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2001 normal 12V draw when off

Discussion in 'Generation 1 Prius Discussion' started by hoskee, Jan 18, 2010.

  1. hoskee

    hoskee New Member

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    I'm measuring .33 amp draw on the 12V battery when the car is off. This was measured with my multimeter in series. This is enough to discharge the battery in a couple days. What is normal? If this is too high I plan to pull fuses and possibly relays to isolate the circuit that is responsible. Is there are recommended order to check circuits?
     
    #1 hoskee, Jan 18, 2010
  2. adric22

    adric22 Ev and Hybrid Enthusiast

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    So that is about 4 watts. That is about the electric usage of leaving a map-light on or something like that. Have you been having trouble with your battery running down?
     
    #2 adric22, Jan 18, 2010
  3. hoskee

    hoskee New Member

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    I just got the car and the person who had it said he thought there was a short and to disconnect the ground to avoid running down the battery. So far I have had it start ok after leaving the battery attached overnight. I did have it not start after listening to the radio (cartalk of all things) for 20 minutes on acc but that would not be related to the draw when completely off. It would probaly point to the battery as the problem.

    Should I just go to a bigger battery and not worry about tracking down this small current draw? I'm going to commute in the car every day so I can actually avoid leaving it for too long without starting.
     
    #3 hoskee, Jan 18, 2010
  4. Eisbaer

    Eisbaer German Prius Driver

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    Hi hoskee,

    a small current drain is normal, even for the Gen 1 Prius, which e.g. does not have smartkey or something like that. But 0,33 A is quite a lot.

    I would go for a search. You feel better and in case of a longer parking period the battery will not run down.

    Try the following:
    When the car is off, pull one fuse after another until you see the current drop. You have three fuse boxes to look at: One in dashboard on the driver side and two in the engine compartment (see manual for detailed description).

    Maybe you start with the "dome" fuse in the dashboard, since it is responsible for most of the interior accessories.
     
    #4 Eisbaer, Jan 18, 2010
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The Classic Prius current draw should be more like 35 mA, or 1/10 of the value that you measured.

    I also recommend that you start with the DOME fuse, to see whether that circuit is causing the excess current draw.

    You can obtain the wiring diagram at techinfo.toyota.com
     
    #5 Patrick Wong, Jan 18, 2010
  6. hoskee

    hoskee New Member

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    On source of current turned out to be the trunk light. I hadn't noticed that there was a trunk light during the day but did just now at night. That accounted for .25 of the .33 amps. By pushing the trunk close switch in the latch I turned the light off and the amps were down to .08. Then I pulled the dome fuse and it dropped from .08 to .02 amps. That's now below the 35 mA that Patrick Wong said is normal (but I'm probably introducing enough resistance in my meter that it may actually be 35 mA).

    So now I'm looking for 60 mA in the dome circuit. Any suggestions? It does have the optional cd player. I wonder if that was installed properly.
     
    #6 hoskee, Jan 18, 2010
  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Good work, determining that the trunk light switch needs to be adjusted. I suggest that you make that adjustment so that the light is off when the trunk is closed. Then download the wiring diagram so that you can determine all circuits downstream of the DOME fuse. (I don't have access to that diagram this week so I can't suggest likely places to look right now.)

    I'm also concerned that the car is drawing 20 mA even when the DOME fuse is out. There may be more than one circuit drawing excessive current. Does the car have an aftermarket alarm installed?

    Regarding the CD player, you could disconnect the wiring harness connector leading to it and see what happens to the quiescent current draw.
     
    #7 Patrick Wong, Jan 18, 2010
  8. hoskee

    hoskee New Member

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    I tried it again today and now I do get 30mA when I make sure the trunk switch is in closed position and the car door is also closed. The car door draws 500MA even when the dome light is turned off. Locking the door even changed the battery draw. Someone mentioned that it is important to lock the doors to cut down battery draw so I will be doing that. I assume this is related to the security system.
     
    #8 hoskee, Jan 19, 2010
  9. Patrick Wong

    Patrick Wong DIY Enthusiast

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    OK, it sounds like your car's wiring is good now. The body ECU keeps track of the doors' status: open or closed, locked/unlocked (even if the dome light switch is turned off) so this is why the current draw differs.

    It also sounds like your 12V battery might need to be replaced, or at least fully charged before you put the car back in service.
     
    #9 Patrick Wong, Jan 19, 2010
  10. hoskee

    hoskee New Member

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    Is there any reason why I couldn't just add a deep cycle battery in parallel with the 12V battery?
     
    #10 hoskee, Jan 20, 2010
  11. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Yes, there are a couple of reasons:

    1. weight associated with having more than one battery
    2. mismatch where the two batteries have unequal capacity, hence one battery is drawing more current than the other

    If you want to install a deep cycle battery, then get one that fits the existing 12V battery space, can be attached to the existing vent hose, and has capacity of 28 Ah or better.
     
    #11 Patrick Wong, Jan 20, 2010
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