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ScanGaugeE reports slightly less miles than the MFD ???

Discussion in 'Gen 3 Prius Technical Discussion' started by szgabor, Jun 30, 2011.

  1. szgabor

    szgabor Active Member

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    I just got this ScanGauge E device. After a couple of weeks of use I started notice that the miles reported by the OBDI reader is lower than the MFD !!!!

    What I do is to restart Trip A at fill up similarly the ScanGauge use the Fillup function.

    Then I noticed that the scanner has slightly fewer miles than the MFD and the diff is growing as I go ...

    Anyone ever noticed this ?? How can the scanner get different numbers ??

    For example, right now the MFD shows 148.7 the scanner shows 144 this is sligthly over 3%

    I will start taking notes to see if there is a the trend ...

    This very well could account for the the 4-6% MPG difference.

    Still puzzled but if I accept the scanner result then the car cheats me out of warranty among other thing...

    If this could be Scangauge error then how can we trust any other numbers it reports.


    Any idea ???
     
    #1 szgabor, Jun 30, 2011
  2. spiderman

    spiderman wretched

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    I am surprised that the actual distance is off. That should be dead on. I think others here have check with GPS units and found the distance to be accurate.

    I will have to set my SG up to measure distance and see what I get.
     
    #2 spiderman, Jun 30, 2011
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  3. Teakwood

    Teakwood Member

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    Oh my. Minor inaccuracy that would be expected on an analog gauge, now reported on a digital gauge.
    Oh, the humanity! End of the world. Panic-panic.
     
    #3 Teakwood, Jun 30, 2011
  4. szgabor

    szgabor Active Member

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    What are you saying ??? What analog gauge? You think the Prius has some cable based odometer ?

    Again I am not yet sure if this is real or human error or some odd thing with the ScanGaugeE .. I am taking notes on paper to see.

    I have a GPS but do not use it daily ... (not even in the car)... if this difference stays or increases I will try to verify it with the GPS ...

    Cheers
     
    #4 szgabor, Jun 30, 2011
  5. fuzzy1

    fuzzy1 Senior Member

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    Right now mine is the opposite: 577.5 on the MFD, 580 on my ScanGauge-II, for an error of about 0.4% low. Not high like yours.

    I already know from another source that my MFD was reading about 0.2% low last fall, with these same (but slightly less worn) tires.
    Toyota would be engaging in idiocy if they were cheating you after Honda and Subaru settled odometer-error class action lawsuits by extending their warranties 2%.
     
    #5 fuzzy1, Jun 30, 2011
  6. szgabor

    szgabor Active Member

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    Not sure what is happening, but I know for sure this is not my imagination the difference is growing ....

    Now the scangauge-e gives only full mile and the MFD one decimal so there is some error there but see the table (I am using the median of the possible reading to calculate the %)...

    I took reading after four trips go and return to/from work four identical routes (but back and forth so terrain is cancelled out ).

    Column 1 Column 2 Column 3 Column 4 Column 5
    0 SG-E MFD Diff (-/+) Mid -%-
    1 165 170.4 4.4/5.4 4.9 2.8
    2 187 192.8 4.8/5.8 5.3 2.6
    3 210 216.1 5.1/6.1 5.6 2.6
    4 232 239.5 6.5/7.5 7 3.0


    Next week will use GPS to see which one it agrees with.

    Anyone else with ScanGauge-E care to comment ??

    In the meantime will contact manufacturer....
     
    #6 szgabor, Jul 1, 2011
  7. alfon

    alfon Senior Member

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    I checked my odometer with the 5 mile measured markers
    on Interstate 5 near Olympia Washington and found the Odometer to be just a hair off.

    For instance at 5 miles the odometer would read a hair less. So in 100 miles the odometer may read 99.5 or so.

    Also the speedometer is off a little. If it reads 35 mph on the guage actual radar speed is about 34 mph.

    Alfon
     
    #7 alfon, Jul 2, 2011
  8. fuzzy1

    fuzzy1 Senior Member

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    Outside GPS, my best odometer check was against the I-90 mileposts between the Columbia River and the Idaho border, about 160 miles. While a few posts were a bit out of place, the pattern was fairly consistent except for a big discontinuity in the vicinity of mileposts 220 and 221 near Ritzville.
     
