What is the EIS on a Mercedes?
Benz EIS Stands For Electronic Ignition Switch. The hardware is the switch into which the key is inserted but the key is not a key in the traditional sense, it is more like a plastic Lego brick
which fits into the socket in the dash board.
The key has a sequential code rich rolls on each time it is used so that the car cannot be stolen.
Every time the key is inserted the EIS, EIS checks the key and then asks the ESL (electronic steering lock) if it is happy with this key if ESL is OK it then asks engine
ECU (electronic control unit) if it agrees that this is the autherised key.
Only if all three control units agree that it is the correct autherised key is the turn and start function allowed.