Brake Light on occasionally at startup

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Motamedi, May 18, 2011.

  1. Motamedi

    Motamedi New Member

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    Brake Light on occasionally at start up

    I have a new-to-me (2 weeks) 2004 Prius, and my wife has noticed a weird behavior on start up which I have not been able to reproduce.

    Occasionally when she starts up the car the brake light comes on as if the parking brake were set. The ready light will not be on. No other warning or error lights come on. If she turns off the car, and then turns it on again the light will be off and not return. Tapping or setting and releasing the parking brake has no effect. She swears it has nothing to do with her pushing the parking brake or not pushing the pedal brake. This seems to have started after I set the parking brake one afternoon, but that could also be coincidental.

    Combing these forums I could come up with two possible causes.

    First, that my 12V battery is dying.

    Second, that the parking brake switch is faulty. This seems possible, however according to the description of TSB BR002-007, the failure is mechanical, wherein the "switch... swivel out of position and NO longer make contact with the parking lever." I can't see how turning the car on and off would effect this. (The forum software won't me post the URL to the TSB, but you can find it easily enough by searching this forum)

    I have ordered a new Optima D51 battery (testing shows it a bit low), anything else I can do, short of ripping the dash apart and looking a possibly faulty switch?

    Thanks in advance.

    jason
     
    #1 Motamedi, May 18, 2011
  2. Corwyn

    Corwyn Energy Curmudgeon

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    I wouldn't do any ripping apart until you can replicate it. (no offense to the wife) Hunting for a bug you can't see is very difficult.
     
    #2 Corwyn, May 18, 2011
  3. 2009Prius

    2009Prius A Wimpy DIYer

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    #3 2009Prius, May 19, 2011
  4. VoicesInMyHead

    VoicesInMyHead New Member

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    Have you checked the brake fluid level? On many cars (not sure about the Gen II, I don't have one), the brake light will also illuminate when the brake fluid level falls below a certain point in the reservoir. Considering the Prius does some funky brake pressure preparation stuff, perhaps it's briefly falling below that threshold, causing it to illuminate.
     
    #4 VoicesInMyHead, May 19, 2011
  5. VoicesInMyHead

    VoicesInMyHead New Member

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    .. redacted .. realized I had misread 2009Prius's post.
     
    #5 VoicesInMyHead, May 19, 2011
  6. Motamedi

    Motamedi New Member

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    Thanks for the suggestions. I will check the fluid, switch, and refrain from ripping anything apart until later!
     
    #6 Motamedi, May 19, 2011
  7. mikewithaprius

    mikewithaprius New Member

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    Re: Brake Light on occasionally at start up

    Hey Jason,

    I know she swears she pushed the brake pedal, but the exact same "symptoms" would appear if you're in accessory mode (pushing the start button twice without foot on the brake).

    I did that once accidentally two weeks ago, and was scared to death when the car wouldn't shift to drive, even though it was already moving since I was starting out the first few seconds in neutral downhill to avoid the engine coming on ("Oh God, it's broken, it's BROKEN!"). The parking brake light wouldn't go off (but the brake itself was off), and there was no "ready" light. There are other lights, but I tended to notice the brake light in particular, too. When I realized there was no "ready" light I figured out what I did. I still don't know how I did it, since usually you'll push the button twice, and I definitely remember pushing it once, and since I was at a stop sign, my foot was on the brake (perhaps not hard enough). In any case, my memory and the reality don't add up, but it happened :)

    Those other things sound possible, but driver error also seems possible. Maybe remind her to push the brake pedal more firmly before pressing the start button?
     
    #7 mikewithaprius, May 19, 2011
  8. 2009Prius

    2009Prius A Wimpy DIYer

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    Exactly. If the car is not in READY mode but rather in IG-ON mode because the driving brake light switch wasn't triggered when the start button was pushed, then the brake warning light would illuminate. Hope this makes it clearer now.
     
    #8 2009Prius, May 19, 2011
  9. cyclopathic

    cyclopathic Senior Member

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    check brake fluid level, light may come on if parked on hill or going through corner
     
    #9 cyclopathic, May 19, 2011
  10. VoicesInMyHead

    VoicesInMyHead New Member

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    Yeah, I misread your post. Thx for the clarification.
     
    #10 VoicesInMyHead, May 19, 2011
  11. Motamedi

    Motamedi New Member

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    Thank you all. I hope it is human error, which will certainly prove to be cheaper than mechanical or electronic failure, at least in this case.
     
    #11 Motamedi, May 19, 2011
  12. Motamedi

    Motamedi New Member

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    No, I am now pretty certain it is not human error. My wife took a picture "to prove it to me" and the dash does not show any warning light on but the brake light. I went in after work to look at it in "IG-ON" mode, and it looks nothing like the picture she sent me.

    Back to square one. Any other suggestions?
     
    #12 Motamedi, May 20, 2011
  13. seilerts

    seilerts Battery Curmudgeon

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    Why haven't you posted the picture that she sent you?
     
    #13 seilerts, May 20, 2011
  14. mikewithaprius

    mikewithaprius New Member

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    Sounds like you should get it into the dealer then. You're already aware of the TSB that would potentially resolve this, and for others to read a bit about it, here's an older link:

    http://priuschat.com/forums/gen-ii-...ng/73869-parking-brake-light-wont-go-out.html

    The ready light not coming on is troubling, though, unless it goes hand in hand with this for some reason. Not sure why it would, though. Keep us updated when it's fixed.
     
    #14 mikewithaprius, May 20, 2011
  15. Motamedi

    Motamedi New Member

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    I didn't think a fuzzy picture of a dashboard with the brake light illuminated would add any important information to the conversation.

    I called my mechanic, who told me that if the light doesn't go on and there is no error code, all he can do is inspect the parking brake mechanism. Of course, I can do this as well.

    Thanks again for the help and advice.
     
    #15 Motamedi, May 20, 2011
  16. 2009Prius

    2009Prius A Wimpy DIYer

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    #16 2009Prius, May 20, 2011
  17. Motamedi

    Motamedi New Member

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    Thank you, I am aware of the TSB.
     
    #17 Motamedi, May 20, 2011
  18. seilerts

    seilerts Battery Curmudgeon

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    Technically, there are warning four lights associated with the braking system. Just wanted to know if we were all on the same page. Looks like you received about all the help here that you care to accept.
     
    #18 seilerts, May 20, 2011
  19. Motamedi

    Motamedi New Member

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    Indeed, I have received some excellent advice. Thank you.
     
    #19 Motamedi, May 20, 2011
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