Toyota PRIUS Manual page 279

 Changing "POWER" switch modes
Modes can be changed by pressing the "POWER" switch with the
brake pedal released. (The mode changes each time the switch is
pressed.)
PRIUS PHV_OM_OM47831E_(EE)
2-1. Driving procedures
Off
The emergency flashers can
be used.
ACCESSORY mode
Some electrical components
such as the audio system can
be used.
The "POWER" switch indicator
turns amber.
ON mode
All electrical components can
be used.
The "POWER" switch indicator
turns amber.
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