Mazda 2014 Zoom-Zoom User Manual page 336

Interior Features
Audio System
NOTE
The number of characters which can be
displayed is restricted.
Error Messages
When the message CHECK USB is
displayed, it indicates that there is some
error in the USB device. Verify that the
content recorded in the USB device has
MP3/WMA/AAC files and re-connect
correctly. If the message reappears, have
the unit checked by an Authorized Mazda
Dealer.
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