2010 MFD Goes Dark When Headlights Go On

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Indy John, Jan 3, 2020.

  1. Indy John

    Indy John Member

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    Haven't driven at night for a while, and when I turned the parking lights and/or headlights on last night the MFD and other "dash" lights went dark. Only the "Ready" light and seat belt reminder stayed on. Headlights and parking lights off, they came back. With headlights on, I checked that all bulbs were lit. No codes showing and the 12-volt battery tests 12.8 volts, 375 CCA, and 100% life. Any thoughts?
     
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    The dash lights are supposed to dim, by design, when the headlights are turned on. I think. Try playing with the brightness dial, low, to the left of steering wheel.
     
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  3. iskoos

    iskoos Active Member

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    I would second what Mendel said above. The same happened to me once and I panicked. It was the brightness dial.
    And once I put some paper document on dash and moved it forward so it doesn't slide off while driving. I lost the left screen. I realized the paper I placed blocked the projection(or maybe reflection would be the right word):).
     
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  4. Indy John

    Indy John Member

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    Thanks, but they go dark/off/disappear completely, not just dim. Dimmer dial doesn't bring them back.
     
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  5. Mendel Leisk

    Mendel Leisk Senior Member

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  6. AzWxGuy

    AzWxGuy Weather Guy

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    In consideration of the 10 years of dust that may have accumulated in the potentiometer, I would try several full-range manipulations of the dimmer dial making sure to move through the clicks at either end of the range. I might personally go as far as spraying some contact cleaner into the dial, but this might not be good for the various plastics in there. Failing this, maybe a fuse?
     
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  7. ASRDogman

    ASRDogman Senior Member

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    If you turn the all the way ON, past the little bump you feel, the display will be at full brightness,
    as it is during day driving. If you go just past the bump, when you turn the lights on the display will be dimmer.
     
  8. TMR-JWAP

    TMR-JWAP Senior Member

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    Definitely something in the dimmer circuit.
     
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