Brief description of components

The steering column switch cluster (SZL) is connected to the vehicle wiring harness via 2 plug connectors.

The steering column switch cluster consists of the following components:

• Evaluation electronics 

  The evaluation electronics analyze the signals from the components and send them as CAN messages on the F-CAN.

  The evaluation electronics include the following components:

  • Microprocessor
  • Power supply
  • F-CAN connection
  • Interfaces for optical and electrical input signals
• Steering-angle sensor 

  The steering-angle sensor optically detects the steering angle turned at the steering wheel by means of an encoded disc.

  The data is read and analyzed by the evaluation electronics. The data is transmitted directly to the DSC via the F-CAN. (F-CAN = Chassis CAN; DSC = Dynamic Stability Control.)

  Signal path:

  SZL -> F-CAN -> DSC

• Steering column stalk 

  The lever positions of all steering column stalks are optically monitored.

  The actions of pressing the buttons, turning the thumbwheels and pressing the rocker switches are detected by switching mats. The switching mats forward the position of the buttons and thumbwheels as voltage signals.

  Depending on the vehicle's equipment, the steering column switch cluster (SZL) could have the following steering column stalks:

  • Wiper/washer switch

    The switch signals are read into the steering column switch cluster where they are evaluated. The evaluated switch signals are emitted onto the F-CAN as a CAN message (It is only possible to check the switch positions with the BMW diagnosis system via DSC as the steering column switch cluster is not directly connected to the diagnosis system).

  • Cruise-control system steering column stalk

    The switch signals are read into the steering column switch cluster where they are evaluated. The evaluated switch signals are emitted onto the F-CAN as a CAN message (It is only possible to check the switch positions with the BMW diagnosis system via DSC as the steering column switch cluster is not directly connected to the diagnosis system).

  • Turn-signal/main-beam switch

    The switch signals are read into the steering column switch cluster where they are evaluated. The evaluated switch signals are resistance-encoded and transmitted from the steering column switch cluster by direct wires to the FRM (footwell module).

    The signals for the on-board computer functions are transmitted by a direct wire to the instrument cluster (KOMBI).

• Coil spring cassette 

  The coil spring cassette has the task of transferring electrical signals to or from the steering wheel.

  The signals are transferred as follows:

  • Airbag unit (signals to steering wheel)

    Signal path:

    MRS control unit -> SZL (signal simply looped through) -> Coil spring -> Airbag unit

  • Horn (signal from steering wheel)

    Signal path:

    Horn switch -> SZL (signal simply looped through) -> Junction box

  • Multifunction buttons (signal from steering wheel)

    Signal path:

    Multifunction buttons -> SZL -> F-CAN -> Junction box electronics (signal simply looped through) -> F-CAN -> DSC control unit (serves as gateway) ->

    PT-CAN -> Junction box electronics (serves as gateway) -> K-CAN -> Audio system

    (check switch positions with BMW diagnostic system using DSC)

The control units involved in the functions of the steering column switch cluster are as follows:

• DSC: Dynamic Stability Control 

  The steering column switch cluster (SZL) does not have its own fault memory. All fault data for the steering column switch cluster are stored in the DSC control unit.

  The DSC is connected to the steering column switch cluster via the F-CAN (chassis CAN).

• JBE: Junction box electronics 

  The junction box electronics unit is the data interface (= gateway) between the K-CAN and the PT-CAN. (K-CAN = Body CAN; PT-CAN = Powertrain CAN).

  Signals from the F-CAN (Chassis CAN) are simply looped through. This means: Signals from the F-CAN are not received or evaluated by the junction box electronics. The F-CAN cables are simply routed through the junction box housing.

  The junction box consists of the junction box electronics and the electrical distribution center.

• FRM: Footwell module 

  The footwell module controls the vehicle lighting. The footwell module is connected to the steering column switch cluster (SZL) by direct wires.

• CAS: Car Access System 

  The Care Access System reactivates the control units on the PT-CAN via the wake-up wire (terminal 15 wake-up).

• KOMBI: Instrument cluster 

  Information on the on-board computer functions can be called up via the on-board computer button (BC button) and the rocker switch. (The BC button and the rocker switch are integrated into the turn-signal/main-beam switch).

  The contents are displayed in the LCD display in the instrument cluster.

  The signals for the on-board computer functions are transmitted by a direct wire from the SZL to the instrument cluster.