Engine ECU ) ETC ( Electronic Transmission Control unit ). Depending on the modules equiped in the vehicle, one or all may have this data stored. Before the car is allowed to start, all this data must be checked and matching for any actuation.
Early EIS versions had Motorola Version processing chips installed. These are known in the industry as HC705, HC908, HC912, HC9s12. Each version chip has a different way of protecting the data. Since the beginning of the 221 chassis S550 Mercedes, they introduced the NEC chip EIS. These chips increased the difficulty in reading and retreiving all the data needed to generate a new key for the car. These systems are also known as the FBS2 generation.
They then were superseeded by the FBS3 and the FBS4 immobilizer versions. With every update the level of complexity increases. The Diagspeed tool has allowed locksmiths and like trades to continue to be able to makes keys in these every so complex cars.
This has made the Diagspeed the leading tool for making Mercedes Keys