Lexus 2003 LS Owner's Manual page 262

STARTING AND DRIVING
Especially in cold weather, a malfunction warning screen may
appear on the display due to frozen sensors. If the malfunction
warning screen appears on the display, be sure to check the
sensor. If the malfunction warning screen appears despite no
mud, ice or snowflakes on the sensor, the sensor might have
malfunctioned. Have your vehicle checked by your Lexus
dealer.
In the following conditions, the detection range may be
affected:
A When you stop your vehicle in scorching sun or in cold
weather.
A Foreign matter such as snowflakes or mud gets on the
sensor.
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The Lexus park assist system may detect the following by
mistake:
A Bumpy roads or gravelled roads or grass when driving on
such surfaces, or on grass
A Devices issuing ultrasonic waves, such as a horn from
another vehicle, motorcycle engine, air braking sound from
heavy–duty vehicles, if such a device is operated around
your vehicle
A Rain or water splashing over the sensor
A The ground on which the vehicle is tilted
A Radio antenna or fender pole mounted on your vehicle
A Mud, ice or snowflakes on the sensor
A Tall curb stone
A Towing eyelet mounted on your vehicle
A Towing hitch mounted on your vehicle