A key fizzles out in a man's hand, no longer working on his vehicle

Why won’t my Mercedes-Benz key turn in the ignition?

Mercedes-Benz Ignition and Key Problems

When things don’t work as they should, it’s inevitably frustrating. At moments like these, it’s important to remember to remain calm and mindful. If the frustration is not serving a purpose, let it go.

Once the frustration has dissipated, the problem on hand still remains to be solved. This is where the fun begins. First, the diagnosis: why won’t my Mercedes-Benz key turn in the ignition?


Further questions? Contact our Mercedes-Benz Service Center


There are two main scenarios that could cause your key to be unable to turn in the ignition. These are:

  1. Your key fob battery is low or empty. This prevents the Electronic Ignition System (EIS) from functioning.
  2. The Driver Authorization System (DAS) is not functioning, and thus failing to verify the key properly when inserted into the ignition.

First Possibility: Key Problems

Before dealing with the DAS or EIS, make sure the key itself is not the problem; try a spare key or get the key battery replaced. Keys go bad more often than EIS modules do. This is generally good news, because keys are much cheaper to replace than those complex technologies.

A gravestone flanked by blue skulls reads, "RIP Key Fob". A man on the right is sad and a man on the left holds out a key fob

Second Possibility: EIS or DAS Failure

Newer keys, called SmartKeys, have a transponder integrated into them. This fob remote both disables the anti-theft system when you unlock the car, and interacts with the Drive Authorization System, which verifies the key to make sure it is the right key to start the car.

Once the key is authorized, the steering column is unlocked. The key can be turned, and the Engine Control Unit is allowed to start the engine.

If there is a problem with either the EIS or DAS, unfortunately, the key will not be authorized to turn.

It’s funny how these problems don’t usually occur on Mercedes-Benz models in movies.

How can I fix my Electronic Ignition System or Driver Authorization System?

Certified Mercedes-Benz dealerships (such as ours) can perform the task of replacing the Electrical Ignition Module (EIS). For more information, contact us.

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