A problem that Mercedes-Benz owners may face is the key no longer turns in the ignition. This issue is often caused either by a defective key, bad shifter module, a failed Electronic Ignition Switch (EIS) also known as the EIS-EZS or a bad steering lock module (ESL). This problem can affect various Mercedes-Benz models including E-Class, S-Class, C-Class, CLK-Class, ML-Class, SL-Class, etc.
Possible symptoms of a failed Mercedes-Benz include:
• Key does not turn in the ignition due to failed EIS
• Key doesn’t turn during cold weather
• Key may turn, but the instrument cluster lights don’t turn on
• Unable To Turn The Key, Unable To Start The Car
• Can turn the key but car won’t start
• Mercedes key intermittently works
• Push start button no longer works
Mercedes-Benz ignition switch (often referred as immobilizer module) can become faulty and in some cases due to user error. For example, some common reasons why the ignition module failed are:
• Low battery voltage
• Power surge due
• Connecting jump starting cables while key is in the ignition.
During any of the above scenarios, the EIS-EZS may lose its memory. While it can be diagnosed with Start Diagnostic Scanner used at dealerships, it can’t be repaired with this scanner. Mercedes dealers don’t repairer a bad EIS-EZS module. They will recommend that the module be replaced. That’s not necessarily the only solution, see alternatives below.
How to fix Mercedes Ignition Switch Problems
These symptoms can very well be caused by a defective key. If you have a spare key try to see if you are experiencing the same symptoms with the other key. If the other key works, keep using it for a couple of weeks to verify that the issue is really the key and not the EIS.
Try scanning your Mercedes-Benz for fault codes. Ideally using a Start Diagnostic Scanner. This scanner should still retrieve fault codes when the ignition is off. The only issue here is that if you can’t turn on the ignition, you can’t power on the OBD2 port and the scanner. If the ignition turns on intermittently, consider yourself lucky and scan for codes. Hopefully, there are fault codes that will point you to the problem.
Diagnosing Mercedes ignition problems isn’t a simple DIY job. You may consider taking your car to the dealer or an independent shop and have them troubleshoot the problem. If they come to the conclusion that the Ignition Switch (EIS-EZS) is the culprit you will be told that the switch will need to be replaced. This is an expensive repair that can cost several hundred dollars. You have a few options here. Have the dealer install a new ignition switch, and they will program it to match the VIN of your Mercedes-Benz. Many owners go the route of installing ignition switch, ECU, shifter module and other parts from a donor vehicle. You can’t replace the ignition switch only with one from a used Mercedes-Benz. Several parts need to swapped because the stored VIN needs to be the same in all of them.
There is also a third option, and it may be the cheapest way to fix Mercedes ignition switch module. There are companies that can repair Mercedes-Benz ignition modules. You will need to remove the ignition module from your Mercedes-Benz and ship it one of these companies that can test and repair the EIS-EZS. Once the module is repaired it is returned to you. Besides the fact that this is a lot cheaper than installing a new ignition module, it also doesn’t require any programming or coding. The VIN stored in the Ignition Module (EIS-EZS) matches that of the car; it’s your old module after all. Just install it and you are ready to go.
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