See also:

Deactivating HDC
Press the button again and the LED goes out. HDC is automatically deactivated above approx. 37 mph/60 km/h. ...

Controls
1 Screen, left 2 Screen, right 3 Controller with buttons 4 CD/DVD player ...

Adjusting volume
Turn knob 1next to the CD/DVD player until the desired volume is obtained. You can also adjust the volume with buttons on the steering wheel. ...