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My '08 Prius is having some weird electrical problems. Is this a bad battery, or something more?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by wowbobwow, Jul 18, 2013.

  1. wowbobwow

    wowbobwow Junior Member

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    Some of you might recall my previous post a couple months ago, wherein I detailed a crash and the subsequent repairs to my 2008 Prius Touring Edition. I got the car out of the shop a few weeks ago (she spent more than a month being rebuilt), and for the most part she's been as good (or better!) than when I bought her in Feb. of this year. After all the repairs, she runs great, looks like new, and even gets slightly better MPG than before (probably due to the oil change I had done while they had her in the shop).

    However, for the past 3 days she's been acting really weird in some specific ways (listed in no particular order):

    • A few times when I've parked and tried to power the car off by hitting the Power button, rather than just turning off, she has gone into that partially-booted mode you get when you hit Power while the car is off *without* pressing the brake pedal. When this happens, I've had to putz around with the brake, Power, and open/close the drivers-side door before she would fully power on and then (when I hit the Power button again) power off. Weird.
    • Starting yesterday (or maybe once the day before), when I try to power up from being completely shut down, nothing happens. Nada, zip, zilch. As above, I end up putzing with the key-fob, putting it into the dash socket, removing it, opening the drivers door, etc. Eventually (and apparently randomly) it will just power on like normal and drive like normal
    • This morning I walked up to the car to leave for work, and the doors wouldn't unlock. I ended up using the physical key from within the fob to open the door, and spent ~10 minutes poking around with the Power button and the little button near my knee that allows / disallows the keyless-start feature. On one unlucky attempt to get the car to power up, the anti-theft alarm went off - I'm sure my neighbors loved that at 5:10am. Eventually she powered up just fine and I got to work with no trouble
    • However... once I arrived at work this morning and powered her down, she immediately lost all power, and is currently sitting in the parking lot with all the doors unlocked (because I can't lock them from the outside)
    • Finally, and I have no idea if this is related: the little "bump" within the drivers-side power window rocker (the thing that rolls the window all the way up or down without holding the rocker) suddenly stopped working late yesterday. When the car is powered on, I can roll the window up or down, but I have to hold the rocker - pressing it to active the auto-roll feature does nothing
    While I was sitting in the parking lot this morning, I looked up the trick for accessing the Diags menu, which report my battery with 13.9 volts... which seems a bit odd for a 12-volt battery. None of the other symptoms I've read about seem to apply - no random beeping, my lights are nice and bright, etc.

    Sorry for the long post - I figured an info-dump of everything I've observed might help!

    Thanks for any suggestions.

    TL;DR: 2008 Prius acting weird, suddenly has no electrical power when the motors aren't powered on. Wth?
     
  2. pjc

    pjc Member

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    Loose connection somewhere? Maybe your shop forgot to tighten something down. You could start with the cables on your 12V battery.... Or maybe there is a relay somewhere that didn't get pushed all the way into its socket....? I would just start poking around in all the electrical terminations (fuse boxes, etc.) and see if something is loose or out of whack (fuse blown, etc.)
     
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  3. nh7o

    nh7o Off grid since 1980

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    Yes, especially the ground connection to the battery. The 13.9V reading is not what you want. You need to get the reading with a load on, like headlights. That should tell you something. Also, use a voltmeter to poke around and look for problems.
     
  4. uart

    uart Senior Member

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    Please start by making a correct measurement of the 12V battery voltage. The 13.9 volts that you measured was the DC-DC converter voltage, not the battery voltage.

    - Repeat the procedure you did today, BUT this time start with the Prius in accessory mode (press power button with foot off the brake pedal). This reading would typically be about 12.0 to 12.4 volts.

    - Once you get the above reading then press the power button on more time (again with foot off the brake pedal). This reading would typically be about 11.8 to 12.2 volts. You should definitely be concerned if it's less than 11.5 volts.

    NOTE. Make the above measurements after the Prius has been sitting (not been in ready mode) for at least 4 hours. So make sure you don't place the Prius in ready mode prior to the test, you need to go straight into accessory mode. (So keep foot off brake pedal!)
     
  5. wowbobwow

    wowbobwow Junior Member

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    and thanks for the helpful and detailed checklist! My first attempt to perform the test you suggested accomplished nothing, as the car was playing paperweight and refusing to do anything at all. I turned into a contortionist, pulled all the stuff from the back, lifted the floorboard and tray, got the rear hatch open, and jiggled all the wires going into / out of the battery. After doing this, suddenly I had power again, so I tried your test and got the following results:

    First test: 12.1 volts
    Second test (after hitting the Power button): 11.9 volts

    Those numbers are well within the normal range, right?

    I did notice that the connection to the "positive" terminal isn't rock-solid - the battery cable is fairly loose and can wiggle around a bit, though it's fully seated around the post. Now I'm wondering if this is just a case of minor corrosion on the battery terminals causing a poor connection...

    Any further thoughts? I'm thiiiiis close to dropping $200 (that I can't really afford) on a new battery...
     
  6. pjc

    pjc Member

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    Don't buy a new battery yet. Clean your + terminal (if it looks corroded) and clamp it securely. It should not wiggle at all. Also check your other connections. I don't think this is a battery life problem based on what you've posted.
     
  7. uart

    uart Senior Member

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    Yeah it seems ok.

    If by "had power again" you mean that you were able to get to "ready" mode (start the Prius in the normal way) then you should wait a few hours and test again. Remember that the test should be done after the car has been fully off for several hours.

    I agree with pjc though, you definitely should remove, clean and tighten both your positive and negative battery terminals (including the ground strap where it connects to the body).
     
  8. wowbobwow

    wowbobwow Junior Member

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    Thanks everyone for the advice and feedback! I just finished cleaning the terminals and reseating the connectors - so far, so good. I'm going to take her on a drive, but I'll hold off on the replacement battery for the time being.

    I freaking love this community - I've only been a Prius owner for a couple months, but I've seen more kindness and helpfulness from you all in that time than in the 10 previous years as a VW owner. Really, thank you all! :)
     
  9. easted

    easted Junior Member

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    I had basically the same thing happen to my 2007 a while back. It had spend a few months in a repair shop getting body work done after a long time just sitting while the insurance company made up there mind about whether to repair or not. It turned out that the long stretch of not running (no 12v battery charging),was enough to discharge the 12v battery, and this long time sitting discharged killed the ability of the battery to hold a charge. I had to have the battery replaced, and I was able to get the insurance to pay for it.
     
  10. Patrick Wong

    Patrick Wong DIY Enthusiast

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    If this should happen again, lock the doors manually. Note the rotary door lock knob on the inner door panel of each door which shows red when unlocked.

    To open the driver's door, use the key hidden in the fob, to open the driver's door lock. I suggest you try opening this lock before you actually have an emergency so you'll know what to expect.

    Make sure the 12V negative terminal cable is securely bolted to the body.

    I suggest that you put the 12V battery on a battery charger overnight, hopefully that will help to extend its service life. If the battery is original, it is almost six years old so don't be surprised if it needs to be replaced.