sudden mpg drop

Discussion in 'Prius v Fuel Economy' started by dalenel, Aug 19, 2019.

  1. dalenel

    dalenel Junior Member

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    I drive a 2015 Prius v 5 that faithfully would average 41-43 mpg in the Sierra foothills where we lived. And this included climbing from Sacramento to Placerville on HWY 50 everyday. 6 months ago we moved down the the flatlands outside Sacramento and were happily experiencing an increase to 46 or 48 mpg. 2 months ago I brought my car in for the 85000 mile service at our local dealer and ever since my computer is showing an average of 33 mpg. I took it to another dealer to check it out. They put it on the diagnostic computer to see if it was showing any codes but all was ok. They put an injector cleaner in the gas tank and per their recommendation I switched from Costco gas to Chevron for the last 4 or 5 fill ups. The result of this was no change in the mpg but a much higher gas bill! It does seem to be sluggish when taking off from a full stop. Tire pressure is fine. No new tires recently. I will check out our 12v battery per the advice here but if that checks out ok what should my next step be? If a cell is bad or going bad in the big batteries will that show on the diognotic check? All suggestions are appreciated. Thanks in advance.
     
  2. jb in NE

    jb in NE Senior Member

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    Are all your mpg numbers from the dash display, or have you calculated mpg from tank fill ups (miles traveled divided by gals used)? Did the dealer do any software or ECM updates at the service?
     
  3. dalenel

    dalenel Junior Member

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    Thanks jb
    The mpg is per the dash display. To my knowledge there was not any reset or ecm reset. Nothing to say otherwise on the paperwork. If the big batteries have a cell going bad, will this show on the diagnostic readout? I have used about 1/2 a tank this fill up and am currently reading 33mpg.
     
  4. jb in NE

    jb in NE Senior Member

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    I would measure fuel economy from actual gasoline consumed, which will always be more accurate than the dash display. Mileage will normally vary from tank to tank, even in similar driving conditions. The tank doesn't fill the same level all the time, etc. But the drop you are seeing would get my attention.

    If the HV battery is going bad, this should generate a diagnostic warning.

    Have you checked for a dragging brake?

    What services did the dealer perform at 85K?
     
  5. dalenel

    dalenel Junior Member

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    I totally agree that calculating actual consumption would be more accurate but since I have never done that I'm not sure it would be of any help in this situation since I have no numbers before the service. I don't have my paperwork in front of me to be able to answer what the service entailed. I brought it in with no issues so It was was just the normal service for that interval. Is there a way for me to check for a dragging brake? Thanks so much jb
     
  6. jb in NE

    jb in NE Senior Member

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    There are a few ways to check for a dragging brake. After you drive you car a few miles, stop and put the back of your hand on each wheel. If a brake is dragging, that wheel can be much warmer than the others. You can also use an IR laser temperature measurement device if you have one. Lastly, jack up each corner of the car and spin each wheel.

    My suspicion is that it is not a dragging brake, but it's an easy thing to rule out.
     
  7. dalenel

    dalenel Junior Member

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    Thanks very much for your help. I will do that this evening. And have the 12v checked too.
     
  8. Tim Jones

    Tim Jones Member

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    Oh.....could be the Big Battery.....mine went out and mpg went down before it died...but it wasn't that bad on the mpg.... I get the same 41 / 43 think it was 36.........
     
  9. Firebird-Supra-Prius

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    [QUOTE=" ... my computer is showing an average of 33 mpg.... ok what should my next step be? If a cell is bad or going bad in the big batteries will that show on the diognotic check? All suggestions are appreciated. Thanks in advance.[/QUOTE]

    Sounds like your Traction battery. My 2012 also dropped into the low 30's for MPG when mine failed.
    To Check it - Get an ODB2 Bluetooth adapter and use an app to look at the behavior of each block. There are 14 blocks (each made of 2 battery modules). See if a few are noticeably worse than the others. Or if there is a general failure of the ones in the middle of the pack.
    Torque is popular and detailed, but the quickest and simplest for this is the battery test in the app called Hybrid Assistant .
    A quick test with no setup and it gives you a little graph that makes problem blocks obvious.
     
    Robert Holt likes this.
  10. bisco

    bisco cookie crumbler

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  11. Offline

    Offline Active Member

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    My wife's 2012 Prius v has been averaging about the same fuel economy as the OP is now getting since she retired - about 32 to 33 mph. On most days, she drives her Prius 3.8 miles each way to yoga class in light mid-day traffic mostly on one street with a 45 mph speed limit. Her route is very flat and the few traffic lights are synchronized. She may stop at one traffic light each way but she sails through the other few traffic lights if she drives the speed limit. Very little idling or regenerative braking occurs during her drive and maybe the engine doesn't even get warmed up. Except for her driving to yoga 6 days a week and to a nearby grade school once a week to tutor children for an hour, I chauffeur her around the rest of the time in another vehicle.

    Prior to her retirement, fuel economy was usually averaging 37 to 39 mpg in city driving. I assume that her pre-retirement commute (12.2 miles each way), the stop-and-go rush hour traffic (more than half of which was on an Interstate highway) and hills she encountered were the reason for the better fuel economy. I suppose the traction battery could now be weak after 7 years but the Prius is at only 43,xxx miles.

    FYI, the 2020 RAV4 including the hybrid version showed up on the Toyota website last Wednesday. We were planning to buy a 2020 RAV4 hybrid (we were waiting for the 2020 to get Android Auto) but Toyota threw a wrench in our plan by announcing the 2021 RAV4 plug-in hybrid later last week. I'm currently refueling the Prius v about every 6 weeks. At the rate my wife drives, I would have to refuel a RAV4 plug-in hybrid NEVER unless we were to start using the RAV4 for the highway trips that we don't use the Prius v for. The RAV4 hybrid we test drove a few weeks ago was very pleasant and quiet at 70 mph which I certainly can't say about the Prius v.
     
  12. bostonbruins8703

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    Guess I shouldn't complain. My old commute to work was 550+ miles a week. Mostly highway and using fuelly; I was averaging 49-51 mpg and getting between 490-500 miles on a tank. I had a change in jobs and now I'm averaging 43-47 mpg and around 430-460 miles on a tank. Does highway driving at consistent speeds really have that much of an effect on MPG? My new work route I now drive 256 miles a week. Granted now I fill up even less, instead of once a week, I now fill up once almost every 2 weeks. I watch my gauges like a hawk, I use fuelly for my fill ups. I got new tires a couple months ago, I thought I was past the break in period, but I've only tracked about 2500 miles on my new tires.
     
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