Mercedes Ignition EZS/EIS repair 

Mercedes EIS/EZS electronic system is like vehicle heart (Electronic Ignition Switch) but sometimes fails making big trouble for us. 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.

mercedes ezs price

Mercedes ignition common faults

  • Unable To Turn The  Key

  • Unable To Start The Car

  • Unable To Unlock Steering Lock

  • Can Turn The Key – But Car Won’t Start

  • Intermittent Ignition Key Faults

  • Won’t Start When Cold

mercedes Ignition repair

Reasons of the EZS failure

  • Jump Starting while key insterted

  • Power Surge

  • Low Battery Voltage 

  • Corrosion 

  • Faulty chip


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, it’s how you look after the vehicle which plays a big part.

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:

Re-manufacture Ignition module

We are able repair your existing EIS Module unit and save you a lot of money. We thoroughly test & repair all EIS modules to ensure we locate the faults and rectify them completely. 

After your EIS module has been repaired , you will be able to insert the key, turn  and start the vehicle with no problems whatsoever. Before plug the EZS back we always making sure there are all prerequisites are made regards the right power supply.