Toyota Lexusc Owner's Handbook Manual page 317

AUDIO
(a) Turning the system on and off
Push this knob to turn the audio system on and off. Turn
this knob to adjust the volume.
The system turns on in the last mode used.
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Push the "MUTE" button to decrease the volume
momentarily.
To return to its original volume, push the same button again.
When the audio system is turned on, the mute is always off
regardless of the previous mode.