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12 volt battery

Discussion in 'Gen II Prius Technical Discussion' started by epoch_time, Dec 2, 2009.

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  1. epoch_time

    epoch_time Member

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    I received my 2009 prius in January 09 and measured the 12 volt battery drain at .54 amps while vechile is parked.
    I tried every combination of locking doors, turning off dome lights, turning off keyless entry nothing would reduce the current drain on the 12 volt battery, still measuring .54 amps.
    Note turning off keyless entry activates inhibit pin of smartkey ecu and disables keyless entry but does not reduce current drain on 12 volt battery! Drain is still at .54 amp.
    A website that does plug in prius hybrid conversions (EAA-PHEP) reports 12 volt current drain at .62 amps. And Schematic for prius shows many ecu's (body,theift,smartkey,ecu's and a couple of others) powered through the dome light fuse.
    Removing the dome light fuse reduced the 12 volt current drain to .24 amps. I didn't
    remove anymore fuses to see where the rest of the current drain was occuring.
    Researching the web I found that prius's are delivered to the dealers with the dome light fuse removed.
    I then estimated (guessed) the current of each ecu powered through dome light fuse, of which there are at least 6 ecu's powered while the prius is parked, to be .09 amps each and this accounted for the .54 amp drain thus I assumed this drain on the 12 volt battery was normal.
    I then installed trailer hitch type of electrical connector in the prius grill so I could plug it into, a bench type adjustable 14 volt 3 amp power supply with digital readouts of current and voltage, at night.
    I then pluged the 12 volt prius in every night for 11 months.. The current drain was never lower than .54 amp.
    After my third dead battery while parked at by girlfriends house without plugin capability. I finally resolved the 12 volt current drain problem !
    This third occasion of a dead 12 volt battery resulted in 24 hours of the prius being parked in cold driveway.
    I went to start the prius just to charge the 12 volt battery. The doors unlocked as normal I put the car in accessory position first to view battery voltage at my cigarette lighters permently installed walmart voltmeter and saw only 8 volts and quickly went to ignition on position but instrument pannel guages were erratic and relays were clicking so I turned system off.
    Then proceeded to connect 14 volt bench supply and noted several relay clicks then all was quiet and charging (I thought).
    After about 10 minutes of charge I tried to open backdoor hatch but it failed to open. Climing into drivers seat the is saw the instrument pannel was still on an dim. Pushing start button several times I finally managed to turn everything off.
    The first time I tried and thought I turned system off apparently there was not enough voltage to turn off the system or else the start button ecu was locked up.
    I allowed the car to charge for several hours got into the drivers seat started the car and noted the fuel gauge and scan-guage both show no gas when in fact I had 6 gallons.. scan-guage indicates 0.00 gallons but engine is running all is charging..
    I also got the warning triangle with message on screen saying parking lock is not engaged instructing me to pull car to level ground and engage park button.. I was on an incline in drive way with emergency brake on I put car in neutral and pushed park button, warning indicators went out park light illuminated all seems mormal except fuel gauge still shows empty.
    After about 5 minutes of analyzing things stoping and starting car I still show no gas but car is still on driveway incline. So I back the car out to level ground and after about 30 seconds my gas guage shows half full and scanguage shows 5.00 gallons.
    I conclude that gas tank and transmission ecu's lost memory due to low voltage and erratic
    indicator lights, and relays blinking and clicking while trying to charge battery with low current supply and using only 24 gauge telephone wire to supply voltage to the fuse block jump start terminal.
    This charge arrangement worked well on the two previous dead battery occasions without any erratic indicatiors or relay clicks but battery was deader on those previous instances and those times I could not activate start button due to deader battery.

    Everything normal till next morning, while pluged into my 12.8 volt bench supply I see only .09 amp of current draw instead of the usual .54 amps. I start doing tests everything I can think of.
    Hurray after 3 day of operation my car it consistantly only pulling less than .09 amps (probably closer to .06 amps after 24 hours).

