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2006 Prius: Sudden dramatic drop in mpg caused by battery problem?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by lyvisky, Sep 14, 2014.

  1. lyvisky

    lyvisky Junior Member

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    We bought our 2006 Prius new in Tallahassee Florida. We love it!!!! It now has 109,000 miles. We've had all scheduled maintenance performed and oil changed every 3500. We've used mainly regular CostCo gas (up to 10% ethanol) with occasional non-ethynol that gives marginally improved mpg--seemingly not worth extra price. Only OEM replacement was aux battery at about 50,000. A month ago, after being parked in the sun for two hours on a 97+ degree August day, startup was difficult and engine hesitated repeatedly. We suspected "vapor lock". Toyota certified mechanic performed full tuneup including new OEM spark plugs. Per advice found on PC, we added a heat shield to the back deck to reduce heat in the battery compartment. MPG, which had dropped from mid-40's to low 30's, (and sub-20 uphill!) did not improve after tuneup. I have noticed that stopped at a traffic light, the fuel efficiency bar graph, which usually lights up to the top (100 mpg), now sometimes stays at the bottom. In case it's "bad gas", I plan to fill up with non-ethynol when fuel tank gauge shows one bar. What could cause this? Could it mean my big batteries are dying? Thanks!!

    P.S. I gave my 6'3" husband a birthday surprise of the "Extend-My-Seat" extensions on both front seats, purchased through the PriusChat store. He is ecstatic with this newfound comfort and is now willing to go for 300,000. Just sorry we didn't know about them sooner! Also added NavScreen sun shield--great!
     
    #1 lyvisky, Sep 14, 2014
  2. Easy Rider 2

    Easy Rider 2 Senior Member

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    Could be.

    When the shop had it for a "tuneup", did you tell them what your complaint was ?
    If not, you should give them another shot at it and pray that they are competent.

    It could be the 12 V battery again and the "standard" test might not show it bad.
     
    #2 Easy Rider 2, Sep 14, 2014
  3. drmanny3

    drmanny3 Member

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    I doubt your problem is gas related. And I would be surprised that it is the 12 volt accessory battery. Have you recently changed tires in the front or did you by chance run into a pot hole? Check to make sure your alignment is ok. Look at the front treads and make sure they are wearing evenly. At a stop my mileage goes from 100 as I coast to zero as I sit at a light. So I think it is something else. If not tire or brake related it might be electronics. Your traction battery is what gives a hybrid the ability to skimp on fuel. There could be something going on either with it or the electronics. I think a Toyota Technician is the way to go.
     
    #3 drmanny3, Sep 14, 2014
  4. wjtracy

    wjtracy Senior Member

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    It's not the fuel, although you might see 3 to 10% better MPG with E0.
    Quite a few 2006's (maybe around 5% now) have had to replace the hybrid battery as they get to your (and my) car's age.
    Probably it's a higher % in hotter places like FL.

    You can try to be kind and gentle on it by warming up car a few minutes before you take off. The engine comes on and charges the batt a little and then the engine goes off. This brings the hybrid system to the next stage where the hybrid battery use is less aggressive.

    Parking in the hot sun can be a problem in some rare cases like if the battery is all charged green and you park in the heat the battery can overheat.
     
    #4 wjtracy, Sep 14, 2014
  5. nh7o

    nh7o Off grid since 1980

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    Tallahassee would count as a hot climate for much of the year. The statistic that has come across here shows HV battery life is shorter in hot places. As mentioned, parking in the sun is to be avoided. If the battery is showing green bars, let the A/C run while in park until the bars drop down to blue before leaving the car. Reflectors in the windows are very much needed.
     
    #5 nh7o, Sep 14, 2014
  6. lyvisky

    lyvisky Junior Member

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    Thanks to everyone for all the comments and suggestions! In my original post I mistakenly stated that I thought the mpg column should stay at 100 at a stop. Actually, the variance from what I consider "normal" is that when I take my foot off the accelerator, the mpg column, which should shoot up to 100, now occasionally stays in a low mpg range. I have 4 relatively new tires, and no pothole incidents. We are considering a visit 275 mile trip to Tampa Hybrids for battery load testing and possible grid recharge and balance (or exchange). I'm sure the $190 tuneup didn't hurt but was wrong "why". Any further comments about this angle?
     
    #6 lyvisky, Sep 18, 2014
  7. JC91006

    JC91006 Senior Member

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    Try a good cleaning of your throttle body and maf sensor. Change the air filter if it's dirty. Check your oil and coolant level to make sure it's not low.

    Engine hesitation can come from bad coils and injectors as well, but that would normally trigger a code
     
    #7 JC91006, Sep 18, 2014
  8. lyvisky

    lyvisky Junior Member

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    Thanks, JC91006! Todd at Tampa Hybrids checked the batteries (good!), cleaned the throttle body, serviced the transmission, and cleaned the battery compartment fan. MPG went from mid-30's to high 40's overnight! Thanks, Todd!
     
    #8 lyvisky, Oct 3, 2014
    Mean Kitty likes this.
  9. bisco

    bisco cookie crumbler

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    congrats!(y)
     
    #9 bisco, Oct 3, 2014
  10. paulcummings55

    paulcummings55 Junior Member

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    Hi there! Glad you got your problem resolved- but beyond the list of what Tampa Hybrids did, which one fixed the issue? Did they comment on which looked line a problem- stuck throttle, low transmission fluid, dirty battery fan...

    Just curious.
    Thanks,
     
    #10 paulcummings55, Jul 6, 2015
  11. paulcummings55

    paulcummings55 Junior Member

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    thanks
     
    #11 paulcummings55, Jul 6, 2015
  12. bisco

    bisco cookie crumbler

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    most likely the throttle cleaning. not the tranny fluid and only the fan if you carry animals regularly.
     
    #12 bisco, Jul 6, 2015
  13. lyvisky

    lyvisky Junior Member

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    Yes--bisco is right. Throttle body cleaning most likely did the magic. Todd at Tampa Hybrids is a gem! We bought a SECOND 2006 Prius from Todd and recently sprang for a grid charger and two harnesses from HybridAutomotive.com. Todd installed the harness on our original Blue Prius last week. We rebalanced its hybrid battery with the new grid charger this weekend (easy!) and already see improvement in performance. We'll get the harness installed on the Silver Prius soon and do the same. Needless to say, we are very Happy Campers!!
     
    #13 lyvisky, Jul 6, 2015
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