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Gen 2 Prius Won't Start-not the 12 V Battery

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by DrBob4248, Jul 26, 2020.

  1. RobertK

    RobertK Member

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    If your headlights don't work you have a problem with the 12V system in the car. The 12V battery will allow the headlights to turn on regardless of the "Ready" state of the car. I'd start by checking the 12V battery and its connections, especially where the negative 12V battery cable bolts to the body. New batteries can be defective, or you might have a bad battery connection. If that checks out, check the 12V voltage at the underhood jump point with a multimeter and see that it matches what is available at the battery terminals. If that matches, you probably have a problem with a fuse or the wiring beyond the jump point.
     
  2. DrBob4248

    DrBob4248 Junior Member

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    The fuse for the OBD port is fine-I checked it. Headlights don't work. It's definitely a weird pattern.
    Might be time to investigate NPR's Vehicle Donation Program! My plan was to sell this vehicle so at this point it doesn't seem to make much sense to pour any more money into it. I just wish I at least knew what the problem was, but paying for a tow 40 minutes to the dealer doesn't seem like a good use of cash.
     
  3. fotomoto

    fotomoto Senior Member

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    Hmm. Check the 12v battery connections at BOTH ends; especially the neg. to the frame (it's hard to see and reach). It's either an 8 or 10 mm bolt head.

    I guess you're not hearing any relay clicks from the HV battery when you try to start the car?
     
  4. DrBob4248

    DrBob4248 Junior Member

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    When trying to start the car, with the first press of the Power button, nothing happens except green light on the power button. With a second push, the Check Engine light comes on, there is a click and a humming noise under the hood and the brake pedal firms up.
     
  5. fotomoto

    fotomoto Senior Member

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    OK, as I like to say, a hybrid is an electric vehicle and the state of health of BOTH batteries is paramount. Seems 12v is fine so suspect HV battery next. Rebuilt batteries are still old batteries.

    GOOD LUCK!
     
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  6. sam spade 2

    sam spade 2 Senior Member

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    Well the 12 V SYSTEM is not fine if the headlights won't come on.
    AND the simple fact that the battery is new proves NOTHING about it's health or state of charge.
    It also proves nothing about the main 12 V cable connections.

    Before he junks the car, he should at least put a meter on the battery and/or connect it to a charger overnight.
    And check those cable connections too.

    We are 25 posts into this thread and I think that has been suggested about 3 times now......with no response from the OP.
     
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  7. DrBob4248

    DrBob4248 Junior Member

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    That's because the OP has to get a multimeter.
     
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  8. bisco

    bisco cookie crumbler

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  9. DrBob4248

    DrBob4248 Junior Member

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    Okay. The multimeter shows the 12V system is good. 12+ volts at the battery. 12+ volts at the charging terminal under the hood. I also have voltage at the OBD terminal even though the OBD reader won't even turn on. And the fuses are all fine.
    To me, this suggests it's not the hybrid battery, but perhaps the ECM/computer. Of course, I know almost nothing about this, so I could be totally wrong.
     
  10. bisco

    bisco cookie crumbler

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    12+ volts is not necessarily good. a new battery is 13 volts

    more importantly, what is the exact voltage, and what does it drop to after the headlights have been on for 5 minutes?
     
  11. ChapmanF

    ChapmanF Senior Member

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    That's plain weird. You mean that literally, as in the reader does not power on? It would be good to get a reading of that voltage while you have the reader attached. (Which could require popping that diagnostic connector out of its cutout in the dash, and using a backprobe.

    Yeah, they just don't break that often, though. For some reason the computery thing is always something people want to suspect, but it's also the solid-state no-moving-partsy thing and problems usually turn out to be somewhere else.
     
  12. JC91006

    JC91006 Senior Member

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    Your 12v battery is good, no need to keep going on about this non issue. At this point it's also shouldn't be the hybrid battery cause it's not even getting to the point of the car needing it to start the car.

    Just for fun, replace the AM2 fuse (the one you checked) and see if anything changes.

    I'm still suspecting rodents ate some wires

    Matt at Texashybridbatteries.com is an expert here on the forums. If he's not far from you, maybe you can give him a call. He will know how to troubleshoot the car and he will come to you without you needing a tow
     
    #32 JC91006, Jul 28, 2020
    Last edited: Jul 28, 2020
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  13. sam spade 2

    sam spade 2 Senior Member

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    Yep. Could be. :)

    The + on your 12+ readings is really important.

    If there is no load on the battery, it should read about 12.8 volts, assuming it is an OEM AGM type.
    12.0 is a bit more than half discharged and may not be enough to work right when a load is applied.
    With no load, anything below about 12.4 is suspect......as it might go WAY down when a load is applied.
     
  14. sam spade 2

    sam spade 2 Senior Member

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    Nope. Sorry. The 12 V battery system has not yet been proven good.
    Still could be a weak battery or a bad main connection.
     
  15. JC91006

    JC91006 Senior Member

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    get past it already, read post #29. He bought a new battery and he measured over 12v. What more do you need?
     
  16. sam spade 2

    sam spade 2 Senior Member

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    "Over 12 V" is not accurate enough.
    And there are other things that can cause low voltage......like corroded connections.
    If "getting past it" means thoroughly testing and inspecting it and THEN moving on......I fully agree.
    OTOH, if it means ignore that because of assumptions.......that is not good practice.
     
  17. dolj

    dolj Senior Member

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    When you press on the brake pedal, do you see the brake lights light up?
     
  18. Longinus876

    Longinus876 Junior Member

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    Very good description of all variable. How did it work out for you? What was the final result?