CAS stands for the Car Access System. Among other things, two of the main functions of the BMW CAS module include:
CAS module generates random key code every time the vehicle is stared which it synchronizes with the Engine Control Unit, which BMW calls DME or DDE. If you have a defective CAS module, your vehicle may show some of the symptoms below.
For BMW, the CAS module is located under the steering column. To remove the BMW CAS module, you will need to get under the dashboard on the driver side, remove the plastic cover under the dashboard (above the brake and gas pedal). Once you remove the panel, you will find your BMW CAS module, a black or white box.