2012 Toyota Prius Owners Manual - Page 532

2 -4 . U sing ot he r driving syst e m s H ill-st a r t a ssist c ont rol Assists with starting off and temporarily maintains braking power even if the foot is removed from the brake pedal when starting off on an incline or a slippery slope. To engage hill-start assist control, further depress the brake pedal when the vehicle is stopped completely. A buzzer will sound once to indicate the system is activated. The slip indicator will also start flashing.