Toyota 2013 Prius Owner's Manual page 362

2-4. Using other driving systems
Disabling pre-collision braking
Radar sensor
336
PRIUS PHV_OM_OM47787U_(U)
Pre-collision braking enabled
Pre-collision braking disabled
The "PCS" warning light will
turn on when pre-collision
braking is disabled.
The radar sensor detects vehi-
cles or other obstacles on or
near the road ahead and deter-
mines whether a collision is
imminent based on the position,
speed, and heading of the obsta-
cles.