Calibration of the steering wheel sensor is nothing more than setting the “zero” point in the steering angle sensor. You’re basically telling the SAS where the steering wheel is in a straightforward position.
In today’s article, I’ll guide you through some most common methods to calibrate the SAS.
But before we begin, let’s take a look at how the SAS system works, so you can better understand why, when, and how to calibrate it.
When And Why?
The steering angle sensor serves as a basis for the calculation of various dynamic stability control (DSC) functions. The sensor is integrated into a steering column switch cluster (SZL).
The steering angle indicates the angle position of the steering wheel – 180° to the left and 180° to the right. Every 360° signal is repeated and counted as a full turn.
|3||Electronics (evaluation unit)|
The encoded disc is connected to the steering wheel by the coil spring cassette. When the steering wheel is moved, the encoded disc moves within the optical sensor.
There are different line patterns on the encoded disc for purposes of evaluation.
The optical sensor is built as follows:
- LED and fiber-optical conductor
The LED projects the light onto the encoded disc through the optical conductor.
- Line camera
The line camera converts the optical signals (emitted by the LED) that penetrate the encoded disc into electrical signals.
How it works
Through the optical conductor, light from the LED is projected onto the encoded disc. More or less light will penetrate the encoded disc and reach the line camera depending on the position of the steering wheel. The line camera picks up this optical signal and converts it to an electrical signal.
Signal path: LED → Optical conductor → Encoded disc → Line camera → Analogue signal → Electronic evaluation unit.
Calibration After Disconnecting The Battery
The steering column switch cluster (SZL) is supplied permanently via terminal 30. This allows steering wheel movements to be detected even when the ignition is OFF.
The ZERO position of the steering wheel is retained after a power interruption. However, the steering wheel turn is lost and the steering angle has to be calibrated.
A calculation algorithm re-determines the current steering wheel turn during driving. This means that the calibration will take place while driving.
If this process has not been completed by the time a driving speed of about 20 mph has been reached, the DSC warning light is set.
So, if the calibration was not completed, calibrate the steering wheel position by steering from lock to lock.
Steering Angle Calibration For Active Steering (AFS) Versions
After removing the battery, you’ll need to adjust the steering angle on vehicles with active steering.
Set the steering angle after reconnecting the vehicle battery:
- Start the engine
- Turn the steering wheel left to full lock
- Turn the steering wheel right to full lock
- Turn the steering wheel to a central position
- Turn off the engine
- Turn on ignition (terminal 15)
- AFS warning and Check Control message go out
Note! If the steering rack and tie rods aren’t installed in the “zero” position, you might not be able to calibrate the steering angle sensor. So, if you can turn the steering wheel to one side more than the other, there’s a problem.
When Do You need To Calibrate SAS With A Tool?
The actual steering wheel position is permanently stored in the SZL module as the straight-ahead position during the steering angle calibration.
As a result, when calibrating the steering angle, the front wheels and steering wheel must be exactly straightforward (visual is enough).
The DSC also saves the serial number of the steering column switch cluster as well as the vehicle identification number (DSC allocation to SZL and vehicle). After successful steering angle correction, the fault memory of the steering angle sensor is automatically removed.
A steering angle calibration must always be carried out after the following repair work:
- Replacement of the steering column switch cluster
- Encoding the steering column switch cluster
- Replacement of the DSC control unit
- Adjusting procedure on the steering angle geometry
- Any work on the steering or front axle
How To Calibrate The Steering Angle Sensor
Steering Angle Sensor Calibration With Tool32
Although there are other tools available to calibrate the steering angle sensor, I prefer to use Tool32.
All the software you’ll need for this job you can find here: https://mega.nz/file/T0JyEAbQ#0dCExEqiyQzxPdCswgC9DWwZP77hSicDN9SUXrT4bp4
You’ll also need a K+DCAN cable. You can find a good one here: https://ohptools.com/products/ohp-k-dcan-obd2-usb-cable-interface-for-bmw-e-chassis-models-from-1998-2016
Let’s get started.
Set the wheels in a straight-ahead position as much as possible before running the app.
Connect the power supply unit at the front under the hood terminals. If you don’t have the PSU available, start the engine and keep it running through the process.
Launch the INPA to confirm the connection.
Launch the NCS Expert to find the DSC programming file (SGBD).
Note, or remember the SGBD name. In this case “DSC_89.PRG”,
Launch the Tool32 to calibrate the steering angle.
Load your DCS’s file
In the “Select Job” window find the “lenkwinkel_dcs_abgleichen” and run the job with a double click.
Another window will popup informing you on the job performed. It takes just a few seconds.
Steering Angle Sensor Calibration With ISTA
Besides the Tool32, you can also calibrate the steering angle sensor with ISTA’s service function.
The reason why I prefer to use the Tool32, besides saving 10-15 minutes, I usually need to calibrate the SAS after replacing the SZL module because of repair or retrofit.
The ISTA can not encode the new or used SZL module, so anyways I need to code it with NCS Expert. After the coding, I only need a few seconds to calibrate the SAS.
ISTA Path: Vehicle management → Service functions → Chassis and suspension → Steering angle sensor → Steering angle sensor adjustment.