Trip Odometer Accuracy???

Discussion in 'Prime Fuel Economy & EV Range' started by James Collins, Jun 9, 2019.

  1. James Collins

    James Collins New Member

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    I am new to the Prius Prime, having had a 2016 Prius IV. With the Prius IV with 40,000 miles I was averaging about 55mpg. I was expecting to see the same on the 2019 Prime when not running on the EV battery. In the short time that I have had the Prime, I have made 3 trips between 80 and 100 miles each all with a drained EV battery. Since the car is brand new I was expecting to see something less then 54 mpg on these trips. In general the trips are on fairly level highway driving conditions and the speed varies between 68 mph to 55 mph depending on two or four lane highway. On all three trips the trip meter is reporting between 64 and 65 mpg. The actual milage recorded seems pretty accurate. I am just wonder about the MPG. Is there any way I can check the accuracy of the trip figures?
     
  2. jb in NE

    jb in NE Senior Member

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    Fill the tank before and after each trip.

    For those speeds, the reported mileage isn’t too far off. Perhaps a bit higher than you will get through a measurement.
     
  3. hieronymous

    hieronymous Member

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    In some locations the authorities provide mile marker pegs on a straight stretch of highway for comparison with your odometer. I have found that my PiP, running OEM tires, is extremely accurate, slightly under with new tires and near-exact with some tire wear...
     
  4. bisco

    bisco cookie crumbler

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    are you resetting the trip meter after the wall charge runs out?
     
  5. Salamander_King

    Salamander_King Senior Member

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    My Prime's trip meters report exactly the same mile as ODO (except the 1/10 of a mile in trip meter not reported on the ODO), and ODO meter is dead on accurate comparing to both GPS and hwy mile markers. That being said, on PRIME your mpg of ~65mpg for hwy drive of 55-68mph is perfectly normal. In fact, it is a bit too low IMO. I get ~70 mpg with 65mpg on hwy. Your actual mileage by full tank method calculation will be 5-7% lower than that is being displayed.
     
  6. James Collins

    James Collins New Member

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    Yes the trip meter is set just before starting the trip.
     
  7. Mendel Leisk

    Mendel Leisk Sidewalk Supervisor

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    You're asking if the car's reporting mpg accurately? And how to check the accuracy? Easy: calculate it and compare.

    I get the sense you're also dubious of the odometer accuracy? That I think you can take to the bank: if it wasn't the lawyers would be all over it.

    My 3rd gen's displayed mpg is on average off by 7.5%, always to the "rosy" side.
     
  8. James Collins

    James Collins New Member

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    Thanks, like I said the car is brand new and I expect to see improvements in both MPG and the battery. Can you please extrapolate on why the full tank measure will be 5 to 7% lower. I've always thought the car should know best what milage it is getting, but even on the Prius IV fill ups seem to indicate a lower mpg than the car was reporting.
     
  9. jb in NE

    jb in NE Senior Member

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    It appears the manufacturer has intentionally calibrated this to show a higher mpg than actual. This may be related to test drives at the dealer; the only indicator a potential buyer has is the dash display, so there is a nice incentive to have it show an optimistic number.

    I believe the source of the fuel use data is counting injector pulses and then totalling up the fuel used. There are likely some inaccuracies there, but with as many users reporting the consistent difference between displayed on the dash and calculated from fuel put in the tank, it appears intentionally optimistic.
     
  10. Salamander_King

    Salamander_King Senior Member

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    What I mean is that using full tank method to hand calculate the mpg you will end up with lower mpg than the PRIME display for that duration of trip. I always reset my Trip B to zero when I fill up. And next time when I fill up, I will check the miles on Trip B to calculate miles/gallon. This calculated number is always lower than what is displayed on the car. This has been true for all of PRIUS, and I think all of Toyota cars. If you did hand calculation on your V, as you said the car reported better than true mileage. Of course for PRIME, if you do any of driving with EV mode using charge from the wall, the mpg you get is going to be much higher than gas only HV portion of mileage.
     
  11. bisco

    bisco cookie crumbler

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    you're getting bad mpg reading because it is including the wall charge miles in the calculation. try a trip without any wall charge, and i bet it is much closer to you regular prius mpg.
     
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  12. James Collins

    James Collins New Member

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    Excuse my ignorance, but I do not understand this. First what is wall charge miles?? Secondly, as I previously stated, the EV battery was completely drained and I reset the trip meter just before starting the trip. In the trips I mentioned, they were all return trips and there was no opportunity to charge the EV battery before the return trip.
     
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  13. Salamander_King

    Salamander_King Senior Member

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    Wall charge is electricity you charge from the "wall outlet". Thus enabling EV MODE drive. As you have clarified, you did reset the Trip meter after EV range reached zero. Therefore you are measuring distance and mpg of the HV only using gas for that section of the trip. As I said, Gen4 and PRIME are perfectly capable of getting >65 mpg on conservative drive conditions you have described. So, I don't think there are any errors in your car.
     
  14. jb in NE

    jb in NE Senior Member

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    This appears to be all on gasoline, with no EV input from wall power. So, your actual fuel mileage is (miles traveled on a tank / gals to refill the tank). If you have those numbers and do the math, you will likely see a calculated fuel mileage about 5-7% less than what you were seeing on the dash display. That would be in the range 65/1.07 or a bit less than 61 mpg, which is not unusual under those driving conditions.

    Do the math and the calculated fuel mileage from actual gallons of fuel consumed is your actual mileage.
     
  15. bisco

    bisco cookie crumbler

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    apologies, i thought you were starting with a full charge
     
  16. James Collins

    James Collins New Member

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    No apology needed. I'm just here to learn.
     
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  17. Tideland Prius

    Tideland Prius Moderator of the North
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    50-56mph (80-90km/h) is a pretty good sweet spot for modern engines and transmissions. On a 2014 Corolla with a CVT, I could get 50mpg (roughly.. the instant FE was jumping between 47-53mpg) at 50mph with the cruise control set on a flat road. Naturally, I expect the Prime to get significantly better mpg at those speeds. (You were probably in the 80s.. and that was knocked down by the 65mph stretches).

    But one way to find out is to fill up, do those trips (assuming you do them regularly) and then top up afterwards. Do it a few times to get an average and try to use the same fuel pump at the same station if possible.
     
  18. Elektroingenieur

    Elektroingenieur Senior Member

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    On my 2016 liftback Prius, I never reset trip meter B, and it agrees with the odometer, modulo 10,000 miles, after which the trip meter resets automatically. I’ve previously discussed odometer accuracy, but without a definitive answer; the speedometer adjustment is applied separately.

    Vehicles used by highway departments and others who need extraordinarily accurate measurements are often equipped with a separate distance measuring instrument (DMI), such as those made by JAMAR Technologies or Microdynamics Instrumentation.
     
  19. jb in NE

    jb in NE Senior Member

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    They get their input from the same source, so they should agree exactly. All the trip meters do is apply a reset and subtract a fixed amount from the odometer reading.
     
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