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Headlights Fail When Braking

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by xAARONx, Feb 13, 2015.

  1. xAARONx

    xAARONx New Member

    Joined:
    Feb 6, 2015
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    Vehicle:
    2007 Prius
    Model:
    II
    As an avid do-it-yourselfer, I've found a lot of useful information on this forum to assist in the care-and-feeding of our 2007 Prius. However, I've encountered a problem that has me stumped and I haven't found a solution for it here. I thought I'd seek help before I continued to spend money on unnecessary items that don't repair the problem.

    We've persistently had issues with the HIDs in this car the past couple years. Normally one would start blinking before ultimately failing (but work temporarily if the headlights were turned off/on again.) I would replace the bulbs which would last about 6mo, maybe a year.

    After replacing them the last time around and the problem persisting, I purchased a set of HID ballasts and replaced them and yet the problem continues with a new more concerning problem: Both headlights fail under moderate or heavy breaking and will not come back on unless the car is turned off/on. However, if coasting to a stop or lightly breaking the headlights will stay on.

    I'm unsure where to continue troubleshooting at this point. I don't know if there is a problem with the ECU when it comes to braking, a possible problem with the alternator or 12v battery or I've got a pair of faulty ballasts?

    Anyone have any advice on what to try next?

    TIA!
     
    #1 xAARONx, Feb 13, 2015
  2. Britprius

    Britprius Senior Member

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    Location:
    Herefordshire England
    Vehicle:
    2008 Prius
    I think you need to monitor the 12 volt battery while braking. It is difficult to see why the headlamps should be affected while heavy braking, and the only conclusion I can think of is that.
    Under heavy braking the hybrid battery is charged at a rapid rate rising it's voltage. This sudden rise may affect "with a faulty DC/DC converter" raising the 12 volt rail voltage, and affect the ballasts for the HID's.
    The opposite effect could also apply that as the hybrid battery voltage rises the DC/DC converter shuts down suddenly lowering the 12 volt rail. Again affecting the ballasts or there output.
    The Prius does not have an alternator in the normal sense.

    John (Britprius)
     
    #2 Britprius, Feb 14, 2015
    Last edited: Feb 14, 2015
  3. xliderider

    xliderider Senior Member

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    Location:
    Honolulu, HI
    Vehicle:
    2011 Prius
    Model:
    Three
    A Scangauge can give voltage readings. Our Gen 3 typically runs at 14.X volts, where X is typically 3 or 4 while in Ready Mode.

    A multimeter might also be used to measure the voltage, but you will need someone to watch it while you drive and engage the regenerative braking system.

    As Britprius indicated, there is most likely a surge or drop in the system voltage when the regenerative braking is engaged, which is causing the problem with the HID ballasts.
     
    #3 xliderider, Feb 14, 2015
  4. JimN

    JimN Let the games begin!

    Joined:
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    Location:
    South Jersey
    Vehicle:
    2010 Prius
    Model:
    V
    A 2007 Prius would need a Package 4, 5, or 6 to come with HID. Would one of these cars have an upgraded component to power the HID that a Package 2 doesn't have?
     
    #4 JimN, Feb 16, 2015
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