Security System

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SKREEM (Sentry Key REmote Entry Module)

Location: behind the instrument cluster / gauges. You can only access it by removing the cluster.

This component reads the transponder inside the key using a transponder ring mounted in front of the ignition key (the silver ring).

Additionally, it also uses an antenna to provide remote locking functionality.

Most of this data is directly communicated over CAN-C.

Connected to:

  • Transponder ring antenna
  • Remote keyless entry antenna
  • Driver side lock switch (US only, for unlocking with valet key)
  • Remote Keyless Entry relay (for flashing lights)
  • Body Control Module (door lock switch senses, Remote Keyless Entry status output)

There is a known issue with these modules, causing them to corrupt themselves after many times of locking/unlocking, possibly when battery is low. It is not common, but if it happens, you would not be able to start your car. Contacting The Mercedes Swap Shop is your best bet on getting the car back in working order, as they also have a permanent fix for this issue.

Powertrain Control Module (PCM/ECU/ECM)

Location: next to the battery, inside the box, next to the RCM, silver module.

This module, of course, uses the SKREEM/BCM information, and uses it for immobilizing the car. This module also tells the instrument cluster (when coded) "Start error" when it was unable to authenticate with the SKREEM / key.

Central Locking Pump / Security Sytem Module (CLP/SSM)

Location: next to the Anti-Theft Tow Sensor, inside the trunk under the carpet and foam, wrapped in a yellow-ish foam like material.

Connected to:

  • Door ajar sensors
  • Fog lamp switch
  • Tail lights
  • Liftgate lock
  • Glove box
  • Rear window defogger
  • Anti-Theft Tow Sensor
  • Tonneau cover
  • Hood ajar sensor
  • Siren
  • Intrusion sensor (UK only)
  • Tow-Away alarm switch (in console)

Additionally, it provides vacuum for locking/unlocking the doors, trunk, and fuel door.

The modules location is prone to getting wet, causing it to malfunction, triggering the alarm. Water can damage the pump, causing the vacuum lock/unlock feature to stop working. The foam is used to reduce noise of the vacuum pump.


Location: under the wiper cowl, in a metal encasing.

Controlled by the CLP/SSM, it'll get updated when the car is locked, unlocked, and triggered the alarm. There is 1 model of this siren that beeps when you lock or unlock the car, which is A1718202526.

There is a Varta battery that can leak and corrode the PCB, causing it to trigger the siren/alarm.

Anti-Theft Tow Sensor

Location: Next to the CLP/SSM, inside the trunk under the carpet and foam, on the right side, mounted on a bracket.

This module checks if the car is inclining while locked, which would mean the car is being towed away, making the CLP/SSM trigger the alarm in the process.

The modules location is prone to getting wet, causing it to malfunction, triggering the alarm.

You can use the interior tow-away button to disable this feature.

Intrusion Sensor

Location: mounted inside the interior lightning component, near the rear view mirror.

This component was only installed in UK cars, in combination with ultrasonic sensors to detect movement inside the car.