Steering Angle Sensor Diagnosis and Repair
The steering angle sensor (SAS) is the way by which a vehicle’s computers monitor the position of the steering wheel. Such a position measurement is used by the stability and control system to infer what directional response the driver desires from the vehicle. The steering angle sensor provides critical and high-frequency data for the vehicle stability control (VSC) and ABS.
The experts at Hollenshade’s in Towson can address any problems you may experience with steering or other electronic vehicle sensors. Please contact us for an appointment or to ask us a question about a steering and suspension issue or repair for your vehicle.
Understanding the Data
It is critical that an array of different computer modules and systems receive an uninterrupted signal from the steering angle sensor. The angle of the steering on its own can be used to determine where the front wheels are pointed. The steering angle position data is used in conjunction with pieces of information from other sensors such as the yaw rate sensor, lateral G-force sensor, wheel speed sensors, and other accelerometers by the vehicle’s on-board computers. These pieces of information are used to formulate a snapshot-in-time of the dynamic condition of the vehicle. This calculation is performed over and over again by the computers, at a high-frequency rate, usually measured in kHz.
How the Data is Used
Vehicle computers observe changes in the data over time and make inferences about the driver’s intentions. Acceleration in these data channels, also referred to as the rate of change, provides feedback to the computers for evaluation of the vehicle’s reaction, available performance based on road conditions, as well as the perceived level of performance by the driver. Such an approach is the foundation of modern-era stability control systems. The steering angle sensor data PID can be used for other vehicle systems including electronic power steering, intelligent headlights, and even automatic stop/start systems.
Sensors and Calibration
Many vehicles require the SAS to be reset or re-calibrated after an alignment is performed or parts in the steering system are replaced. There are three different types of reset procedures: scan tool, Self-calibrating, and manual methods that usually involve the jumping of wires/pins in a specific electrical connector. Most vehicles can tell if traveling in a straight line. Thus, if the computer determines the SAS is out of calibration it will disable the electronic steering control (if equipped) or power assist. Some newer vehicles can auto-calibrate by having the steering wheel turned from lock-to-lock and then cycling the ignition key with the wheel straight-ahead. Such procedures are always performed on a straight and level roadway or surface.
In most cases one sensor would be fine. There is only one crankshaft position sensor, one wheel speed sensor per wheel, and one output speed sensor on the transmission. However, steering angle has become such a cornerstone measurement for vehicle systems that redundancy has been designed into the steering angle sensor. The steering angle sensor usually has two or three sensors packaged into the assembly. Other components with a similar design are the throttle angle sensor and gas pedal used for vehicles equipped with throttle-by-wire. Why multiple measurements.. recall the ‘runaway Prius’ issue years ago?!? Such a design approach also provides for additional accuracy and diagnostic abilities. The two signal outputs are checked against each other. Most vehicles produce a positive (+) voltage turning right and a negative (-) voltage turning left.