Toyota Prius 2011 Manual page 169

Note for the entry function
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P. 50, 59
Leak detection pump
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Several hours after the engine is turned off, you may hear a sound coming
from underneath the luggage compartment for several minutes. 
This is normal operation and does not indicate a malfunction.
CAUTION
When starting the hybrid system
■
Always start the hybrid system while sitting in the driver's seat. Do not press
the accelerator pedal while starting the hybrid system under any circum-
stances.
Doing so may cause an accident resulting in death or serious injury.
Stopping the hybrid system in an emergency
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If you want to stop the hybrid system in an emergency while driving the vehi-
cle, push and hold the "POWER" switch for more than 3 seconds. 
However, do not touch the "POWER" switch while driving except in an emer-
gency. Turning the hybrid system off while driving will not cause loss of
steering or braking control, but the power assist to these systems will be lost.
This will make it more difficult to steer and brake, so you should pull over
and stop the vehicle as soon as it is safe to do so.
NOTICE
To prevent 12 volt battery discharge
■
Do not leave the "POWER" switch in ACCESSORY or ON mode for long
periods if the hybrid system is not operating.
When starting the hybrid system
■
If the hybrid system becomes difficult to start or stalls frequently, have the 12
volt battery and electronic key battery checked immediately.
2-1. Driving procedures
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