CITROEN C4 Aircross 2013 Owner's Handbook Manual page 259

02 STEERING MOUNTED CONTROLS
Increase / reduce audio volume.
Search for a higher / lower radio frequency.
Previous/next CD track.
CD fast forward/back.
Long press: audio system on / off.
Short press: selection of the source in the
following order (in a loop):
CD, SD, USB/iPod, Bluetooth, AUX, FM,
MW, LW.
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