Sound when accelerating the first time after a start

Discussion in 'Gen 4 Prius Technical Discussion' started by Ranko Kohime, Mar 24, 2019.

  1. Ranko Kohime

    Ranko Kohime Member

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    As the title implies, there is a sound when accelerating, around 12-13 miles an hour, ONLY the first time you exceed that speed after starting, and ONLY when it's warm enough that the engine doesn't automatically kick on straight away. (It may happen when it's cold enough that engine does start, but I can't hear it over the engine)

    It's a "sproing", that sounds vaguely similar to a door stop spring. It's not the brake booster, that sound I've come to be very familiar with.

    I'm not worried about the sound, but I'm extremely curious what it is, and what it's doing.
     
  2. CooCooCaChoo

    CooCooCaChoo Active Member

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    We'd need a recording of the sound in order to identify it. The Prius makes a lot of noises, some strange to the first time owner.
     
  3. FuelMiser

    FuelMiser Senior Member

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    Mine has done it since new. I think there's some thread somewhere that addresses it. Try searching...
     
  4. bisco

    bisco cookie crumbler

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    sounds like a sticky suspension bit or brake caliper. i get a good creeping noise every time i back out of my driveway and the car is between the angled driveway and the flat street. happens the first time of the day only.
     
  5. CooCooCaChoo

    CooCooCaChoo Active Member

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    Mine makes a thud when pulling out of my parking spot on first drive in the morning also. I figured it was either suspension related or brake related due to rust overnight. Nothing to be worried about.
     
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  6. Ranko Kohime

    Ranko Kohime Member

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    I made a recording of the sound, hopefully it's clear enough.

    WARNING: I boosted the audio level up, so turn your volume down a bit before listening.

    Sound Clip
     
  7. Ranko Kohime

    Ranko Kohime Member

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    Definitely not rusty rotors, that is a much different sound (though I will say I'm shocked how quickly the rotors develop surface rust on this thing. Overnight in the rain compared to several days in the rain for my other cars)

    It sounds too purposeful of a sound, and too consistent, to be a flaw, it sounds like it's doing something intentionally.
     
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  8. alanclarkeau

    alanclarkeau Senior Member

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    The rotors will look rusty - because you don't use the brakes a lot of the time, so aren't wearing the rust off every time you press the brakes. Don't worry about them, the brakes will last 4, maybe 6 times longer than in a "normal" car.
     
  9. bisco

    bisco cookie crumbler

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    is it the auto door locks?
     
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  10. CooCooCaChoo

    CooCooCaChoo Active Member

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    Yeah, might be auto door locks. Manually lock doors before taking off to see if it eliminates it as a suspect.
     
  11. Ranko Kohime

    Ranko Kohime Member

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    No, those lock when I shift into Drive. This sound occurs around 12-13 MPH, and sounds like it's coming from in front of the left front wheel.
     
  12. bisco

    bisco cookie crumbler

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    not the pedestrian warning system?
     
  13. Ranko Kohime

    Ranko Kohime Member

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    As in a pedestrian warning, or the system doing some kind of startup procedure? I have never seen a pedestrian warning, (peds around here have played Carmageddon and generally know better than to walk out in front of cars :D), and the sound is a bit more mechanical than I would expect from something that should be entirely sensor-based. Unless Toyota has invented some Rube Goldberg type of device. :p
     
  14. bisco

    bisco cookie crumbler

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    it is an electronic kind of whirring sound. if you roll the drivers window down, and drive slowly in ev only inside a garage or similar, you can hear it. the speaker is in front of the drivers side wheel.

    you can also find you tube demonstrations. i believe gen 4 allows you to set volume levels.

    VPNS: vehicle proximity notification system, it should be in your manual.

    there is a thread here on disabling: in the 'gen 4 prius accessories and modifications forum'

    search 'Vehicle Proximity Notification System' by member randomwalk101
     
    #14 bisco, Mar 29, 2019
    Last edited: Mar 29, 2019
  15. Ranko Kohime

    Ranko Kohime Member

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    If my car had that, and unless I missed something I don't believe my Two Eco even has that option, it would long since have been disabled due to the annoyance it would cause me.

    Yes, my hearing is that sensitive, in spite of all the loud music my parents used to complain about when I was younger. :whistle:

    I can say with certainty it's not that, the sound is very different, and also, momentary, (only occurring on acceleration ONCE after the car is started) not sustained like the VPNS.

    The mystery deepens.
     
  16. bisco

    bisco cookie crumbler

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    sounds like two separate sounds in your recording, one right after the other
     
  17. Ranko Kohime

    Ranko Kohime Member

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    Didn't even notice the other sound when I edited. First sound is phone-handling noise, second sound (ends at the 0:02 mark) is what I'm hearing.
     
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  18. GRich

    GRich Junior Member

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    Are you sure it's not the brake test. It makes a single soft squick noise around that speed

    "When the vehicle speed reaches approximately 20 km/h (12 mph), the initial check of the brake actuator assembly is performed and pump motor operation sounds are generated"

    Posted via the PriusChat mobile app.
     
  19. wfolta

    wfolta Active Member

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    I experience something like this and it sounds like a belt slipping once. Sort of like a cross between a chirp and a zipping sound, as if a belt slipped for a moment and then caught. Definitely not a screeching sound like old-school belts truly slipping. Maybe something like a long zip tie being tightened rapidly.
     
    #19 wfolta, Apr 13, 2019
    Last edited: Apr 13, 2019
  20. Elektroingenieur

    Elektroingenieur Senior Member

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    It’s the brake test, as @GRich kindly mentions above; mine does it too, and it sounds just as you describe. The car has no belts, since the air conditioning compressor, water pumps, etc., have to be able to operate when the gasoline engine is stopped.
     
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