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Had Pre Collision lock up the brakes

Discussion in 'Gen 4 Prius Main Forum' started by Gen 2 Tom, Aug 5, 2016.

  1. Gen 2 Tom

    Gen 2 Tom Active Member

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    I've had two incidences of the pre collision warning alert. It's a beep and a red screen, with I assume a warning message on the center upper screen. No brakes were applied those times.

    Today, I had just accelerated from a light, going about 20 MPH. I don't tailgate and had two to three car lengths between me and the car in front of me. I definitely took my eyes off the road, to observe a good looking woman on the sidewalk. I wasn't on the brakes, and on the gas a bit to roll at 20 MPH. The beeper and red screen went off, and a l/2 second later, before I get to the brakes, the front brakes lock up. Not fully stopping the car before they release. It did all this and I came to a stop with two car lengths it front of me. The guy in front of me did slow down quickly.

    I've had concerns, and still wonder if the PCS works if your on the brakes. I've never had it do anything when I was slowing with the brakes. No mater what the speed. But in all the cases I had the warning or the braking apply, I didn't have my foot on the brake peddle, or I was accelerating as the car in front of me was slowing.

    So It does work!! But will it stop me when I'm rolling with my foot on the brake?
     
    #1 Gen 2 Tom, Aug 5, 2016
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  2. krmcg

    krmcg Lowered Blizzard Pearl Beauty

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    I think your foot on the brake overrides the system.
     
    #2 krmcg, Aug 5, 2016
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  3. Gen 2 Tom

    Gen 2 Tom Active Member

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    I have that feeling as well. We need someone to test this.
     
    #3 Gen 2 Tom, Aug 5, 2016
  4. krmcg

    krmcg Lowered Blizzard Pearl Beauty

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    somebody other than me...
     
    #4 krmcg, Aug 5, 2016
  5. alanclarkeau

    alanclarkeau Senior Member

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    HANDBOOK:

    "If the brake pedal is being depressed, the system may determine that the driver is taking evasive action and possibly delay the operation timing of the pre-crash braking function"

    It also says that if the accelerator is depressed strongly, or steering wheel is being turned, the system may determine that the driver is instead taking evasive action ... and won't intervene.
     
    #5 alanclarkeau, Aug 5, 2016
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  6. Gen 2 Tom

    Gen 2 Tom Active Member

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    Do they really say "if the accelerator is depressed strongly,.......it won't intervene" That must be taken out of context. I think I may have been accelerating when the car in front of me slowed.

    I had distance in front of me and I would have looked back to the road and would have applied the brakes. But the system knew I was on the gas when I should have gone for the brakes. I really liked what the system did in this case.

    What I don't like is the distance the system allows me to get in bumper to bumper traffic. When you need to hold a lot of brake pedal pressure to prevent the electric motor from silently running you into the guy in front of you. There no indication it would prevent this.! I hate this feature that mimics a gas engine car, automatic transmission and the idle speed is set to high.
     
    #6 Gen 2 Tom, Aug 6, 2016
    Last edited: Aug 6, 2016
  7. wrprice

    wrprice Active Member

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    I think (but refuse to test) it looks at the actions you take after or right at the time of the warning. If it says "BRAKE!" and *then* you floor it, you're either exercising extremely poor judgement or taking evasive action. How is the car supposed to know which? If you're Toyota (legal counsel), you trust (defer to) the judgement of the human (person whom will be liable).

    It says if you take braking action after the warning it won't automatically activate the brakes (you just did that) but it will increase the force applied to the brakes at a rate faster than normal braking. This may help make up for some of the lost deceleration opportunity due to any delay in your reaction time.

    The Gen2 would similarly engage an emergency brake assist mode if it detected you stepping on the pedal fast enough and hard enough; with PCS the Gen4 can know it needs to do this before you touch the pedal.
     
    #7 wrprice, Aug 6, 2016
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  8. booke02

    booke02 Active Member

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    Makes perfect sense. The driver has the best view of the situation, so if he is taking some form of active action, he must know what is best. And, ultimately, it is the driver's responsibility.
     
    #8 booke02, Aug 6, 2016
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  9. alanclarkeau

    alanclarkeau Senior Member

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    That was a summary (wasn't in quotes) - here is exactly the words:
    De9dYYYaL2Qa1RCyX4d1SBMC.jpg
     
    #9 alanclarkeau, Aug 6, 2016
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  10. Tideland Prius

    Tideland Prius Moderator of the North
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    This is correct.


    What wrprice is describing in the last paragraph regarding the Gen 2 is called "Brake Assist". This system applies greater brake pressure if it senses that you are performing an emergency stop (you rapidly lift off the accelerator and press firmly on the brake pedal). It will increase the brake pressure if you are not applying enough.

    What the Gen 3 and 4 do with Pre-Collision System is that PCS can prime the brake pads. When PCS is alerting you via the beeping and "BRAKE!" warning message, it is bringing the brake pads closer to the discs to reduce the time it takes for brake application (every millisecond counts). Then it branches off into two options - you react and brake or you don't react and the car automatically brakes.
     
    #10 Tideland Prius, Aug 6, 2016
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  11. Tideland Prius

    Tideland Prius Moderator of the North
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    PCS can help with reaction time as it will begin braking before you react and then you can take over. That crucial second or two makes a difference between missing the car and a fender bender. See video below

     
    #11 Tideland Prius, Aug 7, 2016
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