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Dual scangauge anomaly

Discussion in 'Gen 2 Prius Accessories & Modifications' started by Bob64, Dec 17, 2008.

  1. Bob64

    Bob64 Sapphire of the Blue Sky

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    I decided to borrow my friend's scanguage to answer some burning questions... Both sg's have the same version.

    I noticed on a segment of my commute... that the GPH (Gallons per Hour) on the bottom scangauge was stuck on 0.00, no matter how hard I pressed the gas or what the RPM of the engine was... and the TMG (Trip MPG xgauge) under it was going UP, even though the MFD was showing 24mpg.

    Baffled at the strange segment of my commute (it seemed to return to normal after I hit a red light), I decided to check the TMG (Trip MPG xgauge) of the bottom scangauge by comparing it with the top scangauge... and lo and behold:

    [​IMG]


    One of the gauges is... inaccurate. I'm going to have to check again tomorrow to see if this is repeatable, but if this happens to both scangauges... then I'm going to have to take these reported mileage values with a bigger grain of salt then I have been doing...
     
    #1 Bob64, Dec 17, 2008
  2. Neicy

    Neicy Member

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    I have my two daisy chained, and when a value shows in one, it will not display in the other one, or shows zero actually. How did you get one to display twice???
     
    #2 Neicy, Dec 18, 2008
  3. carz89

    carz89 I study nuclear science...

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    I have two SGII's daisy-chained, but normally don't witness what you're witnessing. I've experimented with all the parameters, and can successfully display any parameter on both gages (not showing 0.0). On a couple rare occasions, I did witness the 0.0 on one of the gages for SOC, which I thought quite unusual.

    I think this anomaly may be caused by the signal voltage dropping below a certain threshold on the 2nd scangauge unit. In theory, the two units are actually in parallel, even if it appears that they are daisy-chained in series. So in theory, the voltages at each unit should be identical, but there's probably a minute difference due to line losses in the second cable. I have a short 1-foot cat-5 cable for the second unit.

    However, I have an entirely different problem that I desperately want to fix. I cannot get the two units to read anywhere close to the same MPG reading. When I first bought and installed them, they were reading close to each other, and perhaps only 5-10% off the MFD MPG reading. Then I used them in my other vehicle (Hybrid Highlander) without noticing any discrepancies. While in use in the other vehicle, I entered data into the tank fillup feature before I realized the calibration effect this would have.

    Later on, I returned the two SGIIs to my Prius, and all MPG-hell broke loose, probably due to going through one calibration sequence in my HiHy. After some online research and reading the SGII instruction booklet, I tried to correctly calibrate my two SGIIs. After 4 fillup calibrations, one unit is reading correctly (close to the MFD), yet the other unit remains off by a factor of three to five.

    Looking for some sagely advice on the best plan of attack.
     
    #3 carz89, Dec 18, 2008
  4. TheForce

    TheForce Stop War! Lets Rave! Make Love!

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    I have seen the gauges lock up for a while before. It will eventually start working again after a minute or two. I don't know what causes it or how to fix it.
     
    #4 TheForce, Dec 18, 2008
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