Monitoring of steering angle and steering-wheel turns

The steering column switch cluster (SZL) records the following information for the DSC functions:

• Steering angle
• Steering-angle rate
• Steering-wheel turn

The relative steering angle gives the angular position of the steering wheel. A steering angle of ± 180° can be measured. The information always remains stored, even when there is no current applied to the steering column switch cluster.

Zero calibration must be performed with the BMW diagnosis system in the following cases:

• Replacement of SZL (steering column switch cluster)
• Coil spring cassette replacement
• Replacement of DSC control unit
• Working on the steering

Information about steering-wheel rotations 

The signal from the steering-angle sensor is repeated every 360°. These signal repetitions are used to count the number of turns of the steering wheel.

The steering column switch cluster has a permanent power source via terminal 30. This allows steering wheel movements to be detected even when the ignition is OFF.

Following a power interruption, the information about the number of turns of the steering wheel is lost.

When a journey is started, the steering column switch cluster will again measure the number of turns of the steering wheel.

If this process has not been completed when a speed of approximately 25 km/h has been reached, the DSC indicator and warning light will light up (repeat the process by restarting).

During measurement, the steering column switch cluster uses various pieces of information, including data from the wheel-speed sensors on the front wheels.

Not all signals are processed in the steering column switch cluster. Some signals are simply looped through the steering column switch cluster (e.g.: driver's airbag, on-board computer function, horn).

Information is transmitted via the F-CAN (Chassis CAN) or via direct wires to the systems or affected control units.

The steering column switch cluster (SZL) is activated:

• From the outside via the wake-up wire (terminal 15 wake-up) with bus activation (e.g. when the driver's door is opened)
• From the inside by steering wheel movements

  (without bus activation, only for internal evaluation of the steering angle)

• From the inside by movement of the turn-signal/main-beam switch

  (without bus activation, SZL is only active as interface to FRM, e.g. when park lights are switched on)