Lexus 2004 GX470 Owner's Manual page 285

AUDIO
Turning the system on and off
Push "ON/SOURCE" button to turn on the rear seat audio
system.
Use "ON/SOURCE" button to select an audio mode when the
rear seat audio system is on. Each time you push this button,
the system changes between the radio, cassette player and
compact disc player.
When you change the mode, the display indicates which mode
is selected.
When a cassette tape and compact discs are not loaded in the
front audio system, only a radio mode can be selected in the
rear seat audio system.
If you push "ON/SOURCE" button on rear seat audio system
controller to select the casette tape player mode or compact
disc player mode in that case, a beep sounds from front audio
system and "INVALID" flashes on the screen for 6 seconds,
and then the rear audio system returns to the radio mode.
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If you push "ON/SOURCE" button while receiving an
emergency broadcast, a beep sounds and "INVALID" appears
on the screen to indicate that no button can be operated.
Push the "OFF" button to turn off the rear audio system.
Finish