    #8 fuzzy1, Jul 2, 2011
  9. szgabor

    szgabor Active Member

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    Here what ScanGauge (the manufacturerer) suggest:

    "Hello Gabor,

    Thank you for your inquiry. I spoke to our engineer regarding your email and he suggested that you set the update rate on your ScanGaugeE to FAST (page 16 of user manual). This should help smooth out the distance reading. Also, try and check the MPH reading on the SGE compared to a GPS if possible. The ECU might be off a few MPH, so the SGE will need to be calibrated to compensate for this. Please refer to page 17 of the user manual for instructions on how to adjust the speed on your ScanGaugeII. Please let us know if you have any further questions.


    Regards,"


    Anyone care to comment ???

    I am not sure how MPH difference relates to the possible difference in distance (SG calculates backwards ???)

    Anyway will try to do what they suggest ... my GPS can not (or I can not figure how to) show distance easily, but seems to report MPH just fine ..

    Short observation SG shows about 1 MPH less (consistently 1 less when I go steady speed).

    When there is a sudden speed change it is either equal or 2 less this probably some sampling delay ... but again MFD show +1 MPH ... so I will use my GPS to see.

    But there are many report that Prius 2010 DOES over report speed (as most car !!!)

    I have many of those radar controlled signs on my way to work, and I already noticed that MFD was showing the same 1 MPH (plus) error ...
     
    #9 szgabor, Jul 5, 2011
  10. szgabor

    szgabor Active Member

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    Update ....

    Finally I got a lot faster (and hopefully more accurate) GPS.

    I tested the car speedomoter and the now adjusted speed on the ScanGaugeE ...

    The car is very very close to the GPS. It is harder to tell in variable speed because the car changes much faster but at steady speed they match at the most 1 less on the GPS but mostly the same....

    So it makes me wonder how Scangauge works and what it reads from the car computer ... it seems it calculates the distance from speed and time, so adjusting the scanner speed reading to match the car makes the distance very very close as opposed to the 3.5-4% difference it is well within 0.5% ... it was less than 1 mile difference on a 529 miles tank....

    And for the curious the scan's reading is much closer to the calculated MPG over a tank, than the car but still about 1-2% off so far always higher. So maybe the sensor(s) have a systematic bias ....

    Also using the scanner helped improve my driving and MPG (although I am driving a prius for over 4 years first a 2nd generation and now a 3rd...)

    Seeing RPM is a huge help to adjust driving some of the other gauge(s) are useful as well like temp and load
     
    #10 szgabor, Aug 16, 2011
  11. jdcollins5

    jdcollins5 Senior Member

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    The speedometer display on the Prius is about 2 mph high at 60 mph. This is due to some UN mandate. There are several threads on here that addresses this.

    If I am running 60 mph on the speedometer my ScanGauge II displays 58 mph. Others have stated that the Prius computers know the true speed of the car and the internal calculations are correct.

    I have not adjusted the MPH on my ScanGauge II to make up for this difference since I know about the difference and know that the ScanGauge is reporting the true MPH. From what I remember the Tank Trip mileage is pretty close to the MFD. I will have to pay closer attention the next time I fill up.
     
    #11 jdcollins5, Aug 16, 2011
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  12. fuzzy1

    fuzzy1 Senior Member

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    ScanGauge's MPG readout will be however accurate you calibrate it to be.

    At least for my old OBDII-bussed car, it has no direct access to fuel consumption. It does have access to air mass flow information (engine displacement provided by user, RPM, intake manifold air pressure and possibly temperature) which, combined with a known fixed fuel:air ratio, can be used to estimate fuel consumption. Because it cannot accurately compute everything -- for example, it doesn't have information to distinguish between E10 and pure gas, or the different energy densities of summer and winter fuel blends -- it depends on feedback at the fuel pump to get dialed in accurately.
     
    #12 fuzzy1, Aug 17, 2011
  13. fuzzy1

    fuzzy1 Senior Member

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    That UN mandate applies only to certain Eastern Hemisphere markets such as the EU. None of its listed countries is in North or South America.

    In the U.S., the speedometer offset is driven by some state laws, and is smaller than typical offsets in EU markets.
     
