Toyota PRIUS ALPHA 2012 Quick Reference Manual page 292

2-4. Using other driving systems
Selecting conventional constant speed control mode
Constant speed control mode differs from vehicle-to-vehicle distance
control mode. When constant speed mode is selected, your vehicle
will maintain a set speed regardless of whether or not there are other
vehicles in the lane ahead.
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Press the "ON-OFF" button to
activate the cruise control.
Press the button again to deacti-
vate the cruise control.
Switch to constant speed con-
trol mode.
(Push the lever forward and
hold for approximately 1 sec-
ond.)
Cruise control indicator will come
on.
When in constant speed control
mode, to return to vehicle-to-vehi-
cle distance control mode, push
the lever forward again and hold
for approximately 1 second.
After the desired speed has been
set, it is not possible to return to
vehicle-to-vehicle distance con-
trol mode.