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bizarre display problem - light switch and speedo

Discussion in 'Generation 1 Prius Discussion' started by Johnunit, Jan 30, 2012.

  1. Johnunit

    Johnunit New Member

    Joined:
    Jan 4, 2012
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    Location:
    Toronto, Ontario
    Vehicle:
    2001 Prius
    Model:
    N/A
    I have an annoying issue going on that just started. I'm not sure if the problem began during driving or what, but i don't believe I made any changes or did anything unusual (reading codes, changed settings, drained battery, etc.) leading up to this


    When I turn my headlights on, the ENTIRE display up top that houses speedo, fuel gauge, gear indicator, etc. goes to half brightness like it should for a second and then goes pitch black. Even in darkness there is no visible action going on. The green "headlights on" light still works, as do the other conventional warning lights, turn signals, etc, but nothing involved in the digital display lights up. It appears to act totally normally with the headlights off (ie. when the cluster isn't being asked to dim). It does go to the half brightness when the headlights come on but goes dark after about a second.

    Restarting and dozens of tries of just flipping the lights on and off didn't help, neither did giving the dash lovetaps. I'm really not sure even where to start with diagnosis. Clearly the fuse is still good, and if there's anything along the lines of a conventional breaker it's not being activated unless it resets instantly, because it will do the dim then off multiple times a in a matter of seconds if I flip the lights. It's like the software is confused?

    Anyone run into this before or have any theories?

    The blink of my tail lights while I checked my speed confused the heck out of some drivers, and isn't a long term solution.
     
    #1 Johnunit, Jan 30, 2012
  2. alekska

    alekska Active Member

    Joined:
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    Location:
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    Vehicle:
    2005 Prius
    It's possible that displays like the one in Prius have 2 sets of cathode (heated) elements: one for full brightness, and one for half. Or it could be the same single cathode fed a reduced voltage. Either the half-brightness cathode is bad, or the circuitry that provides reduced voltage is not functioning right. In either way fixing will require removing the board with display and related electronics, and examining.

    Also I would check the potentiometer that changes the brightness (if you have one: I do in 2005)

    Just my 2 cents

    - Alex

     
    #2 alekska, Jan 30, 2012
  3. 3prongpaul

    3prongpaul Hybrid Shop Owner, worked on 100's of Prius's

    Joined:
    Jul 18, 2010
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    Location:
    Boulder Hybids, Boulder, CO
    Vehicle:
    2006 Prius
    Model:
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    Check the "roller dimmer dash light switch" to the left of the steering column on the dash itself...maybe it's flakey.
     
    #3 3prongpaul, Jan 31, 2012
    2 people like this.
  4. Johnunit

    Johnunit New Member

    Joined:
    Jan 4, 2012
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    Location:
    Toronto, Ontario
    Vehicle:
    2001 Prius
    Model:
    N/A
    that was the issue. Dimmer roller thing. spun it up and down a couple times, flipped the lights on, and bingo bango I'm back to knowing what's ahead of me AND how fast I'm going to hit it.

    This forum is a godsend.
     
    #4 Johnunit, Jan 31, 2012
  5. ejensen

    ejensen Junior Member

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    Jan 31, 2004
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    Location:
    Philadelphia area
    Just wanted to add a huge thanks here. I had exactly the same problem and was contemplating taking the car in for service this week. Thought I'd check here first, and now the problem is fixed! Thanks so much.

    Eric
     
    #5 ejensen, Apr 22, 2012
  6. spikemichael

    spikemichael Junior Member

    Joined:
    Dec 31, 2018
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    Location:
    Washington
    Vehicle:
    2001 Prius
    Model:
    I
    In the opposite situation just started. The lights are full daylight mode and at night I can't get them to dim. It's a 2002 and rolling the dash pot makes no difference at all. For the sake of knowing, same situation in auto mode as in lights on mode.
    It's BRIGHT in here. The ONLY thing new is I replaced the 12v battery and immediately this problem began.
    I am at a loss.
     
    #6 spikemichael, Oct 9, 2023
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