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Significant and Sudden drop in milage (toyota aqua 2012)

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by Oic120, Jun 25, 2017.

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  1. Oic120

    Oic120 Junior Member

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    So I was a happy owner of this 2012 Toyota Aqua (Japanese varient) running the car for more then two years since import and was having a milage around 52mpg (22 km/l) but suddenly something mysterious happened and the milage has now dropped to 35 mpg (15 km/l)
    The only thing I've done is a tire change, stock size was 195/50/R16 and I replaced them with 195/55/R16, but this event had no impact on milage since the car was running fine on these tires.
    I have no issues starting the car, neither have I witnessed any indication that my 12V battery has worn out.
    ODO is 56,000 KM (not miles) and I suppose this is not where I start to think about the HV batteries.
    Since I am in Pakistan, I don't have many qualified Toyota techies available. Googling out the issue is the only way out and I am really looking forward to this forum to help me diagnose this issue.
    So any ideas how can this be diagnosed?
     
    #1 Oic120, Jun 25, 2017
  2. Sean Nelson

    Sean Nelson Active Member

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    A 12V battery problem would probably cause error codes or fail to start the car, I doubt that it would affect gas mileage.

    Is the car going into EV mode at the times you expect? If the hybrid battery overheats the car may stop using it and that could affect gas mileage. The battery can overheat if the cooling vent at the front left of the rear seat gets clogged - that's something that's worth checking.
     
    #2 Sean Nelson, Jun 25, 2017
  3. Robert Holt

    Robert Holt Senior Member

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    You could check the 12-volt voltage in the morning before turning on your Prius at the jump start connection at the rear of the main fuse box under the hood (at least in US models it is a small flip up piece of red plastic with "+" stamped in it.) But causing a 17 mpg drop is huge (6-10 mpg drop is possible with a bad 12-volt). Resting volts should be 12.5 or so, and below 12.0 is a sign of a very weak 12-volt battery.
    Other possibilities:
    IIRC, getting the EGR system clogged could cause an mpg drop of somewhere near this magnitude, but checking the EGR system it is a bit of work, and cleaning the little radiator that cools the exhaust gases is a PITA.
    Does anyone out there have a Techstream system clone, or at least a Scangauge II that you could plug in, program some information request fields, and thus get more relevant info?
    Good luck in any case!
     
    #3 Robert Holt, Jun 25, 2017
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  4. bisco

    bisco cookie crumbler

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    have you owned it since new? any accidents? jack her up and make sure the wheels spin freely. emergency brake is sometimes a cause.
    how many km on the new tires? what brand/model? tyres pressure?
    what the outdoor temp?
     
    #4 bisco, Jun 25, 2017
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  5. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Ok: the only thing you've done is change tires, and yet you dispel the notion that this could be connected to your mpg drop. You would not make a good detective, lol.

    First off: you've changed to a tire with a larger outside diameter, by about 1.7%. So: the car is going to under-report the distance travelled by that amount, and either displayed or calculated mpg will reflect that difference as well.

    Secondly: what tire did you have, and what did you put on? If you've gone from a decent Low Rolling Resistance tire to one that "running fine", but significantly higher Rolling Resistance, the mpg penalty piles on.

    Thirdly: and I'm out of my depth here, but I get the sense if your oversize the tire, isn't that changing the car's "gearing" somehow? Perhaps to the detriment of mpg?? Perhaps the opposite, lol.

    Still, if your accounting is accurate, and your mpg as dropped from 52 to 35, I doubt the tires are responsible for all of it. I also doubt your hybrid battery would be failing so soon, though it's possible, exacerbated by extreme hot climate maybe.

    How long have you been tracking this lower mpg. A month or more? If only a week or so, maybe this is just a short term aberration, brought on by a lot of short trips or whatever?
     
    #5 Mendel Leisk, Jun 25, 2017
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  6. Oic120

    Oic120 Junior Member

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    Thanks for replying. Yes I remember how my car shifted between normal and EV modes, I couldn't observe any difference in the pattern.
    I was thinking about the 12V battery because I read on this forum somewhere that the engine might be busy charging the 12V that's why it's taking up more fuel.
     
    #6 Oic120, Jun 25, 2017
  7. Oic120

    Oic120 Junior Member

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    Thanks for your reply Robert, I'll check the voltage there (that too if the Japanese variant has a jump start connection).
    And can you please tell me whats an EGR system and how is it clogged.
    I pulled off the rear seat in the evening today, and removed the plastic covers (broke those clips too) and checked for any clogging in the HV battery vent, it was as good as new. No clogging no hair fibre no nothing at all.
    And I am not sure if anyone is having these gadgets you just mentioned. Although the local Toyota dealership is offering new Prius, yet all of them are just imported and modified with English language.
    Can you please guide me about this EGR and the gadgets you mentioned? If no one has them, maybe I'll get one for myself if they ain't so costly to import.
     
