Mercedes-Benz C-Class Manuals

Mercedes Benz C-Class (W204) 2007 - 2014 Training Manual: On-Board Electrical System Management

The on-board electrical system management is integrated into the rear SAM control unit with fuse and relay module (N10/2) and is responsible for ensuring the supply to all electrical consumers, based on need and situation, as well as the vehicle's ability to start.

The following components play a decisive role in the implementation of the on-board electrical system management:

  • On-board electrical system battery (G1)
  • Alternator (G2)
  • Battery sensor (B95)
  • Rear SAM control unit with fuse and relay module (N10/2)
  • ME-SFI [ME] control unit (N3/10)
  • Prefuse box F32 with quiescent current cutout relay (F32K2)

Prefuse box F32 with

  • Prefuses
  • Quiescent current cutout relay
  • Pyrofuse
  • Jump-starting point

Information for Service

The components in the prefuse box cannot be replaced individually.

Prefuse box F32

Mercedes Benz C-Class. On-Board Electrical System Management

Battery sensor (B95)

Mercedes Benz C-Class. On-Board Electrical System Management


The battery sensor (B95) and the rear SAM are responsible for the on-board electrical system management. Installed directly at the negative terminal, the battery sensor measures voltage, current and temperature at the on-board electrical system battery and uses these to evaluate the battery's status.

The following measures can be introduced to stabilize the on-board electrical system:

  • Specification of the optimum charging voltage
  • Gradual consumer shutoff (no display in instrument cluster)
  • Idle speed increase

The battery sensor is also used for checking the quiescent current.

Quiescent current cutout relay


The quiescent current cutout relay is a bistable relay. It separates the consumers and components at circuit 30g. If the ignition is turned off or the ignition key is removed, the quiescent current switch relay opens after 6 hours or it opens if the on-board power supply voltage falls below 11.8 V. The quiescent current cutout relay is actuated by the rear SAM.



A pyrofuse, which disconnects the starter and alternator line from the battery in the event of a collision, is used in the prefuse box. It is activated by the ARAMIS control unit (airbag).


There are three different light systems to choose from for model series 204:

  • H7 halogen headlamps (standard)
  • Bi-xenon headlamps with cornering illumination (SA 614)
  • Intelligent Light System (SA 622)

Also installed for all three light systems is a light sensor, which permits the automatic exterior light control via the two SAM control units.

In the basic lighting version, the mirror turn signal and the center high-mounted brake lamp are designed as LEDs, in vehicles with intelligent light system (ILS) the rear turn signal lamps are also fitted with LEDs. The brake light has a "contactless" brake light switch and is designed as an adaptive brake light.

The familiar functions of emergency light and substitute light are also implemented. In vehicles with ILS the following extended functions are also implemented:

  • Dynamic curve illumination
  • Cornering illumination
  • Dynamic headlamp range control
  • Country light (new)
  • Motorway lights (new)
  • Extended fog light function (new)

Mercedes Benz C-Class. Illumination

Information for Service

The control units for bi-xenon headlamps can be replaced separately.


    Lamp unit equipment

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    Mercedes Benz C-Class (W204) 2007 - 2014 Training Manual

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