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Please help me fix naviation error

Discussion in 'Gen 2 Prius Main Forum' started by nicksaadah, Nov 3, 2005.

  1. nicksaadah

    nicksaadah New Member

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    I have noticed that my position marker consistently overshoots roads. That is to say, it thinks I am farther down the road than I really am - the car thinks I am moving faster than I really am! Today, while driving, I went into diagnostic mode and pulled up the sensor display and I noticed that my speed sensor was registering about 2 m.p.h. slower than I was actually going - yes, slower! So, now I'm thoroughly confused - if my car thinks it is going slower than it actually is, I should be undershooting roads, not overshooting them! I have to say, I never noticed this problem until I installed the NAV speed sensor defeat switch - is it possible that the switch I installed is somehow not allong some pulses to go through and fooling the computer into thinking its going slower? I hope someone can help me - thanks in advance.
     
    #1 nicksaadah, Nov 3, 2005
  2. Wayne

    Wayne Active Member

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    #2 Wayne, Nov 3, 2005
  3. nicksaadah

    nicksaadah New Member

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    Hi Wayne,

    Thanks for the reply - actually, I am having this problem when the switch is closed. Ironically, when the NAV defeat switch is open (i.e. speed input to the NAV ECU is inhibited), the car is forced to continuously take GPS states and its position is right on. Unfortunately, the guidance system will not give you voice commands while the switch is open, so I would love a way to correct my velocity bias so I can keep it closed.

    -Nicholas
     
    #3 nicksaadah, Nov 3, 2005
  4. Wayne

    Wayne Active Member

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    Have you tried the two NAV calibrations shown in the NAV manual? They are to calibrate the way the car operates when it doesn't have GPS input, but the same calibration is used to keep your car moving smoothly between GPS updates. Basically it's a current position calibration (you tell it where you are), followed by a tire calibration. It starts on page 77 in my NAV manual.

    Let us know how it turns out.
     
    #4 Wayne, Nov 3, 2005
  5. efusco

    efusco Moderator Emeritus
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    Nicholas, you've done something wrong. Simply disrupting the SS input will not affect voice commands or anything else but the dead-reckoning. I think you may have cut/gotten into the wrong wire or something.

    I suggest you go in and re-solder whatever you cut, or at least take a photo of what your splice looks like/where it is. Did you go behind the dash or under the center console?

    As previously suggested, I think the software override is the superior option anyway (and I'm the one who created the write up for the hardware override).

    Are you aware that the speed sensor manual override only works for about 30-45 seconds before you're locked out again as the GPS detects that you're actually moving? I usually experience lags in the system with the dead-reckoning locked out.

    In any case, the solution here seems obvious to me. Splice your cut wires back together, whatever they are, and just use the software override from now on.
     
    #5 efusco, Nov 3, 2005
  6. nicksaadah

    nicksaadah New Member

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    Hi Dr. Fusco,

    Thanks for the reply - but I'm pretty sure I cut the correct wire (the switch works just as it is supposed to). I think it might be best if I resolder the wire together and remove the switch like you suggest, but I am still confused as to why my speed sensor is registering a slower-than-actual speed? Do you think a faulty switch could cause that?

    What I meant by my voice command comment was that when using the navigation guide to maneuver to a location, if the switch is open, the nice lady no longer gives me verbal directions (they still show up on the screen, but she doesn't tell me what to do)...also, there are a few other issues with the switch open (e.g. if you miss your turn, it won't re-route you if the switch is open). Am I the only one for whom this is occuring?

    BTW, as long as I have you, I wanted to say thank you again for all of your posts to this forum - you are one of the people who is helping us to get the most out of our cars.

    -Nicholas

     
    #6 nicksaadah, Nov 3, 2005
  7. efusco

    efusco Moderator Emeritus
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    Ok, I took it to mean that the voice was totally disabled even with the switch off. To tell you the truth I haven't checked to see if that occurs with mine. I never noticed it, but I don't use it often and always close the circuit before proceeding.

    I don't think I'd sweat the small difference in speed read out. I'm not sure where each signal comes from. The one on the diagnostic screen may be the GPS read speed (which is probably very accurate over a distance, but not so much instantaneously) while the one on your ODO is from your wheel spin rate (or however that is determined). In any case, 2mpg shouldn't have much impact at all on your delay, I would think that would be more of a speed sensor issue.

    That said, do you have oversize wheels/tires? There is a means of calibrating the NAV when you've put on new wheels/tires. It's also possible, even with OEM size, that you need to just go through that calibration. I'm not sure how to do that, it should either be in the NAV manual or you should be able to find it by poking around on the NAV screens.
     
    #7 efusco, Nov 3, 2005
  8. Wayne

    Wayne Active Member

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    I posted a reference above -- calibration starts on page 77 in the NAV manual.
     
    #8 Wayne, Nov 3, 2005
  9. nicksaadah

    nicksaadah New Member

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    Thanks Wayne - I'll try that tonight when I get home and let you know how it turns out.

     
    #9 nicksaadah, Nov 3, 2005
  10. windstrings

    windstrings Certified Prius Breeder

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    1. Does placing the larger tires kill MPG?...
    I think a bit larger tires would look hansome and take the car up higher.. but may kill MPG?

    2. and has anyone tested the tire recalibration to see if MPG is really accurate afterwards?
     
    #10 windstrings, Nov 4, 2005
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