    #7 Oic120, Jun 25, 2017
  8. Oic120

    Oic120 Junior Member

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    Okay, glad you asked, the stock size was Yokohama 195/50/16 (D variant) and I replaced them with Yokohama 195/55/16 (C Variant)
    And I've bin keeping 30 PSI in all 4.
    The outside temperature is way too hot these days, around 38 - 40°c
    That's a good idea, maybe it's the tires not spinning freely, I'll jack up and see what I get. Never thought of this one.
    And do you think the tire pressure has to do anything here? Keeping equal pressure in all 4?
     
    #8 Oic120, Jun 25, 2017
  9. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    At 50k kms your EGR (Exhaust Gas Recirculation) system is likely fine. Clogging tends to get serious around 150K miles. Just the EGR pipe can be inspected, relatively easily. @NutzAboutBolts has a video on that, pinned at the top of 3rd Gen maintenance sub-forum.

    For tire pressures maybe try raising to to 36 psi, all four, when the car's sat overnight. Not sure what spec is for your stock tire, but likely more than 30 you have set.
     
    #9 Mendel Leisk, Jun 25, 2017
    Last edited: Jun 25, 2017
  10. Oic120

    Oic120 Junior Member

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    You're absolutely rite, tires have a drastic effect on the milage, but once I changed the tires I was very vigilant to see if anything haphazard happens, I kept a record for the milage after the tire change and it was perfectly fine. I think I forgot to mention that after the replacement of tires, my vehicle was running smoothly. And there were no hiccups whatsoever.
    This low milage has been disturbing me since the last two weeks. And when you say extreme hot climate, what does that mean? Because where I live it is around 38-42 Celsius normally.
     
    #10 Oic120, Jun 25, 2017
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  11. Oic120

    Oic120 Junior Member

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    Do you think the car computer (whatever the central CPU is called) should be reset to see if the car gets back to normal?
     
    #11 Oic120, Jun 25, 2017
  12. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Never hurts to try, disconnect the 12 volt meh cable for 30 sec.

    You note mpg drop didn't immediately follow on the heels of new tire install. Understand now. (y)
     
    #12 Mendel Leisk, Jun 25, 2017
  13. Oic120

    Oic120 Junior Member

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    Is it the negative terminal to be removed or the positive one?
     
    #13 Oic120, Jun 25, 2017
  14. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Typo: neg cable is the safest.
     
    #14 Mendel Leisk, Jun 25, 2017
  15. ztanos

    ztanos All-around Geek!

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    Check the vent under the back seat. If it's blocked by anything it can drastically change alter your MPGs.
     
    #15 ztanos, Jun 26, 2017
  16. Oic120

    Oic120 Junior Member

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    Thanks alot guys, you shred some valuable suggestions here, and I couldn't have done it without you.
    So here's what I did and luckily got the milage back to 51 mpg again:
    1. I had these plastic floor mats, at the rear, since they were slightly bigger in size I observed that they are covering the vent intake. Removed the mats altogether.
    2. Reset the computer by disconnecting the negative terminal for ten mins.
    3. The tire pressure was set at 27 Psi, I didn't know what was the recommended pressure but then I found this sticker placed behind the front door that said something in Japanese 220 kpa and 200kpa. Google translate came in handy and turns out this the toyota recommended pressure is 32 psi in front and 30 psi in back.

    So these were some of the things I did and got lucky. Now I don't know which one of them worked but I can sleep better now. Cheers
     
    #16 Oic120, Jun 27, 2017
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  17. Oic120

    Oic120 Junior Member

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    This is what I am getting now.
     

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    #17 Oic120, Jun 27, 2017
  18. ztanos

    ztanos All-around Geek!

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    If I were a betting man, I'd say it was blocking the vent. If you go back to 2013 there were a lot of threads about this exact same issue.
     
    #18 ztanos, Jun 27, 2017
  19. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Try bumping tire pressures a little more, say to around 35 psi. That's by no means excessive, and ride will be still not too harsh.
     
    #19 Mendel Leisk, Jun 27, 2017
  20. Oic120

    Oic120 Junior Member

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    Would it make the milage better?

    Posted via the PriusChat mobile app.
     
    #20 Oic120, Jun 27, 2017
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