ICS Malfunction / Parking Assist Issue

They all do that—at least, Toyota writes in the Repair Manual (more info):

In the following situations, the intelligent clearance sonar system may not operate correctly.
[ . . . ]
(2) Influence from the weather

• When the vehicle is operated under the hot sun or in a freezing climate.
• When foreign matter such as ice, snow or mud is attached to an ultrasonic sensor. If the ultrasonic sensor is cleaned, the system will return to normal.
• It is raining heavily or the sensor is sprayed with water.
• The wind is strong.
• In severe weather such as fog, snow or a sandstorm.

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If you still think there is a problem that could be repaired, I’d suggest going to another dealer or an independent shop that will read the Repair Manual and diagnose the problem using the extensive information it contains about the ICS and IPA systems. Many of the procedures require a Toyota Techstream diagnostic system. The dealer or shop will expect to be paid for this diagnostic service, of course.

I’d start by checking for diagnostic trouble codes (DTCs). This has to be done with Techstream or a true equivalent; inexpensive OBD II code readers made for engine and emissions diagnosis aren’t programmed to communicate with the clearance warning ECU assembly, the computer for ICS and IPA. If if there aren’t any relevant, stored DTCs, I’d also check the Operative/Inoperative Condition History, in Techstream under Body Electrical > Advanced Parking Guidance/ICS/Intuitive P/A > Utility.

There was a campaign for a different ICS problem; for more information, search this thread for “J0R.”