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Questions around IG ON mode: batteries, ECUs

Discussion in 'Gen 2 Prius Technical Discussion' started by 2009Prius, Oct 27, 2010.

  1. 2009Prius

    2009Prius A Wimpy DIYer

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    In the IG ON (not READY) mode, is the HV battery being used for something? Are all the ECUs turned on and communicating? How long would the 12 V battery last if fan is minimal and A/C is off? The reason for asking is to do some OBD stuff whether in ON or READY mode. Thanks!
     
    #1 2009Prius, Oct 27, 2010
  2. jdcollins5

    jdcollins5 Senior Member

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    In both ACC (one push of Power button without brake) and IGN ON (two pushes on Power button without brake) you are only connected to the 12V battery. The HV battery is disconnected. In IGN ON you can operate basically everything inside the car, the radio, the windows, the doors, etc.

    The 12V battery on the Prius is smaller than normal since it does not have to start the ICE. So, be careful running too long in IGN ON. The best thing, if you plan to spend much time at all, would be to do it in Ready mode. This way the ICE can fire up when needed to recharge the HV battery which in turn recharges the 12V battery.

    As for the ECU's, they are communicating in both IGN ON and READY modes.
     
    #2 jdcollins5, Oct 27, 2010
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  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The traction battery is disconnected until the car is READY. You may be able to hear the system main relays engage as the car becomes READY if the hatch trim over the battery is removed.

    The ECUs are all on. The 12V battery should last at least a couple of hours while IG-ON if in good condition and fully charged.

    Your decision regarding the OBD-II "stuff" in IG-ON vs. READY will depend upon what you are trying to measure.
     
    #3 Patrick Wong, Oct 27, 2010
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  4. 2009Prius

    2009Prius A Wimpy DIYer

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    Thank you! I thought the HV battery is disconnected unless in READY also, but the SOC shown on ScanGauge went from 58.5% down to 57% during ~ 20 minutes of IG ON time, maybe the battery ECU was adjusting itself?

    Various instructions of OBD equipment call for IG ON but engine not running (supposedly not READY in case of Prius). Not sure why.
     
    #4 2009Prius, Oct 27, 2010
  5. seilerts

    seilerts Battery Curmudgeon

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    There's nothing wrong with hooking up a 12V charger or portable jump starter while you have the car in IG ON. In fact, for ECU reprogramming, this is a requirement, since losing 12V power during reprogramming results in a ruined ECU.

    Its not unusual at all that the HV battery ECU would show a change in SoC after the car is in IG ON. SoC calculation is a mix, I think, of Coulomb counting and a lookup table of voltage and temperature at zero current. When first turning IG ON, it would report the last known value, then recalculate based on the observed voltage and temperature.
     
    #5 seilerts, Oct 27, 2010
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