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12V battery? alternator? electrical gremlin?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Ohrockclimber, Nov 30, 2015.

  1. Ohrockclimber

    Ohrockclimber New Member

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    Alright. So I've had this car for about a year and no warning lights are on. However I used to get about 420miles per tank, it has been dropping the past 3 months and I'm now getting 320 a tank. (sign 1)
    (sign 2): sometimes when I turn off the car, headlights off, and I hit the lock button and get out of the car, when I close the door the car automatically unlocks itself. If I try to lock it from the outside it again unlocks itself. If I drive it around the parking lot and then turn it off again this generally fixes the issue.
    (sign3). periodically (often coupled after I didn't fix sign 2 by driving around, but not always with sign 2) the car will not turn on. It struggles to get power apparently as if you try to use lights or wipers the wipers are very slow. After trying to turn it off and on a few times (anyway from 1 - 15 times) the car then starts and runs fine, sometimes periodically having the same hiccup if I turn off the car, but generally doesn't persist to the next day.
    (sign4) Yesterday it would NOT start. When I would try to turn it out only the Engine light would come on. I jumped the 12v battery and it was good to go immediately, no warning lights. I got the battery and alternator tested at AutoZone and the battery was coming back good at 83%, and the alternator was coming back at 13.5v (which should be enough in theory but a bit low).

    Any idea if sign 1 and 2 are related to sign 3 and 4? And is it as simple as an alternator even though the alternator isn't coming back terribly low?
     
    #1 Ohrockclimber, Nov 30, 2015
  2. The Electric Me

    The Electric Me Go Speed Go!

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    Since The Prius doesn't have an alternator, I think you can cross that off the list.

    I'd go with failing 12 volt battery.
     
    #2 The Electric Me, Nov 30, 2015
  3. Ohrockclimber

    Ohrockclimber New Member

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    Well its good to know that there isn't an alternator. Could it be the inverter then?
    I will try to replace the 12v but it seems odd it is reading good. Would a failing 12v cause issue 1 and 2?
     
    #3 Ohrockclimber, Nov 30, 2015
  4. The Electric Me

    The Electric Me Go Speed Go!

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    If it's the original 12 volt battery it easily could be time for a replacement.
    As a Prius's 12 volt weakens all types of reported "Gremlins" can appear.

    To be honest, not sure if your symptoms manifest from any other area of your electrical system, including inverter. Others may have better suggestions, as far as what to look for or test.

    I am sure it's not the non-existent alternator.
     
    #4 The Electric Me, Nov 30, 2015
  5. bisco

    bisco cookie crumbler

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    welcome! how many miles on her? yes, it could be the 12v. buy a digital volt meter for 10 bucks and learn to test it yourself. it's an expensive battery, might as well be sure.
     
    #5 bisco, Nov 30, 2015
  6. Ohrockclimber

    Ohrockclimber New Member

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    It is a 2009 with 78,000 miles. I'd rather shell out for a new 12v then take it to the dealer for them to figure it out, esp if it is such a minor issue. The 12v appears to be the original one from the dealer, so I'm sure id have to replace it here soonish anyways.
    Thanks in advance for any further advice!
     
    #6 Ohrockclimber, Nov 30, 2015
  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Replace the 12V battery.
    2. During those occasions when the doors will not lock, are you sure that all doors and the hatch are securely closed? If they are all closed and the lock system will not lock, maybe one of the switches that indicate a door/hatch is closed is getting flaky. What about the cabin lighting, do the lights remain on when the car will not lock?
    If the lights remain on, that obviously will quickly deplete the 12V battery.
     
    #7 Patrick Wong, Nov 30, 2015
  8. fuzzy1

    fuzzy1 Senior Member

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    #8 fuzzy1, Dec 1, 2015
  9. ChapmanF

    ChapmanF Senior Member

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    The way my driver's door actuator failed was: it slowly grew weaker and weaker (less torque relative to input voltage) so that it was sometimes unable (rarely at first, later often) to move the lock mechanism all the way to 'locked'. The switch indicating 'locked' state was not flaky; it correctly reported to the computer that the door was not successfully locked, and the computer reacts by doing an unlock a couple seconds later, hoping you notice. It was baffling why my car was re-unlocking as I walked away from it, and I finally caught what was happening by walking to the other side of the car and peering through the window while sending a lock command from the fob. I could see the driver door lock knob wiggle a little, but never move all the way to locked, and then the car would give up and unlock again. That was fixed when I replaced the lock actuator.

    While the actuator was weak, of course the effect was more noticeable in cold weather when the door linkage was stickier, or when the voltage from the 12 V was lower.

    This is one of the few times on PriusChat where the reflex "could be your 12 V battery!" seems like it could be genuinely helpful. I'll mark the calendar.

    If battery replacement does improve the symptoms, I would guess that a door lock actuator is also not far in your future (an actuator in like-new condition probably wouldn't be having trouble at marginal battery voltages).

    -Chap
     
    #9 ChapmanF, Dec 1, 2015
    Patrick Wong and koolingit like this.
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