How It Works
DSC needs the steering angle for its regulation function. The steering angles detected by the sliding contacts (2 voltage values) make up a complete turn of the steering wheel. Once the steering wheel has been turned through 360°, the voltage values are repeated. The steering-angle sensor thus also counts the number of turns of the steering wheel.
The entire steering angle measured by the steering-angle sensor is made up of:
- Steering-angle sensor correction value:
This correction value determines the straight-ahead position of the steering wheel. The correction value is defined and stored when the steering-angle sensor is calibrated.
- Current measured steering angle
- Number of turns of steering wheel
The steering angle, including the number of turns of the steering wheel, must be available when the ignition is switched ON. For this reason, the steering column switch cluster (SZL), and with it the steering-angle sensor, has permanent current via terminal 30. This allows steering movements to be registered even when terminal R is switched OFF.
Open circuits would cause the number of turns of the steering wheel stored in the steering-angle sensor to be lost. To ensure that the steering-angle sensor remains functional even in the event of an open circuit, the DSC control unit "learns" the steering angle via a plausibility check (initialisation). The DSC control unit computes the steering angle from the wheel speeds on the front axle. The plausibility check compares these signals with those from other sensors to recognise whether the vehicle is operating with an incorrectly calibrated steering-angle sensor.
If initialisation is unsuccessful after starting up to a speed threshold of approx. 25 km/h, then the following happens:
- DSC is deactivated
- The DSC warning light comes on
- A fault entry is stored in the DSC control unit (not in the steering-angle sensor)
If the steering-angle sensor fails, ABS will remain active.