2005 Prius - 12V battery keeps dying despite repairs/replacements

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by PixelShigoto, Jun 17, 2020.

  1. PixelShigoto

    PixelShigoto Junior Member

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    This has been a long road since it started in October, so I'll try to summarize.
    I've had to go to 3 dealership shops through this. I'll number my regular place as #1.

    October:
    Event:
    Gas engine cuts out on the freeway. Master light and check engine light turn on. I try to make it to the next exit but run out of hybrid battery power after a minute and have to pull over. While waiting for a tow, the 12V battery is drained. No codes in the computer.
    Repairs:
    Dealership shop #2 says it's the 12V battery and the computer needs to be reflashed/updated.

    January:
    Event:
    Same problems occur.
    Repairs:
    Dealership shop #3 tries to diagnose, can't find anything. They run a warranty on the 12V and replace it.

    February:
    Pre-event:
    I go in for regular maintenance at my usual place, dealership shop #1. They can't find anything wrong and replace a headlight that has been out since August.
    Event:
    Gas engine cuts out on the freeway, but this time I pull over right away. I call dealership shop #1 and they tell me to try to restart. I manage to restart the engine and get back to dealership shop #1.
    Repairs:
    The inverter water pump failed, and was replaced.

    June:
    Pre-event:
    I've only driven every 2 weeks for a half-hour at a time since mid-March because of COVID-19. I've had to work from home most days, and only get to go in when it's absolutely necessary.
    Event:
    On my way to work, the gas engine cuts out again. Master light on, check engine light on. This time, I'm able to restart the engine by using a jumper pack I got, but the same failure happened twice as I limped back home.

    I'm going to go in tomorrow to get yet another diagnosis/repair. I'm afraid it might be the DC-to-DC converter, which as I understand it is costly to replace. I've already had to replace the hybrid battery in 2018, the last time I posted here.

    When I checked the voltage of the 12V using the maintenance mode on the MFD, it read:
    11.3 V (headlights on)
    11.8 V (headlights off)
    14+ V (upon jumping the engine, then the MFD exited maintenance mode)

    I have a multimeter in the garage and will go read the voltages from the engine compartment and from the battery connection points later on today.

    Any insight on what the hell is going on would be much appreciated. If this requires a costly repair or a new car, I guess I can go back to living off rice and beans again.

    Thanks in advance
     
  2. bisco

    bisco cookie crumbler

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    how many miles on her?

    when you get the trouble codes, post them here.

    ar 14v, sounds like the converter is working. maybe something is draining your 12v. you would ave to measure the draw with the car off. but it seems like there's ore going on than that. the codes will point you in the right direction
     
    SFO likes this.
  3. PixelShigoto

    PixelShigoto Junior Member

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    I've got about 97k miles on the car and have regular maintenance.

    I grabbed my multimeter and got these readings:
    Front measurement point: 11.9V idling, 14.4V running.
    Back measurement (on the battery itself): 11.9 idling, 14.0V running.
     
  4. TMR-JWAP

    TMR-JWAP Senior Member

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    My experience has been that a brand new 12v battery will last no more than 8 weeks in an unused Gen 2 before being completely drained by the cars parasitic loads.

    I've only driven every 2 weeks for a half-hour at a time since mid-March because of COVID-19. I've had to work from home most days, and only get to go in when it's absolutely necessary.


    I would be extremely surprised if this amount of driving was sufficient to maintain the 12v battery adequately charged.

    My initial thought after the first 2 paragraphs was that you had the inverter overheating, most likely from a failed inverter cooling water pump. Nailed it, as you then stated...The inverter water pump failed, and was replaced.

    If the check engine light is on, then there are codes stored. They need to be retrieved. Any good shop should have an electronic 12v battery tester. That should be one of the first things they check. I don't care if the 12v battery is new or not, they need to connect a tester to it and see it's current state. A weak 12v will lead to a lot of tail chasing.

    Along with that, techstream software should be used to communicate with the car to see all the codes and troubleshoot. Many code readers are not able to pickup the hybrid codes. Also, if all codes are clear, it could be an indication that 12v power is being lost, since disconnecting 12v will reset all the car ecus and clear all codes.
    Something simple is being overlooked and I'm betting this whole thing would be an easy fix if you were a bit closer to me.
     
  5. PixelShigoto

    PixelShigoto Junior Member

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    I've got the SKS feature and I know that's nibbling away at the 12V charge over time. I guess I'll need to do a weekly drive now if it's parasitic loads draining the battery.
     
