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12 volt battery - What could cause a 2.00 Amp drain?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Braddles.au, Aug 16, 2012.

  1. Braddles.au

    Braddles.au DEFAnitely using an EBH

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    Location:
    Canberra, Australia
    Vehicle:
    2010 Prius
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    Nearly dead battery tonight. Enough to get into the car and run the brake pump, but not enough to start. The lovely Justin from Allianz Roadside Assistance (other roadside assistance providers are available) found 7 volts at the battery. Battery is OEM Toyota replaced March 2012, car is Gen III NVW30 built May 2009, 79911km (50,000 miles)
    On the weekend I went medieval with the vacuum and carpet sprinkle, so the doors were opening and closing for hours but the LED interior lights were off. I had a short drive after finishing. I haven't driven since and the nights have been -3°c to -5°c. So the 7 volt reading is probably no surprise and my own fault. :rolleyes: Justin attached the jumper and the car started fine. The alternator was pumping 40-45 Amps into the 12 volt battery; it could sense that it was in need of a charge.

    What could then cause a 2.00 Amp drain?
    Later with the battery charged a bit and the car switched off, his battery analyser found a 2.00 Amp drain. I had already unplugged the GPS and switched off all interior lights. The only things "on" where the rear hatch being open (but the light off) and a Garmin ecorouteHD attached to the OBDC port (but not receiving power AFAIK). I have just installed a DEFA EBH and the earth lead is attached to a post near the negative terminal under the bonnet (hood). Justin didn't think that the EBH earth lead or ODBC device when the car is off could cause a drain.
    This excellent analysis suggests that an open hatch draws 0.50 Amps (and the hatch was open) and a scan gauge has a cyclic drain. The ecoroute HD doesn't have any power connection other than the OBDC port and it relies on the separate Garmin GPS for its display.

    Justin suggested a proper diagnostic from Toyota.
    Any ideas where 2.00 (or 1.50) Amps could be going?
     
  2. hlunde

    hlunde Member

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    Location:
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    2010 Prius
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    III
    Normal practice is to install an ammeter in series with the battery and remove one fuse at a time until you seen the current diminish to what is normal -- something like a few 10's of millamperes.
     
    Braddles.au likes this.
  3. Braddles.au

    Braddles.au DEFAnitely using an EBH

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    Location:
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    Vehicle:
    2010 Prius
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    Good tip... but I wondered how I could read a meter at the opposite end of the car while testing fuses. I found an Auto Current Tester at my favourite waste of time Jaycar for $19.95.
    [​IMG]

    The end fits standard fuses, so I can test from the fuse box. Jaycar has another (that I can't find on-line) for $59.95 with peak hold and data hold and a range of fuse sizes. This would be useful for finding spikes and intermittent faults, but I'll take one steps at a time. Note: Its operating conditions are limited to 2000m (6500 ft) for some reason.

    Question: How long should I wait after switching off the car/opening or closing a door/etc. before testing if I want a basal "metabolic" rate measurement?
     
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  4. electric1

    electric1 Junior Member

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    Did you ever find the root cause? My 2010 does the same thing, quiescent current about 1A drains a fully charged battery in 3 days.
     
  5. Braddles.au

    Braddles.au DEFAnitely using an EBH

    Joined:
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    Location:
    Canberra, Australia
    Vehicle:
    2010 Prius
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    I haven't had a chance to do the diagnostics. Since I've been busy and the weather is getting warmer, it hasn't been a high priority.
    I might try this weekend.
     
  6. The usual rule in troubleshooting is to look at the last place worked or installed. To eliminate any surprises I disconnected all my courtesy light and only use dome light manually . Never had any more problem on my 2005 once I did that. With that ammeter you have there, one person can monitor while a partner turns on equipment, ONE AT A TIME. With the car off and a 2 Amp drain, sounds like a miswire, ie: hot wire to ground. DAMI,DAMI..