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Parasitic Draw Test on 2007 prius?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Dow, Nov 19, 2014.

  1. Dow

    Dow New Member

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    I'm doing a parasitic draw test to find out what is causing my battery to be dead in morning and the starting reading I'm getting is 0.15 amps. Is this normal? Cause I'm not finding any thing that changes the reading.
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    0.15A is much too high. 0.02A is more like it.

    All doors must be closed and locked when measuring quiescent current draw. If your car has the Smart Entry/Smart Start system, the fob needs to be more than 15 feet away from the car.

    0.15A x 24 hours/day x 7 days/week = 25.2 Ah/week. The 12V battery capacity when new and fully-charged is ~40 Ah. You are not supposed to let the battery discharge more than 50%. So if you started with a fresh, new, fully-charged battery and left the car unused for a week, the battery would be 60% discharged upon your return.
     
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  3. Dow

    Dow New Member

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    And Thank you Patrick Wong for your answer! Well I thought 0.02 was more like what I was looking for. could a window down or doors unlocked cause the 0.15 draw that I'm seeing? And I had the key about 20 feet away. What about the hood open I saw no light or wires indicating any source of power there.
     
    #3 Dow, Nov 19, 2014
    Last edited: Nov 19, 2014
  4. uart

    uart Senior Member

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    Hi Dow. When you open the door the Pruis senses this and activates some of the ECUs in readiness to power up, this gives the relatively high current draw you're seeing. If you keep all the doors closed then this mode should time out after a few minutes and it drop back to something more like 20 to 30 mA.

    Try this test.

    - Open the drivers door to pop the hood and then close it again.
    - Go around under the hood and check the 12V voltage at the jumper terminal (in the fuse/relay box) with a digital volt meter.
    - Wait around for about 5 minutes and you'll hear a slight click from that relay box as a relay drops out.
    - Check the voltmeter and you'll see the 12V voltage rise by a small amount as the current has now dropped.

    This will let you know when it's back to is true off mode standby current.
     
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  5. Easy Rider 2

    Easy Rider 2 Senior Member

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    Yes any of that can be a factor.
    In the end, it is likely that you are dealing with a battery that has exceeded it's useful life and NOT an abnormal parasitic drain.
    Most old and weak batteries fail completely after sitting overnight.
     
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  6. Dow

    Dow New Member

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    Thank You! both Uart & Easy Rider 2 for you answers to my post. I have another question about this could a tire air pressure sensor if its bad cause this?
     
  7. valde3

    valde3 Senior Member

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    You mean sensor inside the tire? No it’s not connected to car by any wire. And car doesn’t receive it signal if car is off.
     
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  8. Easy Rider 2

    Easy Rider 2 Senior Member

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    Cause excessive battery drain ? Nope. No way.
     
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  9. Dow

    Dow New Member

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    Thanks
     
  10. Dow

    Dow New Member

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    Thanks
     
  11. uart

    uart Senior Member

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    How old is your battery Dow?
     
  12. HammerGrips

    HammerGrips Junior Member

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    OK, I realize this is an old thread, but I'm puzzled and need some ideas. My 2008 Prius had a new Optima battery 3 or 4 years ago. We had to jump it a couple times this fall and I thought lights or something was left on. My wife isn't working anymore and we didn't really have anywhere to go anyway because of covid, so I removed the battery and brought it inside. It was weak and not charging, so I put in an extra battery I had in the shop. It was going dead, so again it was disconnected and the car just sat for the winter.

    It has finally warmed up enough and today I got around to trying to track down what's happening. I connected a battery with long jumper cables, so I could have a meter in series next to the fuse panel. It was reading about 12 amps with everything off. I pulled every fuse and relay, one by one, and it didn't change at all.

    Am I looking at rodent/vibration induced short somewhere? Maybe a circuit that isn't fused? It runs fine and lights are good, even with a compact motorcycle battery powering it up, so I'm guessing the charging circuit is functional. I drove it in for a shift at the radio station a few days ago because my wife needed the other car. I had the battery on the front seat with jumper cables going to the battery terminals in back. When I got there, I just removed one clamp from the battery.

    I'm open to your ideas and suggestions. Thanks in advance.
     
  13. chronon

    chronon Active Member

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    i connected my battery via ammeter .. measured <1 ma ? however when i make the connection it produces a big fat spark like 1 amp ... maybe its like startup current draw that dwindles down to trickle ... i thought disabling my keyless entry would reduce current draw .. but it seemed to say the same at .66 mA (that couldnt be .66 A could it ? )
     
  14. Mendel Leisk

    Mendel Leisk Senior Member

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    that’s way too high, obviously; should be around 20 milliamperes.

    When you did your measurement: every door on the car was closed, fob well away, fob detection button set to off, and everything had just sat for say half an hour?
     
  15. HammerGrips

    HammerGrips Junior Member

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    Yup.

    I did some more reading and discovered there's another fuse panel under the dash. I went thru all of those (and the 3 relays) and still no change. We did have some evidence of mice in the car a year or 2 ago. I'm wondering if they shorted some wiring somewhere... Are there circuits that are not fused? The engine runs fine and everything works, but my wife is not going to go for a driving around with a pair of jumper cables from the trunk to a battery on passenger seat.

    I'm still really puzzled...
     
  16. chronon

    chronon Active Member

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    yeah , when car sits for months and esp over a year .. the critters do their dirty work ..
    i have plate lights to diagnose.. they dont come on at all indicating likely an open to the 2 bulb sockets ..
    to get to them under the hatch panel .. not exactly easy access ...
     
  17. Mendel Leisk

    Mendel Leisk Senior Member

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    Eric expounds on troubleshooting parasitic draw here, might turn something up: