Gen 2 with 220K miles, sudden 10 mpg loss, 12V battery?

Discussion in 'Gen 2 Prius Fuel Economy' started by Bryan Holloway, Nov 30, 2016.

  1. Bryan Holloway

    Bryan Holloway Junior Member

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    I have been using 5W-20, inflated tires to 45 psi, and am still getting low mileage. The car seemed to do it out of no where when nothing changed. Im thinking its the 12V battery, my wife had to jump it 2-3 times recently accidentally leaving a door open and the overhead light on. I checked the voltage through the maintenance mode and it was above 12V and charged above 14V. So I concluded that the 12V wasnt an issue. Rear brakes also werent touched. The engine is burning oil, but I wouldnt think that I'd have a loss of power through the engine because of that? I dont know of anything else to try.

    Im thinking about just spending the $150 and get a new 12V optima. The 12V, Hybrid batteries, and trans were all replaced 4 years ago when we got the car at 150K miles. The logic behind a bad 12V sucking the charge from the system makes sense with the happening of the problem, but after testing it, it seemed fine? Is there another way to test this maybe?

    As for as the ICE engine goes, ive replaced plugs on it, PCV, air filter.
     
  2. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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    Simplest check would be to invest in a half-dent digital multimeter. Check voltage with the car off, at the under-the-hood jump point (assume second gen has this?). A battery in decent shape will read over 12.5 volt. A faltering battery: 12.2~12.4. Any lower, it's near dead, should be replaced, or you can attempt recharge. For more in-depth assessment, something like Solar BA5 will do an electronic load test, tell you the current Cold Cranking Amps of the battery, and give a verdict, either good, good but recharge, or fail.

    Any decent retailer selling automotive batteries you should have a pro-level equivalent to the BA5, be able to run the test for you.

    Doors open, lights left on, 4+ years old, needing a jump start? All this says it's time.

    You can look into chargers too: a smart charger in 3~4 amp range is what you need.
     
  3. Bryan Holloway

    Bryan Holloway Junior Member

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    I think at this point ill go ahead and just replace the 12V. I was worried about the ICE going out and thinking about getting a compression test done since im having oil burning and have ran it down to low levels accidentally a few times.
     
  4. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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    Yeah, could be other issues, but the 12 volt is the "low hanging fruit". If you don't want to get into tool investment, yeah: replacement is a good first step, considering it's age and what's been happening.

    But really, a $20 multimeter is invaluable first step, towards getting some insight into what you're 12 volts doing. Or just mundane stuff: like if you've got some lose AA batteries, and you're wondering if they're dead or good. Or small appliance repair, household wiring and so on.
     
  5. 05PreeUs

    05PreeUs Senior Member

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    I would rather KNOW if the 12v was suspect and if not, save the $200 for a new WB Oxygen sensor that is also a top contender for this issue.
     
  6. Bryan Holloway

    Bryan Holloway Junior Member

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    Is there a way to check and see if the WB sensor is good? Ive got a scan tool that reads out info when running. where is it located also?

    I tested the battery after a drive and its at 12.4V. I went ahead and bought the battery since its been awhile and have killed the battery 3-4 times.
     
  7. 05PreeUs

    05PreeUs Senior Member

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    Yup, the 12v is DOA.

    Bank 1, O2 1 is the WB on a Prius. Depending on what brand of sensor it is, it should read in the 2.5V+ range (stoich or trending lean), if <2v, it's running rich.
     
  8. Bryan Holloway

    Bryan Holloway Junior Member

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    So update here. Ive tried replacing the 12V battery with no success. It looks like my Bank 1 O2 1 is at 3.2-3.4V when driving, and 5V when decelerating. Is this within the 2.5V+ range you mentioned?

    I dont know what else to check. Im going to pull the plugs and try replacing, but I replaced less then 50K miles ago...
     
  9. Bryan Holloway

    Bryan Holloway Junior Member

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    Does anyone have any other ideas for trying to fix the loss MPG?
     
  10. bisco

    bisco cookie crumbler

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    what were your mpg's on your last full fill up, manually calculated?
     
  11. Bryan Holloway

    Bryan Holloway Junior Member

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    When I got the car it had 150K mile on it with new batteries and trans and it would never go below 49mpg on the information screen average. Now 70K miles later, it never goes above 41mpg. Ill calculate by hand on the next fillup, but it seems to have definitely dropped, and it seemed pretty sudden too.
     
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  12. bisco

    bisco cookie crumbler

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    have you always gone by the dash display for mpg's?
     
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  13. Bryan Holloway

    Bryan Holloway Junior Member

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    Yes I have.
     
  14. bisco

    bisco cookie crumbler

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    i'm sure there is some data to be mined there, but there are so many things changing so rapidly, it's difficult to get a handle on. most of us track our mpg' on fuelly or other, and it gives a better picture of trends.
     
  15. bisco

    bisco cookie crumbler

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    have you had any dash lights?
     
  16. Bryan Holloway

    Bryan Holloway Junior Member

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    Ive got the P0420 and have narrowed it down to needing a new CAT. Have tried cleaning the CAT, and new downstream O2 sensor with no luck. I can imagine the CAT making a difference but seems like too large of a change to be just a CAT.
     
  17. bisco

    bisco cookie crumbler

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    i'm not that knowledgeable. i suppose there are many items not performing up to spec on a high mileage car, that cumulatively, could add up to 10 mpg's.
     
  18. repnatl

    repnatl Junior Member

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    My 06 has 282k and my 07 has 162k and both use oil about a quart or two between oil changes but really depends on driving. Extended highway at 75+ I use more oil. A lot of newer cars use oil by design due to improper break ins. I just check it every couple fill ups as cheap insurance.
     
  19. 05PreeUs

    05PreeUs Senior Member

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    No OEM designs engines to use excessive oil amounts, for any reason and few engines require a break-in period, while many have not for a decade or more (in some cases, 3 decades). Typical high performance engine designs use dramatically more oil than a quart every 5k, which is what most OEMs aim for.

    You are spot-on, higher engine speeds will transmit into higher oil consumption rates. This is especially common with these cars.
     
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  20. TheLastMojojomo

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    I know this is a dead thread but just wanted to post a phenomenon I experience that could explain your MPG loss.

    It has to do with the 12v disconnecting/dying and resetting the Hybrid ECU's. The relearn parameters to return your Prius to max efficiency are not so straight forward. Explained in detail below.

    Hybrid System Less Efficient After 12V Disconnect



    Posted via the PriusChat mobile app.
     
    #20 TheLastMojojomo, Mar 2, 2021
    Last edited: Mar 2, 2021
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