    Conclusion The prius ecu's are of the highest quality cpu's with low power sleep modes, achievable after 100 second of the car powering down.
    My prius with backup cam, heated mirrors, smart key, theft system (not enabled), vechile stability, and tire pressure monitor, had one or more of its ecu,s stuck in nonsleep mode keeping one or more the computer busses (networks) active leaving possibly several ecu's active instead of sleeping.
    Thus my poor prius, and I suspect other prius's has been awake for many months draining the 12 volt battery..
    I suspect the ecu's nonsleep mode is a result of the dealer's arc and spark jump start methods.
    I believe that simply disconnecting the 12 volt battery should reset all ecu's enabling sleep mode of all computer busses and cpu's.
    A search of ecu sleep mode on the internet shows B M W ecu's have sleep mode and report that BMW should draw .04amp after ecu's are reset.
    Someone suggested removing 12 battery and shorting plus and minus battery cables together for 20 minutes and then turning ignition switch off to reset ecu's (I don't know when they turned on the ignition switch?).
    I would suggest putting a 12 volt pannel lamp across battery cables to drain off any capacitive charges rather than short batt cables together.
    The low voltage dead 12 volt battery condition did not erase trip odometers, seatbelt & reverse beep settings, radio presets as is the case when dome light fuse is removed.
    But this low voltage with low amperage battery charge attempt resulted in erratic displays and clicking relays and reset transmission ecu (didn't know it was in park) and fuel ecu (it didn't think there was any gas) and probably reset other ecu's thus fixing my battery drain problem. I hope this fixes or helps anyone else with battery issues.
    I used to be parked about 36 hours before getting a dead battery (warm weather) I calculate I should get 9 days without dead battery now. My battery is probably not in good condition after going dead 3 times now.
    1 person likes this.
  2. Politburo

    Politburo Active Member

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    Please edit your post to correct the word wrap issues.
  3. ceric

    ceric New Member

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    Hard to read, but I did it.
    Thanks for the post, nonetheless.
  4. richard schumacher

    richard schumacher shortbus driver

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    This is the root problem:

    "my cigarette lighters permently installed walmart voltmeter"

    Some fault in that voltmeter, or in the installation, has been draining the 12V battery. When the 12V battery voltage gets low enough, the low voltage causes all of the other weird symptoms including the bus related errors and incomplete shutdowns. Remove the permanently installed voltmeter, return the cigarette lighter wiring to its original condition, and the current drain will go away. Then buy a new 12V battery (Toyota or Optima Yellowtop) and all of the dying-battery related weirdness will stop.
  5. epoch_time

    epoch_time Member

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    I wasn't very clear about my cigarette lighter plugin voltmeter sold by walmart.
    ie; By permently installed == its pluged into cigarette lighter socket
    and I never remove it.. the cigarette lighter wireing is orignal & unmodified and is powered down when the ignition is turned off.
    And therefore not draining the prius battery.
    It draws 40ma when turned on. Has a tiltable display that I tilt upward against the dash to somewhat hide its existance when I park the car in public areas.
    And I recomend this voltmeter to any car owner that likes to monitor the 12 volt system . the readout is backlighted and displays in 1/100th of a volt increments.. plugs in and out of cigarette lighter as needed..
  6. jayman

    jayman Senior Member

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    Your parasitic load is 540 mA?!

    I've never recorded >35 mA with my '04 Prius

    Something is seriously wrong. All I can suggest is a subscription to All Data DIY, study the wiring diagrams, and start pulling fuses ONE at a time, until you eliminate that huge draw
  7. richard schumacher

    richard schumacher shortbus driver

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    Ah! Thanks for the clarification.

    You bought the car new, right? Why not let a dealer diagnose and fix this under warranty?

    Are there any dealer-installed or aftermarket electronics in the car? If so then all of them are suspect.

    Do you ever leave the car in ACC or IG-ON for more than a few minutes at a time? It's possible that the very first battery drain was caused by that, or by leaving a door ajar overnight, and everything since has been a symptom of low battery voltage.

    Was the car ever in an accident serious enough to do any electrical damage? If yes, then I can only advise taking Jayman's advice, and wish you luck finding everything.
  8. epoch_time

    epoch_time Member

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    Was 540ma now its between 30-40ma (my meter resolution is 10ma
    increments and now reading .03 amp) and has been constistant at that draw (30-40ma) for 5 days now.

    I all ready have the prius wiring diagrams..
    The current drain problem is fixed... its fine now... problem solved...
    One or more ecu's were not going into low power sleep mode...
  9. epoch_time

    epoch_time Member

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    You understand that I fixed the problem, don't you ?
    The current drain is now 30-40ma.
    The problem was one or more ecu's not going into sleep mode.
  10. richard schumacher

    richard schumacher shortbus driver

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    We hope :_> That ECU may have been damaged by the arc-and-spark. Also, a 12V battery that has been drained three times is not long for this world. When its voltage drops below 12.0, weird stuff will happen, so be prepared to replace it sooner than later.

    And stop using that dealer. He's bad news.
  11. Hytec

    Hytec New Member

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    What is "arc-and-spark"?
    What damage does it cause?
    How can it be detected if a dealer performed it?
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