First, let me say that I searched the threads and found discussion for a similar issue with the Lane Departure Assistant (LDA) in the 2016 model year. I also have the LDA, but that isn't what is acting up. When I first started driving my new Prius November 10 I turned on all the bells and whistles (technology) to see that everything was working. I chose standard sensitivity for those "assistants" with that setting, and drove and watched it all work. Then, this past Monday, on my way home from work, mid afternoon, I suddenly start getting uncommanded inputs to the steering on a four lane roadway. I was using the dynamic radar cruise control at the time, set for 48 mph. I notice the LTA display on the dashboard combination meter has a blinking light blue buffer on either side of the lane. The owner's manual on pg. 316 says this is the steering control indicator and operation display of steering wheel operation support being activated. And these weren't just nudges. It was insistent that I was not centered in my lane and was trying rather strongly to get me there. I fought it for a bit, then pulled over and disabled the LTA. Quick note, there is an on/off key in the lower right steering wheel button line-up for this, the middle key. I went into the combination meter setup pages at the time to find it and turn it off there. Anyway, I figured maybe some spots on the windshield from a little rain was the cause and cleaned the windshield when I got home. Took a quick test drive after that and it appeared to function normally again. Then, early this morning I'm headed back to work, 3:20 am, dark, straight, three lane boulevard, no other traffic. Dashed white lines clearly visible on relatively new road. It starts giving me the jazz again, correcting the vehicle over to the right. Still getting used to the vehicle so that estimate might be off. I was using radar cruise set for 48 mph again. I let go of the wheel and it settled into a track that was maybe 8 inches to the right of center. So I turned it off again and will study my owner's manual and probably visit the dealer about this. This all happened shortly after passing through the 1500 mile mark on the odometer. Maybe that is a magic number for monitoring my driving and now time to suggest improvements? I don't know how many other 2021's are in PriusChat, but maybe someone else has experienced this? I don't think it is a malfunction or an indication of the need for calibration. No warnings came up. I didn't check for codes since I haven't found the OBD-II plug yet. For now, it's a warranty concern. Long post, thanks for listening (reading).
Windscreen clean? RADAR detector (TOYOTA badge) clean? I'm not sure if you have more sensors - they are the primary ones on 2016. What was the weather like - heavy rain (or snow whatever that looks like - we don't have it here, just spiders).
Discovered something important just now. LTA can be turned on without the steering wheel support active, so HAL 9000 (or maybe Alexa) isn't yanking your car around while you're trying to drive. I used the steering wheel button to turn it on coming back with take-out and the dashboard combination meter message said LTA on with steering assist inactive. It drove just fine on the way home. This steering wheel LTA button is nestled between the heated steering wheel switch and the DRCC distance adjustment buttons, so easy to press if you're sufficiently distracted. Back to the owner's manual...
Ah, found it! Page 318. I had the lane centering function enabled. With all these systems turned on it can get very, very close to an autonomous driving experience. Pages and pages of warnings against using the vehicle like that. If you take your hands off the steering wheel there will be a blinking and audible alarm in about 20 seconds.
The more I think about it, this mode should have a new, unofficial name just here in PriusChat. I will call it "DUI Mode". What I've experienced while it is enabled could truly assist an impaired driver, assuming the ideal conditions necessary for its optimum performance. There are 14 pages in the owner's manual about this particular assistant, most pages about when and when not to use it and warnings about what could go wrong. I am saying this obviously with tongue in cheek. The technology though is a step closer to true autonomy.
Thought I would add some more observations I have made in figuring out this system. I'm getting closer to my desired configuration, but there are still some questionable behaviors to figure out and I'm still not completely sure of the configuration of various settings due to the fact that I am driving while all of this is happening. This will pick up where post #4 left off. To review, there are three settings for the Lane Tracing Assist (LTA) in the vehicle settings menu. One that turns on/off the lane centering function, one that turns on/off the steering assist function, and a sensitivity setting that is either standard or high. There is also an LTA on/off button on the steering wheel, lower center button on the right side in between the steering wheel heater switch and the DRCC range button. The LTA lane centering and steering assist selections are linked so that turning either one on or off also turns on or off the other. This is where my problem began, in that I like the lane tracing warnings but not so much the steering assist. I have found that leaving these two functions off and only using the steering wheel LTA button to turn it on or off will provide me with lane departure warnings without the steering assist. There is even a little popup message as mentioned in post #4 that says "steering assist inactive". Sweet.
It's awfully hard to determine if an automated system is working properly without having access to the design documentation. Years ago I rented a car that had "lane keeping" capability. It was basically the same functionality that Lane Tracing / Centering / steering assist provides. I had to turn it off because it's idea about the ideal lane position disagreed with mine. I bought the 2017 Prime with the thought / hope that it would do centering, but did not have the time to read the manual during the test drive so I did not test it fully.
