Toyota PRIUS Manual page 343

Rain-sensing windshield wipers (if equipped)
The wiper operation is selected by moving the lever as follows.
When "AUTO" is selected, the wipers will operate automatically
when the sensor detects falling rain. The system automatically
adjusts wiper timing in accordance with rain volume and vehicle
speed.
When "AUTO" is selected, the sensor sensitivity can be adjusted
as follows by turning the switch ring:
For Europe
PRIUS PHV_OM_OM47831E_(EE)
2-3. Operating the lights and windshield wipers
Rain-sensing wiper opera-
tion
Low speed wiper operation
High speed wiper operation
Temporary operation
2
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