Fiat 500 Owner's Handbook Manual page 182

Button Interaction (pressure/rotation)
Deactivate/reactivate the microphone during a phone conversation
Activation/deactivation of the USB source Pause
Activation/deactivation of the radio source Mute function
Short press: volume increase/decrease in single steps
+/–
Long press: volume continuous increase/decrease until released
Short press (Radio mode): selection of next/previous station
Long press (Radio mode): scan higher/lower frequencies until released
Short press (USB mode): selection of previous/next track
Long press (USB mode): fast forward/rewind until released
SRC
select available audio sources: Radio or USB
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