You insert the key in the ignition of your Mercedes but nothing hapens, You cant turn the key, or maybe you Can you hear a juddering noise from the Electronic Steering Lock (ESL)? Don't worry, we can help.

We can test your ignition module (EIS), Electronic Steering Lock (ESL) and your keys

The Mercedes EIS (Electronic Ignition Switch) system is great in theory, the hardware being the switch is like a small socket in the dash to insert your key into – only, it is not a traditional looking key. It is more like a plastic lego-brick with what looks like an infra-red panel at the face of it which is inserted into the EIS socket on the dash. The key has a sequential code to ensure the vehicle is not stolen.

The vehicle will instantaneously carry out a sequence of test handshakes to ensure the correct key has been inserted. Each time the key is inserted, the EIS system will check the key and then ask the ESL (Electronic Steering Lock) system for verification that it accepts the correct key is being used. The ESL system will then look to see if the Engine ECU (Electronic Control Unit) agrees that this is the authorised key being used. – Then and only then, when all three control units agree it is the correct authorised key being used, will it allow the “Turn & Start” function to be activated.

Which Model Mercedes Has The EIS Module

The EIS module is factory fitted to almost all models right across the board from C-Class C220 Mercedes to ML’s and E350 Mercedes. You can expect the EIS module to be supported and installed on the following Chassis list:

W164 / W168 / W169 / W202 / W203 / W204 / W208 / W209 / W210 / W211 / W212 / W215 / W219 / W220 / W221 / W230 / W639 / W906

Mercedes EIS / EZS Immobiliser Key Module Problems

  • Key doesn't turn in the Mercedes Electronic Ignition Switch (EIS)
  • Not releasing the ESL (Electronic Steering Lock) when the key is Inserted
  • Key turns in the Mercedes EIS but the ignition lights on the instrument cluster doesn't switch on
  • Key sometimes doesn't turn in the Mercedes EIS
  • Incorrect programming by an incompetent garage/mechanic

EIS Unit Faults

If the EIS unit becomes faulty, the “Turn & Start” function will be de-activated and the module will be locked for security purposes. This will stop the vehicle from starting. It is very unfortunate but also a very common problem as there are many reasons as to why these units are failing – most are due to human error. Some of the most common reasons are listed below:

  • Jump Starting Whilst Key Is Inserted
  • Power Surge
  • Low Battery Voltage

All of the above can cause memory loss to the EIS module and it cannot be repaired or re-flashed using the Mercedes STAR diagnostic system. At this point, you would have been advised to purchase a new unit which can work out extremely expensive when working out the total bill with programming and labour inclusive with VAT.

One of the main problems is the Motorola CPU chip which fails, even the newer batch of EIS modules have the same processor fitted so fitting a new module won't solve the problem entirely.

The EIS holds vital Key data and links to the ECU and ESL (Electronic Steering Lock) and also acts as a central gateway to other vehicle electrics, Meaning eis and key faults could seem to cause other system faults.

Many EIS's can be easily fixed, with replacement parts or a service exchange unit - If a unit cannot be repaired we can supply a replacement in most cases

Contact The Car Key Centre