Intermittent Collision-avoidance Display?

That's [as clearly explained in the Owner's Manual] the RADAR Cruise telling you that it's switching to RADAR follow:

 

I think the OP is talking about the proximity sensor array which I believe is activated when in D or R and something comes within 12 inches of all sides of the vehicle. The fact that it is activating with no discernable obstructions is an indicator that one or more have been damaged. Should be under warranty still.

 

Yep - I don't have that - pity he/she didn't send a photo.

 

Mine can be triggered by a tall weed near to the car.
The sensor that fired should be in a different color on the display.
If it is not always the same one, you may just have to learn to live with it.

 

This might be what the OP is seeing. And I was wrong, the detection can be as much as 3 feet from the sensor.



Shields Up!

 

That graphic isn't really what it displayed on the dashboard. Those bands are the detection zones. The actual display, a picture of which I can't seem to locate in the user manual, looks like that but the entire zone is one shade of gray. A detection will cause the zone representing the distance to the obstacle to illuminate, and if the detection is in the closest zone it will blink. A buzzer (beeper) sound will also be heard with a repeat rate increasing with obstacle proximity. This system is active in the Intuitive Parking Assist and Parking Support Brake functions, and the Simple Advanced Parking Guidance System. The user manual description and cautions are the place to go, starting on page 362. The cautions mention dirt accumulation or freezing temperatures and frost that may cause false detections.

 

You wouldn't happen to be driving through tall grass or have other foreign materials swirling around the car when these detections occur, would you? The system will detect such things and they will be of a more intermittent nature. It's all mentioned in the Owners Manual

 

IF....you have a sensor going bad, it hopefully will fail completely and fairly soon.
It took the one on my Ford about 6 months to die completely.
My Prius "alarms" going into and coming out of the garage......every time but it stays on long enough to see.

 

are you tailgating anyone in bumper to bumper traffic?

 

I'd be guessing, but maybe it only requires recalibration. Don't know what that might cost. There isn't any distance you can configure it for like the radar cruise control. I get a detection rarely, usually up front on a parking lot bumper or sometimes on the left side when I pull up to a gate kiosk. The distances are less than a foot and I only see the one zone illuminated along with an alarm beep. I do see a display like the one you have photographed when backing out of my carport but only for a second or two and no alarms. It also illuminates the rear zone instead of the front zone, since I am moving in that direction.

 

I've never seen that and the base model LE did not have proximity sensors as standard equipment. Did you upgrade or pay to have blind side monitoring installed?
This does seem to be one or more sensor miscalibration or malfunction. A friend of mine had a bad right front corner sensor on his Tundra. Every-time he parked it or backed out of a parking spot; it would warn that he was about to hit the car parked next to him. He had to take it back to the dealer 3 times before they fixed it correctly. We actually went out and tested it on parked cars - to make sure the dealer didn't simply turn-off the system.
There's also a couple of "eye-site' collision avoidance cameras; located above and behind your rear view mirror. If those cameras are obstructed by dirt or dead insects; you'll also get erroneous warnings. You can't tell if those cameras a blocked; from the driver's seat; It's outside of your field of view. You have to be outside of your car to inspect that. I just noticed your dirty windscreen, in that picture. But this doesn't explain why it would trigger while your backing out of a space - unless your rear cross-traffic sensor is "seeing" something. Again; possible miscalibration.

Hope this helps...

 

I believe the "L Eco" is the base. Le does come with Intelligence clearance Sonar and Intelligence parking assist.

On the crappy roads here in California (although there shouldn't be a reason since this nanny state has the HIGHEST gas prices and gas tax thats supposed to fix the road), some times the Lane Keep Assist thinks I'm "over the line" when its just a line on the road due to a partial repavement.

 

The highlighted item below, is what needs to be recalibrated. FWIW - Clearance Sonar is another name for dynamic radar & intelligent parking assist is another name for rear camera. I don't consider those proximity sensors; those are a totally different and a separate package. I'm speaking about the rear cross-traffic sensors and the blind-spot sensors (shields-up in #6).

Tom, if your windscreen has been replaced - it's possible those sensors behind the glass wasn't recalibrated properly.

• New 2021 Toyota Prius Safety Features
  As a modern hybrid sedan from the Toyota lineup, the all-new 2021 Toyota Prius was designed with the safety and security of the driver in mind and has a standard Star Safety System™ with ten airbags. This model comes offering a host of standard and available safety technologies as well as several driver-assist features that ensure every experience is great and every day as stress-free as possible for drivers in Crystal Lake, IL.
  
  The Toyota Prius comes equipped with technologies like Pre-Collision System with Pedestrian Detection, Full-Speed Range Dynamic Radar Cruise Control and Lane Departure Alert with Steering Assist. For improved driver awareness, the 2021 Toyota Prius features an integrated backup camera and an Intelligent Clearance Sonar with Intelligent Parking Assist, among other features.
  
  • Automatic High Beams
  • Lane Departure Alert with Steering Assist
  • Full-Speed Range Dynamic Radar Cruise Control
  • Pre-Collision System with Pedestrian Detection
  • Lane Tracing Assist
  • Road Sign Assist
  • Adaptive Front-Lighting System and auto-leveling headlights
  • Star Safety System™ and ten airbags

 

In the 2022 Prius OM the system is called Intuitive Parking Assist and is explained in detail. The obstacle detection range can also be changed in the customization settings. Check your OM and see if it is the same for 2021. If you don’t have one you can download one through the Toyota app.
What you are describing is pretty much normal behavior as one of the sensors has an default activation range of close to 5 feet.