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2016 Dynamic Cruise Malfunction - braking when no cars?

Discussion in 'Gen 4 Prius Main Forum' started by HerbMPG, Jul 15, 2023.

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  1. HerbMPG

    HerbMPG Junior Member

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    Yesterday my cruise control beeped three times and braked but there were no cars in front of me! I reacted by applying the brakes myself to disengage cruise, and slowed down a bit more. This was extremely un-nerving!
    I was driving about 75mph on an interstate while passing a tractor trailer. There was a pickup truck a reasonable distance in front of the big truck. There was nothing in my lane, the road was of very good quality, the lane markers were clear, and everybody stayed in their lanes. Before getting past the big truck, I got the three beeps, but don't remember if the BRAKE! light came on. My Prius automatically braked, and within a second, I applied the brakes as well, mainly to disengage the cruise. But since the car was "prepared," it applied the brakes pretty hard when I applied them. I quickly accellerated back up to speed, but probably not before the car behind me had to slow down.
    Seems like this early version of dynamic cruise is fairly buggy. I've had it disengage before, which is annoying, but not dangerous. It's useful in traffic if you pay close attention. But this new thing has me wondering if I should use it at all! Is there any way to use cruise control WITHOUT the dynamic function? Thanks!
     
    #1 HerbMPG, Jul 15, 2023
  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    If you got beeps and a "BRAKE!" warning then that was the forward collision warning, which would have happened whether cruise control was engaged or not. Fully independent feature.

    Our 2018 Prius c has the same forward collision warning & mitigation system, and very ocassionally does a freakout exactly as you describe- yet our car does not have dynamic radar cruise.

    I feel fortunate that I've only seen it 3 times in 5 years.
     
    #2 Leadfoot J. McCoalroller, Jul 15, 2023
  3. FuelMiser

    FuelMiser Senior Member

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    Yes, when turning CC on, Hold the button down for a few seconds and it will not be dynamic. I'm not sure what the display says, so I would just hold the button depressed until you see something. Or you could crack open the manual and I'm sure it describes what the signal is.
     
    #3 FuelMiser, Jul 16, 2023
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  4. Jburner

    Jburner Member

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    This sounds like something isn’t right. I have the same vehicle with adaptive cruise as well and I’ve never had this happen. Are all of your sensors clear? No bugs and was there sun shining at the sensor at the time? I’ve heard that sometimes setting it off. If you’d rather not use it, just hold down the button long enough for regular cruise to kick in.
     
    #4 Jburner, Jul 16, 2023
  5. FuelMiser

    FuelMiser Senior Member

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    The Pre-Collision System uses both the radar sensor AND the front-facing camera to detect objects in your path and alert you when it's time to brake. So, maybe your front-facing camera is not aligned correctly. If your camera is mis-aligned to the right and you are passing a large semi-tractor/trailer, maybe this will trigger the emergency braking you experienced. Have you had your windshield replaced? Does your lane departure warning still work?
     
    #5 FuelMiser, Jul 16, 2023
  6. HerbMPG

    HerbMPG Junior Member

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    I have had the windshield replaced, but am pretty sure the lane assist has been working properly. I'll double check when I can. Thanks
     
    #6 HerbMPG, Aug 21, 2023
  7. Doug McC

    Doug McC Senior Member

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    I realize this is a rather novel idea on PC, but I will throw it out there anyway: you might want to consult your Owners Manual to see if any of the conditions that it describes for this kind of behavior of the system were met at the time it was happening. Mine actually mentions several.
     
    #7 Doug McC, Aug 24, 2023
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