  6. dolj

    dolj Senior Member

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    It's not a fix, but to mitigate your problems a bit in the interim, press the 'Key' button under the steering wheel in. In the 'in' position, this disables the SKS feature and lowers the quiescent draw on the 12 V when the car is sitting unused.
     
  7. Albert Barbuto

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    A trickle charger/battery maintainer for the 12v battery is used by many people, to keep the 12v fully charged. I use one myself, as many trips I take are too short for proper battery charging.
     
  8. PixelShigoto

    PixelShigoto Junior Member

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    The shop cited a technical bulletin that prescribed updating/reprogramming the ECU. The bulletin number cited was EG047-04

    They pulled these codes off the car:
    P3190
    P0A0F

    I'll go look up these codes and update the thread. If anyone else recognizes these I'd appreciate your input. Thank you for your support!

    Edit:
    There was a similar thread here that covers the codes:
    Prius died randomly today, TSB EG047? | PriusChat

    Quoting from one of the replies:
    "
    P3190 = Poor Engine Power. Engine has started but torque output is below 20% of expected torque. Reported by engine ECM.

    P0A0F = Engine Failed To Start. Reported by HV ECU - this may be associated with the P3190 code.

    My understanding is that the update described in EG047-04 TSB simply extends the amount of time before the ECM will decide that the engine hasn't caught - it'll crank a bit longer. That doesn't sound like your problem.

    The P3190 code is likely the root cause of your problems, and the recommended course of action is:

    - Check the air induction system (intake) for leakages or blockages
    - Check for unusual noises or vibration
    - Check the fuel pressure
    - Inspect mass air flow meter
    - Inspect engine coolant temperature sensor
    - Inspect crankshaft and camshaft position sensors
    - Inspect throttle control motor and position sensor
    - Replace the ECM
    "

    Other posts I've read so far have cited things like the throttle body needing cleaning. I'll call the shop back and ask if they inspected these issues as well.
     
    #8 PixelShigoto, Jun 19, 2020
    Last edited: Jun 19, 2020
  9. bisco

    bisco cookie crumbler

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    was that update done in oct. with the reflash?
     
  10. PixelShigoto

    PixelShigoto Junior Member

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    Unknown, regarding what they actually did in October. I'm convinced that dealership shop just wanted to me off - I've since learned that the 12V battery I had then was still under warranty, but they charged me full price and even more for the "reflash".

    I called my regular place. They explained that, for now, the ECU update should be sufficient.
    If the low gas engine power was due to the other possible causes (blocked air intake, air mass flow sensor issue, or dirty throttle valve) there would be other codes present to indicate those. If the car stalls out again, then they'll do more diagnostic tests to check for the other possibilities.
     
  11. edthefox5

    edthefox5 Senior Member

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    What was the "regular maintenance" done to the car? Throttle body has never been cleaned before I bet. At that mileage its a mess.
    How often do you check the oil? Should be once a week before starting the car on a G2.

    Not driving the car for days and days is really bad for both battery's. The 12 volt battery at 11.9 is bad and not holding a decent charge.
    Its sulphated..And not driving will shorten the hybrid battery life too.

    Get a voltmeter.. Measure the 12 volt dc volts with the car OFF at the front jump point. Then with car still off turn on the headlights in high beam.
    Leave them on for 5 minutes. Turn them off after 5 mins. With car still off wait a minute them measure the dc voltage at the front jump points
    again. It should not have dropped at all not 1 volt. The battery should have been able to hold hat. If any degradation in voltage after this test the battery is sulphated. It may respond to a recondition if not too old. Your 11.9 battery will fail this test.

    A healthy G2 Prius battery lives at 12.6 volts sitting there with engine off.

    It is really really quick to throw a battery tender on the front jump points.Probably all of a minute It will extend the life of the 12 volt battery for years. Just leave it on the car the whole time your not using it. been doing it to my car for 13 years and never any 12 volt battery dram. In fact it will warn you the battery is getting bad.

    The 12 volt battery is the last thing in your world you should be messing around with in a prius. So easy to cause major $$$ damage with 12 volt battery shenanigans.

    Buy a tender. I own a Citek MUS 4.3 that has recondition mode it works good i throw it on my 12 volt all the time. Things to watch out for is it cannot fully charge the battery that means the battery is toast and will leave you. You will never know unless you get involved.

    A G2 Prius should be driven every day in fact a high mileage prius does the best with its hybrid battery. They do not like sitting.
    A battery sitting and draining over long periods of time will create corrosion on its connectors.

    If you cant drive the car everyday and cant tender the 12 its not the car for you. It will just b a hassle. Thats why at 100,000 miles you had to put a new hybrid battery in it. .
     
    Albert Barbuto likes this.
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