Eco mode turns off (but light stays on)

Discussion in 'Prius c Fuel Economy' started by Steveandhispriusc, Dec 10, 2017.

  1. Steveandhispriusc

    Steveandhispriusc New Member

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    Hi folks. We have a 2015 Prius c one. 70k miles. Charlotte, NC. Wife drives it 800 miles per week committing to work at mostly highway speeds (65-75 mph). Every day she commutes to the exact same location in Greensboro, NC. The car is always left in eco mode: she doesn't ever press the on/off button for eco mode.

    Until 10-11 months ago, her average gas mileage registered 53.4 mpg consistently. But then we noticed a sharp decline in her average gas mileage to 50.3 mpg.

    With a little at-home testing, I've found that while her eco mode light is always on, the Eco mode function (but not the light) seems to be turning itself off when she turns the car off. So every time she uses the car she has to turn off and then turn on the Eco mode light in order to make sure the car is in eco mode. And I can assure you that my wife doesn't always remember to press off/on the Eco mode light. :)

    Is anyone else noticing this problem? Or had anyone discovered a solution?

    Thanks!
     
  2. wigmann

    wigmann Junior Member

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    I have a 2015 C also and I haven't noticed anything like that. My mileage seems to stay the same in eco mode or normal.
     
  3. Steveandhispriusc

    Steveandhispriusc New Member

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    Thanks for your thoughts. I appreciate.
     
  4. bisco

    bisco cookie crumbler

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    welcome!

    firstly, your gas mileage is fine, and mpg average is down due to the nature of winter and gas formulations. no worries there, everyone's is down this time of year, even in the south.

    secondly, what do you mean by, 'the eco mode light stays on, but the function shuts off'? how can you tell you are in eco mode, other than the light?
     
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  5. Steveandhispriusc

    Steveandhispriusc New Member

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    While winter weather would have an impact, this mileage decrease has happened throughout the summer also. Petrol formulation (increase in ethanol content) could be responsible. That is true.

    When eco mode is on, it is noticeably more sluggish, especially on hills. I tested this by ascending long, steady hills and switching on/off eco mode during the trip up the hill. You can hear the changes in rpm when eco mode is switched off, all other things being constant. I believe there is a noticeable difference in engine output between eco and normal modes.

    Thanks for your thoughts!
     
  6. bisco

    bisco cookie crumbler

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    keep in mind that eco/normal/power modes do nothing but remap the gas pedal so you have to push harder to get the same response, and also effect hvac performance.
    since the purpose is to help drivers improve mpg, it is possible that you are correct, but we have never seen it before.
    a couple things, are you measuring mpg's by manual calculation at the pump and keeping records?
    have you exhausted other posiiblilties that would impair mpg, like tire pressure and etc.?
     
  7. Steveandhispriusc

    Steveandhispriusc New Member

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    Thanks again! The remap of the gas pedal would account for the decrease in rpm while ascending a hill if I don't step harder on the gas pedal. That makes sense.

    My mpg numbers are not based on manual records, but rather on the digital output on the dashboard. That said, we've been measuring mpg from the dashboard since day 1 and resetting Trip B to check changes in mpg over shorter periods of time.

    I've ensured the tires are rotated and inflated to oem specs.

    Great thoughts, sir.
     
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  8. bisco

    bisco cookie crumbler

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    are you keeping up with regular maintenance? oil and filter, air and cabin filters, brake inspections and lubrication, etc, everything in the owners manual?
     
  9. Steveandhispriusc

    Steveandhispriusc New Member

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    Absolutely! I do all the work myself using parts from the Toyota dealership.
     
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  10. bisco

    bisco cookie crumbler

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    the pedal mapping and hvac suppression are computer controlled. if there is a problem, there should be a warning on the dash. with a warning comes a dtc which points toward the ecu or other problem area.
    without these, it in impossible to determine what, if anything, is wrong.
     
  11. Sam Spade

    Sam Spade Senior Member

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    I don't understand. What makes you think that it does not "turn itself back ON" when the car is restarted ??

    Anyway, ECO mode alone won't make that much difference.
    The fact that cold weather is setting in probably has more effect.
     
  12. Sam Spade

    Sam Spade Senior Member

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    And I believe that is wrong. The changes are minor. The gas pedal is "remapped" so that acceleration is slower. The map is also changed for the A/C so that the cooling and fan speed isn't as "aggressive" in ECO.
     
  13. Steveandhispriusc

    Steveandhispriusc New Member

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    Thanks much. No dash lights are indicating an error. It's not pulling any error codes.
     
  14. Sam Spade

    Sam Spade Senior Member

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    Does that mean that it has NEVER been in a dealer's service department ?
    If so, now would be a good time.

    And does that also mean that you passed up their free maintenance for about the first two years ??
    I fail to see the logic in that.
     
  15. Steveandhispriusc

    Steveandhispriusc New Member

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    Thanks. Yes. I believe the pedal remapping would account for the fact that when ascending a hill, if you switch from normal mode to eco mode (and don't depress the accelerator any further) then acceleration would feel more sluggish. I agree completely.

    I'm still trying to determine if/why the Eco mode appears to turn itself off even though the Eco mode light is still on.
     
  16. Steveandhispriusc

    Steveandhispriusc New Member

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    Good point . We used Toyota Care through the first 25k miles
     
  17. dubit

    dubit Active Member

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    I don't know what "C" you drive - but when mine is in ECO mode, it feels like I'm pulling a gravel truck. So I agree with the OP that the difference is indeed noticeable. Don't get me wrong, I use it 95% of the time. But have never gotten used to the sluggish 4 wheeled sled it turns the "C" into.

    But I do agree you when you said in an earlier post that the cold weather setting in would have more of an effect. It's been in the 20's here for the last couple days. It's been cold enough that when I turned off the ECO mode today, the ICE still fired up while sitting at a stop light. Hmm, thinking about that - could this be what the OP is seeing as well? ICE starting up when normally it wouldn't due to cold temps?

    Oh, only turned off the ECO mode today due to a stiff headwind. Couldn't get the car to stay above 50mph without having to get into the "Power" area on my throttle display every 2 minutes. Which is why I say again, the difference is most definitely noticeable between ECO on / ECO off.
     
  18. bisco

    bisco cookie crumbler

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    when the hsi goes into the power band in eco, it is no different than when it doesn't i normal or power. the display is just helping you to try to conserve.

    o/p being in north carolina won't see the hit we are taking weather wise, but some at least.
     
  19. Sam Spade

    Sam Spade Senior Member

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    What EXACTLY makes you think that is happening ??
    So far, you have been pretty vague with details.
     
  20. bisco

    bisco cookie crumbler

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    see post #5.
     
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