Toyota Lexusc Owner's Handbook Manual page 79

SWITCHES
Raindrop detection type
"
1 Automatic control adjuster
2 Washer on
To turn the wipers on, move the lever down until you reach
the desired speed setting.
The ignition key must be in the "ON" position.
There are 3 settings:
"AUTO" position — Automatic operation
"LO" position — Low speed operation
"HI" position — High speed operation
60
Automatic operation
The wiper speed is determined by the amount of raindrops
and sunlight detected by the automatic wiper control
sensor.
Twist the automatic control adjuster in the "–" direction to
lower the sensitivity, and the "+" direction to boost the
sensitivity.
The sensor is on the inside of the windshield as shown above.