What is a Steering Angle Sensor?
A steering angle sensor (SAS) is part of a vehicle’s Advanced Driver Assistance System (ADAS). ADAS features include a stability control system, emergency braking, and lane-keep assist systems, adaptive cruise control and other safety features. The steering angle sensor connects to the steering shaft and reports either analog or digital data to the vehicle’s stability control system. When the vehicle is aligned, the SAS is calibrated to the straight-ahead position.
Once the vehicle is in motion, the stability control system compares the direction the SAS is showing to the yaw sensor, accelerometer, and lateral sensors. In a skid example, the yaw, accelerometer, lateral, and wheel speed sensors may detect the vehicle moving diagonally while the SAS is showing straight ahead. In that case, the stability control system would assume that the vehicle is in a skid since the driver didn’t move the wheel to cause the movement away from straight ahead. It would then apply the brakes to bring the vehicle back into a straight-ahead position.
When do you calibrate a steering angle sensor?
The SAS sensor must be zero calibrated after an alignment procedure if the toe is adjusted or any change is made to any component that affects the vehicle’s thrust angle. That means you must recalibrate the SAS sensor any time you do a steering or suspension repair that affects toe or thrust angle.
How do you recalibrate the SAS sensor?
Typically, you align the vehicle and then use a professional scan tool to set the zero calibration on the SAS.
How does an SAS sensor work?
As I mentioned above, there are analog and digital versions. Analog sensors receive a 5-volt reference signal and a ground. The third wire reports the change in steering wheel position as the wheel turns a full circle. The voltage varies from 0 to 5 volts during the turn. The stability control tracks note only the change in voltage but also the rate of change to determine how fast the driver is turning the wheel.
A digital SAS sensor uses an optical sensor and an LED to determine degrees of rotation and rate of rotation.
Do SAS sensors fail?
Analog sensors have a higher failure rate than digital sensors, but both can fail
What happens if you don’t calibrate the SAS sensor?
You will get false stability control activation and false ABS braking.
When working on the steering on a vehicle, never turn the wheel when any steering component is disconnected. That will cause the SAS to be miscalibrated.