Toyota PRIUS Manual page 634

5-2. Steps to take in an emergency
CAUTION
 If the hybrid system has to be turned off while driving
Power assist for the brakes and steering wheel will be lost, making the brake
pedal harder to depress and the steering wheel heavier to turn. Decelerate
as much as possible before turning off the hybrid system.
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PRIUS PHV_OM_OM47831E_(EE)