    #13 fuzzy1, Aug 17, 2011
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  14. szgabor

    szgabor Active Member

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    Not sure what you are saying my MFD reads pretty much what the GPS says less than a MPH difference at speeds around 60 MPH(like 50-65)

    The ScanGauge was lower ... and before I adjusted it, the miles reported (by day or tank or current) was off 3-4% !!


    The car CAN NOT know it's speed unless it relies on some GPS device which as far as I can tell the prius doesn't have by default !!!

    If I am wrong I am sure someone will correct me. The car relies on the specs (as long as you use the correct tire and it is in reasonable wear on it ) the speed and distance will be within certain error... this is why I was suprised that ScanGauge was reporting something wierd ...I guess it calculates stuff from the data !!!

    Cheers
     
    #14 szgabor, Aug 29, 2011
  15. jdcollins5

    jdcollins5 Senior Member

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    The car knows the speed of each individual wheel through sensors on each wheel. It uses this in the ABS system to know when a wheel is slipping.

    It uses these speed sensors for car speed. Of course, as you stated, this will depend on using the correct tire size. If the tire size changes from original spec, then the speed indication will be off.

    If you will search on here for Speedometer Error you will find several threads concerning the difference in MPH on the MFD versus true car speed. The speed on the MFD is artifically high by a certain percentage as set by state laws.

    My ScanGauge reports the true car speed which is different than the MFD display. My ScanGauge indicates 58 mph when the MFD indicates 60 MPH. This agrees with most others on here in other threads.

    Hope this helps.
     
    #15 jdcollins5, Aug 29, 2011
  16. szgabor

    szgabor Active Member

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    OK, we kind of saying the same thing the car can only measure certain things like wheel rotation/speed but what I am saying this is not really the car speed (under inflated tire, option wheels etc). And of course for the ABS this doesn't really matter.

    I thought the best way to check the real speed versus
    reported (speedometer/MFD) speed is using a GPS ...

    And more traditional stopwatch and mile markers :)

    (certainly not ScanGauge because that is also getting the the data from the car computer whatever that algorithm is) and I am now convinced that it calculates distance based on reported speed ....

    Now, I am trusting the the TomTom GPS for the speed which is very close to the MFD my tires are the factory ones and sofar not too worned and I am keeping a close eye on the pressure as well. I can not imagine that GPS will also "over" report speed :)

    And also checked against google map to confirm distance of a few route(s). In other words I do NOT see much speed (MPH) errors and after adjusting the scangauge as suggested by the manual it reports route distance as expected ....

    Anyway, just wanted to document what I did and found with this new ScanGaugeE.

    Cheers,
     
    #16 szgabor, Aug 30, 2011
  17. qbee42

    qbee42 My other car is a boat

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    The email from ScanGauge suggests that the ScanGaugeE device calculates mileage from speed and time. This means that ScanGauge mileage is subject to errors from the Prius speedometer, and must therefor be calibrated to remove these errors.

    The internal odometer of the Prius, on the other hand, is fixed to wheel rotation and cannot be calibrated.

    Tom
     
    #17 qbee42, Sep 1, 2011
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  18. szgabor

    szgabor Active Member

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    Thanks for your comment,

    I concluded the same myself ... except the scangauge reads some data and even calculates the MPH it shows... and that can be calibrated....

    Someone wrote that the MFD speed is higher by 2 then the "real speed"... I actually did not find that at all compared to my GPS.

    And the odometer seems pretty accurate as well reports almost exactly the same as the GPS trip distance and/or known routes I am driving by google maps....

    Again I think tire wear or none factory wheel size will surely change that .... :)
     
    #18 szgabor, Sep 1, 2011
  19. xs650

    xs650 Senior Member

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    You or I can't calibrate it, but it can be calibrated. It counts pulses from something that turns with the wheel, then does a calculation to turn those pulses into miles. It's just amatter of finding the constants used in that calculation and changing them.
     
    #19 xs650, Sep 1, 2011
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  20. qbee42

    qbee42 My other car is a boat

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    It's designed to be tamper resistant, for the same reason that mechanical odometers are protected against rollback.

    Obviously you can insert a rate converter into the pulse stream if you really feel the need.

    Tom
     
    #20 qbee42, Sep 1, 2011
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