Steering Angle Sensor Operations

Steering Angle Sensor Operations

It is important for the ABS/ESC module to receive two signals to verify the steering wheel’s position.

Measuring the steering wheel position angle, rate of turn and torque applied by the driver are typically the job of a sensor cluster that contains multiple steering angle sensors (SAS).

The sensor cluster will always have more than one steering angle sensor. Some sensor clusters have three sensors for redundancy, for improving the resolution of the sensor cluster and to confirm the data. It is important for the ABS/ESC module to receive two signals to verify the steering wheel’s position. These signals are often out of phase with each other.  

Analog SASs are similar to throttle position sensors. SASs are wired with a 5-volt reference, chassis ground and signal output. To test the SAS, you have to backprobe a connector that is typically under the steering column. 

As the steering wheel is turned, the SAS produces a signal that toggles between 0 and 5 volts as the wheel is turned 360 degrees. As the wheel is turned lock-to-lock, the voltage will reach 5 volts three times and 0 volts three times.

On most vehicles, turning to the right creates a positive voltage and to the left generates a negative voltage. But, some systems are the opposite. The labscope pattern shows the signal traces from the two sensors on top of each other. This can be helpful when comparing the signals and if one is flat lining.

A digital SAS is often called a “contactless sensor.” This type of sensor uses an LED light, a wheel that acts as a shutter and an optical sensor that measures interruption in the light. The signal for these types of sensors is a digital square-wave signal. The frequency of the voltage changes depending on the speed the wheel is turning.

The sensor clusters for these sensors often contain a third sensor to measure if the wheel is centered. With the wheel straight, the voltage is close to 0 volts. When the steering wheel is moved off center, the voltage goes high.

Some scan tools will display the data as an angle. In some cases, you can see the voltages from the sensors.

Torque Sensor

Measuring the amount of force being applied by the driver to the steering wheel is used by both the stability control and power steering systems. The information can be used to determine driver intentions and the performance of the power steering system. But, it can also detect a steering pull.

The torque sensor performs the same function as the torsion bar and spool valve in a hydraulic system. The electronic sensor uses a torsion sensor in the same manner as in the spool valve in a hydraulic power steering system. There are different types of electronic torque sensors, and they are classified as contact and non-contact types.

Steering Sensor Clusters

Most vehicles mount the steering angle and torque sensors in a single module on the steering shaft. Some call it a steering sensor cluster. The module connects to a Controller Area Network (CAN) bus. On some vehicles, it can connect directly to the ABS/ESC module. 

Resetting Sensors

Many vehicles require the SAS to be reset or recalibrated after an alignment is performed (even if the rear toe is adjusted) or components in the steering system are replaced. There are three types of reset procedures:

  • First, systems that self-calibrate on their own. 
  • Second, vehicles that require specific wires to be grounded or buttons be pressed. 
  • Third, systems that require recalibration with a scan tool. 

Even if the SAS is out of calibration, most vehicles have ways to sense if it is traveling in a straight line. If the angle is far enough out of range, it might set a trouble code and disable the ABS and/or ESC system.

Self-Calibration

On some import vehicles, recalibrating the sensor after an alignment or if the battery has died is just a matter of turning the wheels lock to lock, centering the wheel and cycling the key. This “auto learn” functionality is becoming more common on newer vehicles.

Scan Tool Steering Angle Sensor Reset 

There are many options for scan tools to reset steering angle and torque sensors. Some tools are even integrated into an alignment system. But, most tools recommend that the calibration be performed on a level surface. This is because you are also calibrating the yaw and accelerometers. 

Also, it is always a good idea to perform a lock-to-lock steering wheel turn to complete the calibration.

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