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DRL Bug?!!!

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by gvp1995, Oct 18, 2016.

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  1. gvp1995

    gvp1995 Active Member

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    I was very happy to find DRL+ auto combination on my Three Touring. Yesterday I discovered a strange thing, which I attributed to some freakish accident. But today it has repeated. So now I think it is either a hardware or a software issue.

    At work I park in an underground parking lot which is rather dark. Dark enough for the car to turn headlights from DRL to ON (an icon on the display shows). Then I just turn off the car and leave. In the evening when I start the car, again the headlights are ON, which is fine. But when I go outside it never goes back to DRL.

    When I switch to OFF and then back to Auto, I get back my DRL, as it is supposed to be. But if I don't, the headlights are ON. I was driving for at least 10 min before noticing this.

    Another observation. Today the same thing happened. I switched to OFF and back to Auto. Then I drove in another dark parking lot, again the headlights turned ON. But this time I did not turn off the car. As soon as I was outside, the DRL was back.

    Did anybody else experience such behavior?!
     
    #1 gvp1995, Oct 18, 2016
  2. alanclarkeau

    alanclarkeau Senior Member

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    What country are you in?

    (there are a number of different variants of DRL operation, depending on country.)
     
    #2 alanclarkeau, Oct 19, 2016
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  3. fuzzy1

    fuzzy1 Senior Member

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    The circuit or system that makes the decision which setting to use, must have some hysteresis (Hysteresis - Wikipedia) built in. When it makes a choice, it tends to stick with that choice until the conditions change by more than some minimum amount. In many systems, this minimum is adjustable, at least at the design end, not necessarily at the consumer end.

    Without hysteresis, the decision making element will find threshold conditions where it flickers or chatters or 'hunts' for the right setting, and may never find it. The frequent changes trying to find the right setting can be merely annoying, or quite disconcerting, or possibly even dangerous.

    When you shut the lights off then back on, the system gets to make a fresh decision which setting to use, without regard to where it was previously, so no minimum change is involved.
     
    #3 fuzzy1, Oct 19, 2016
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  4. Coast Cruiser

    Coast Cruiser Senior Member

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    That sounds like 2001 a space Odyssey.

    the "HAL 9000" gets emotional. :LOL:

    When it's a gloomy or very cloudy, sometimes I like to drive with the parking lights on. That gives me DRL's upfront and the red taillights in back.

    But yesterday, the DRL's did not come on when I turned on the parking lights.

    Just another Prius oddity…
     
    #4 Coast Cruiser, Oct 19, 2016
    Last edited by a moderator: Oct 19, 2016
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  5. bbald123

    bbald123 Thermodynamics Law Enforcement

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    An excellent description! I will be borrowing this to explain the phenomenon to others in the future.
     
    #5 bbald123, Oct 19, 2016
  6. David Beale

    David Beale Senior Member

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    Pearl S has always been this way. If it bothers me I manually turn the lights off (from "auto") then back to "auto". However, having the lights on is not a "bad thing" (tm). Sometimes the morons will actually SEE you before they hit you. ;)
     
    #6 David Beale, Oct 19, 2016
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  7. RCO

    RCO Senior Member

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    Sorry to pop your balloon here, but whenever you select heads or parking lights, it should lose your DRLs. ;)
     
    #7 RCO, Oct 19, 2016
  8. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Yeah, this is a peeve of mine too. Maybe the guy's James Bond, lol.

    Anyway:

    upload_2016-10-19_7-46-11.png
     
    #8 Mendel Leisk, Oct 19, 2016
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  9. gvp1995

    gvp1995 Active Member

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    Yes, this is precisely what happens. I received a direct confirmation this morning when the headlights stayed ON for some time, but after I drove in a sunlight it changed to DRL.

    After I thought about it, indirect confirmation would be the fact that I did not notice this behavior for the first several weeks whet the sun was higher in the sky.
     
