Toyota Tacoma 2012 Owner's Manual page 338

3-4. Using the hands-free phone system (for cellular phone)
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Automatic volume adjustment
When vehicle speed is 50 mph (80 km/h) or more, the volume automatically
increases. The volume returns to the previous volume setting when vehicle
speed drops to 43 mph (70 km/h) or less.
■
When using a voice command
For numbers, say a combination of single digits from zero to nine, # (pound),
 (star), and + (plus).
Say a command correctly and clearly.
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Situations that the system may not recognize your voice
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When driving on a rough road
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When driving at high speeds
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When air is blowing out of the vents onto the microphone
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When the air conditioning fan emits a loud noise
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Operations that cannot be performed while driving
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Operating the system with
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Registering a cellular phone to the system
■
Changing the passkey
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