Steering angle sensor

The functioning of the DSC system and various other vehicle control systems requires knowledge of the overall steering wheel angle. The overall steering wheel angle is measured by the steering angle sensor. The software and hardware for the steering angle sensor is integrated in the steering column control centre. The sensor function is the same as that of the previous sensor.

Brief description of components

Sliding contact

The steering-angle sensor has two potentiometers offset by 90 degrees. The steering-wheel angle determined by these two potentiometers covers one full steering-wheel turn; each of these signals is repeated after +/- 180 degrees. The steering angle sensor knows this and counts the steering-wheel revolutions accordingly.

Control unit

The control unit for the steering angle sensor is integrated in the steering column control centre.

Main functions

The total steering angle output by the steering-angle sensor is composed of the following three values:

• Correction value of the steering-angle sensor This correction value sets the zero-degree position of the steering wheel. The correction value is set and stored on calibration of the steering-angle sensor. The correction value results from the difference between the steering angle of the potentiometer and zero degrees.
  
• Current measured steering angle of the potentiometer
  
• Number of steering-wheel turns
  

So that the total steering wheel angle is available at all times, uninterrupted measurement of all steering wheel movements is required, also if the vehicle is at a standstill. In order to achieve this, the steering angle sensor is permanently supplied with power from Terminal 30. This means that steering wheel movements at ”ignition off” are also recorded. The correction value determined during calibration and the steering angle recorded by the potentiometers are still available after power interruptions, but not the number of steering-wheel turns. So that the steering-angle sensor remains able to operate after power interruptions, software has been integrated that uses the wheel speeds or an adjustment of the steering wheel from stop to stop to calculate the number of steering wheel turns. If this does not work on moving off and reaching a speed of approx. 25 km/h, the DSC switches to passive and a fault is entered in the DSC control unit. There is no fault entry in the steering-angle sensor.

In order to further ensure the function, a comparative value is determined continuously both in the DSC and the EDC control units to compensate for deviations in the zero position of the steering-angle sensor. Deviations can result from inaccuracies during calibration, from wear or impacts with the kerb.

Service functions

Steering angle sensor calibration

The zero position of the steering angle is specified during calibration.

Calibration of the steering angle sensor is necessary after the following operations:

• Replacement of the steering column control centre
  
• Reprogramming of the steering column control centre
  
• Adjustment work on the steering-angle geometry
  
• Any work on the steering or front suspension
  
• Replacement of the control unit of the Electronic Damper Control (EDC)
  

The following actions are carried out here in the control units:

• The existing correction value of the steering-angle sensor is deleted.
  
• This leads to entry of the fault ”9501 Steering-angle sensor not calibrated” in the steering column switch centre.
  
• The new correction value of the steering-angle sensor is entered.
  
• The fault code memory in the steering column switch centre is deleted.
  
• The comparative values in the DSC and EDC are reset
  

Calibration is not possible if the vehicle identification number stored on the steering column control centre is not correct.

Coding

The steering angle sensor on the E65 is not coded.