Replacing Steering-Angle Sensor
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2018 Porsche Cayenne, 2017 Porsche Cayenne, 2016 Porsche Cayenne, 2015 Porsche Cayenne, and 2014 Porsche Cayenne. However, it is still accessible from the selected car via links, so may be relevant.
The steering-angle sensor is integrated in the steering wheel electronics control unit. See → 916255 REPLACING CONTROL UNIT FOR STEERING WHEEL ELECTRONICS