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cutting the MFD speed wires (not the nav one)

Discussion in 'Gen 2 Prius Audio and Electronics' started by jmann, Feb 26, 2007.

  1. jmann

    jmann Member

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    So, if I understand this correctly, there are two speed wires that go into the MFD that control the "greyout" for audio folders, phone interface and phone book, maintainence screens, and the car moving wheels in the info screen. In addition to these, there is yet another speed wire that controls the nav and nav lockout. Am I right so far?

    All of these wires carry a discrete signal of pulses; presumably with a fixed amplitude, and varying period. Anyone happen to know the waveform properties? it is simply a PWM 5/0 volt signal?

    If the two MFD speed wires are cut, what continues to work and what stops working? Am I correct to understand that the maintainence, phone, and audio work while moving; the info screens report the correct fuel efficiency rates, and trip gas tank millage, but the wheels do not spin and the bar graph does not appear?

    Thanks.
     
    #1 jmann, Feb 26, 2007
  2. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(jmann @ Feb 26 2007, 09:06 PM) [snapback]397026[/snapback]</div>
    Your understanding is accurate.

    Realize that simply cutting the NAV speed sensor wire won't permanantly make access available to the NAV. After 30 sec-1min the signal from the GPS "realizes" that the car actually is moving and again grays out the screen. Otherwise there are not consequences of cutting that wire. But you need the option of turning it off and on to be able to maintain access to the NAV features for a prolonged period.

    You're accurate in the side effects of cutting the bluetooth wire.

    I have no idea what the waveform stuff is.
     
    #2 efusco, Feb 26, 2007
  3. jmann

    jmann Member

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    These are my findings...

    It appears that the Maintainence Grey-out is triggered from the speed on the CAN bus, not the wire because cutting the wire does not affect it.

    However, for everything else, it works like it is supposed to.

    The wire apparently carries a square wave signal between 0.1V and VCC-0.1 V (about 13.8V). It appears one period is slightly grater than the inverse of speed (in MPH) such that, for example, 10MPH<~>11Hz. If you drive slow enough, you can see the square wave change states, which indicated that this is the direct output, and you can stop with the wave at either polarity. So, this is coming directly from a rodery encoder on the drive shaft. I do not know the duty cycle of the wave

    I will provide more updates as I go.
     
    #3 jmann, Mar 25, 2007
  4. Zanti3

    Zanti3 New Member

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    I was doing my own research on this very recently and found the following Web site.

    http://evnut.com/prius_speed_wire.htm

    The site does a nice job of explaining what functions get disabled when you cut the wires and even has color pictures to guide you through the process.


    OK, I've gotten the nerve up to try making this "customization". From what I have read, it sounds like the easiest way to get to the speed wire is through the vent panel that is immediately to the right of the MFD and the radio. For anyone who has done this, I have a few dumb questions. (I don't want to ruin anything expensive, of course.)


    (1) The vent panel should unsnap, correct?

    (2) Did you pry it off from the top?

    (3) Did you have to apply a lot of force, or should it pry off fairly easily?
     
    #4 Zanti3, Apr 17, 2007
  5. lesturner

    lesturner Taming the Dragon - Tennessee

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    The vents tend to come straight forward. They take a bit of pressure to get off but are simply snapped into place. A flat-blade screwdriver with some electrical tape around the end (to keep from scratching the surface) makes a great little prybar.

    The wires are fairly easy to find and connect to. I simply ran them to a DPDT switch in the lower console (where the cig lighter jack is).

    Only things that it 'adversely effects' are the bar graph disappears, the GPS is slow to respond, and the animated wheels stop turning. I generally turn the switch off while I need access to the controls and back on when done.
     
    #5 lesturner, Mar 12, 2008
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