Brief description of components

The following components deliver signals to the instrument cluster:

• Outside temperature sensor 

  The ambient temperature sensor is connected to the junction box electronics (JBE).

  Wires from the JBE lead to the instrument cluster.

  The ambient temperature is displayed on the LCD display in the instrument cluster.

  When terminal 15 is OFF, the ambient temperature sensor will continue to measure the temperature for a maximum of 24 hours.

• Steering column switch cluster 

  Two switches are located on the turn-signal/main-beam switch on the steering column switch cluster (SZL): an axial switch and a rocker switch.

  The following contents can be called up with the two switches and shown on the LCD display in the instrument cluster:

  • On-board computer functions and Check-Control confirmation
  • Menu for the following functions (display is encoding-dependent, also in CCC or M-ASK, depending on equipment fitted):
    • Dim instrument illumination
    • Scroll Check-Control message
    • Check engine oil level
    • Run Flat Indicator initialization
    • Set time
    • Set date
    • CBS settings
    • Settings for Car and Key Memory (marketing terminology: Personal Profile)
• Footwell module 

  The footwell module (FRM) controls the interior and exterior lighting.

  From the footwell module, information is sent through the K-CAN, e.g. whether or not the indicator and warning lights stipulated by law need to be actuated.

• Junction box electronics or junction box 

  The junction box electronics send the following signals to the instrument cluster:

  • Coolant level (Check-Control message)
  • Washer fluid level (Check-Control message)
  • Fuel level via 2 fuel level sensors (used by instrument cluster to compute the Check-Control message)
  • Parking brake applied (general brake warning lamp)

  The junction box is also the gateway between the PT-CAN and the K-CAN. The PT-CAN is used, e.g. for DME/DDE and DSC messages.

  The K-CAN is used, e.g. for terminal control signals from the CAS control unit.

  The instrument cluster receives its power supply from the junction box terminals 30 and 31.

• Multiple restraint system 

  The multiple restraint system (MRS) is a bus participant on the K-CAN.

  The MRS control unit sends the message whether the airbag warning light or seat belt indicator light needs to be actuated.

• Digital engine electronics or digital diesel electronics 

  The DME/DDE supplies the following signals (for example) to the instrument cluster: Engine speed and injection rate.

  The message is sent through the PT-CAN and then through the K-CAN. The DME/DDE also indicates whether an exhaust-related fault has developed (actuation of emissions warning light).

• Dynamic Stability Control 

  The brake pad wear sensors are connected to the DSC control unit. The DSC also sends further messages to actuate indicator and warning lights in the instrument cluster:

  • ABS indicator and warning light.
  • DSC indicator and warning light.
  • DTC indicator light.
  • General brake warning light
• Electronic transmission control 

  On vehicles with automatic transmission:

  A signal from the EGS control unit causes the gear program display or gear indicator in manual mode to be shown in the LCD display.

  On vehicles with manual transmission:

  No gear indicator. The area is used (via encoding) for a larger on-board computer function display.

• Cruise control with brake function / active cruise control (E90/E91 only) 

  On vehicles with 6-cylinder engine and longitudinal dynamic management (LDM control unit):

  The set speed is transmitted by the LDM control unit to the instrument cluster on the PT-CAN and K-CAN.

  During active cruise control, an additional indicator light is activated as a distinguishing feature for cruise control with brake function. The distance to the vehicle in front is indicated with 3 bars. The set speed for active cruise control appears briefly in the LCD display (in addition to permanent display with the moving-disc instrument).

• Body CAN 

  The instrument cluster receives all other messages that could mean a display in the instrument cluster (e.g. Check-Control messages) through the body CAN (K-CAN).