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Mercedes Intermittent Ignition Problem


  • Mercedes-Benz key works intermittently. Key works properly when it is warm. When it is cold or the temperature drops below 20 degrees Celcius it stops working.
  • Key doesn’t start the car when cold.
  • Key and ignition work properly all day when it is warm.

Possible Cause

  • These symptoms are often caused by weak joints on the EIS (Electronic Ignition System). In same cases, these problems can be due to a defective SAM (Signal acquisition module).


If you are experiencing any of the problems described here you will need to identify whether the problem is the EIS or SAM module. To properly diagnose such problems you will need a diagnostic scanner such as iCarsoft MB II orAutTel MaxiDAS DS708.

Once you identify the defective module you can get it repaired in most cases. There are services that you can find online that will repair your old EIS and SAM module.

Turn igniton off and waitNote that your original EIS module can be repaired and reinstalled without needing any reprogramming. You can’t install a used EIS module in your Mercedes-Benz even if the unit has the same part number. EIS modules are locked to the vehicle and the VIN number stored in the unit has to match the car. Your other option would be to get a new EIS or SAM module from the dealer and have them perform the programming.

Related fault codes

  • B1000 – Control Unit N73 EIS / EZS Control Unit is defective.

One comment

  1. I have an issue with my keyless ignition. Most of the time it works fine. But sometimes it says not detecting the key. I’ve had the battery changed in the key so I know it’s not that.

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