Mercedes EIS Repair – EZS Immobiliser Key Module – ESL + KEY Repair Service

Mercedes EIS (Electronic Ignition Switch) Modules

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 and we’re getting units sent in 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

Below we have compiled an extensive list of vehicles which we have already seen fitted with the EIS and have had units in for repairs. Don’t worry if your vehicle is not listed as this is not a complete list.

Mercedes EIS / EZS Immobiliser Key Module Problems

• 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

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

Mercedes-Benz EIS / EZS (Electronic Ignition Switch) Module Repairs

We can remanufacture 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. When the unit is returned to you, you will not be required to reprogram or re-calibrate the unit – simply plug & play.

After we have repaired your EIS module, you will be able to insert the key, turn the key and start the vehicle with no troubles at all. We do however recommend that you check the battery supply voltage and wiring to the EIS unit prior to installation to ensure there are no faults on the vehicle which could potentially cause failure of the replacement / repaired unit.

All repaired EIS modules are returned with our full Lifetime warranty.

Commonly Asked Questions

• What if it is my ESL or Key that’s faulty – What should I do?
  We always recommend sending all three parts to us so that we can independently test the units and also test them in circuit alongside each other. We can remanufacture all three parts if required and any repaired units are returned with a Lifetime warranty for complete peace of mind.
• Will Mercedes EIS programming be required?
  No – we backup all the programming data before remanufacturing the units. Our remanufactured units are returned fully plug & play and will self-calibrate when fitted back to the vehicle.
• Can you offer a Mercedes EIS replacement?
  Certainly – if your unit is for any reason beyond repair, we can offer a replacement unit and program it on our bench so that no further coding is required when fitting to the vehicle.
• I’ve been told my model of Mercedes does not have an ESL?
  Not all Models are fitted with an ESL, some models are controlled through the auto gearbox system and in such cases we will only require the EIS and ignition Key.
• Do you have a Mercedes EIS removal guide?
  No – we do not offer any removal / fitting instructions and always recommend that the removal and fitting is carried out by a competent technician.