    #9 gvp1995, Oct 19, 2016
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  10. alanclarkeau

    alanclarkeau Senior Member

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    Agreed - with so many variants depending on the country of purchase, and with members in at least a dozen countries, maybe PriusChat should make a compulsory inclusion of "COUNTRY".
     
    #10 alanclarkeau, Oct 19, 2016
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  11. fuzzy1

    fuzzy1 Senior Member

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    It happens even with the dumbest of electrical elements, such as a simple level comparator. It's dark out, so turn on the lights. Now, it is lighter out there, above the trip threshold, so turn the lights back off. Now it is darker again, turn the lights back on. Ad infinitum. An unintended oscillator has been built, a very common problem in control systems. Hysteresis is one way to stop that oscillation.
    On my U.S.-market Gen3, the DRLs stay on when I switch to Park lights.
     
    #11 fuzzy1, Oct 19, 2016
    Last edited: Oct 19, 2016
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  12. gvp1995

    gvp1995 Active Member

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    Criticism accepted. Profile updated.
     
    #12 gvp1995, Oct 19, 2016
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  13. gvp1995

    gvp1995 Active Member

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    Mine too. Played with this yesterday
     
    #13 gvp1995, Oct 19, 2016
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  14. Coast Cruiser

    Coast Cruiser Senior Member

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    You never know what it's going to do on my GEN4. Sometimes the DRL's are as bright as the regular headlights, and at other times they are more dim. Sometimes they come on with the parking lights, and sometimes they don't. :LOL:

    I'm going back to simplicity… Headlights all the way ON, or all the way OFF. I guess I'm stuck in the 1970s. :D
     
    #14 Coast Cruiser, Oct 19, 2016
  15. RCO

    RCO Senior Member

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    DRLs = daylight RUNNING lights.
    Not for parking. Have to say, some national requirements for these are somewhat questionable imho!
    :((n)
     
    #15 RCO, Oct 19, 2016
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  16. gvp1995

    gvp1995 Active Member

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    It depends to which subject the word "running" is applied. Auto? or Lights?
    - lights when the car is running?
    - or running lights
    I was thinking more about how this thing works, and this 'minimum change' is a bit confusing to me. This is my pure speculation, I don't know how this implemented in reality, but here is a simple set up with the effect of hysteresis, that does not require to remember/subtract any values for 'minimum change'.

    Let us say, for simplicity, we are in AUTO mode, and the headlights are turned ON at light level 10 (whatever this may be) and lower. And they are turned OFF, and consequently DRL - ON at level 20 and up. The grey zone 10 to 20 just retains status quo and DRL is a default.

    This would explain all the behaviors I observed: when going from the garage to the street headlights stayed ON because the light level did not reach 20. When I turn OFF and back to AUTO the headlights did not go ON because the light was not below 10, etc...

    In such set up all the values are absolute, meanwhile 'minimum change' implies some relative value.

    Or maybe this is exactly what you meant?
     
    #16 gvp1995, Oct 19, 2016
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  17. MichelleStone

    MichelleStone Senior Member

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    All of this is too confusing. I'll just use Auto. I have yet to drive my car while it's dark outside. I've had the car for two months and haven't driven it at night!
     
    #17 MichelleStone, Oct 19, 2016
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  18. krmcg

    krmcg Lowered Blizzard Pearl Beauty

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    I use auto. I really don't know which lights are on and which aren't. I can see perfectly well.
     
    #18 krmcg, Oct 19, 2016
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  19. gvp1995

    gvp1995 Active Member

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    After realizing it is not a bug but a feature, I too will continue using my 'Auto' + DRL. The only one small issue for me is when I wait for someone and don't want to waste the energy. In such infrequent case "OFF" then back to "Auto"
     
    #19 gvp1995, Oct 19, 2016
  20. gvp1995

    gvp1995 Active Member

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    When headlights are ON you see an icon on the display. To verify DRL is ON I check the reflection of the car in front of me. Thankfully we have a lot of cars around :)
     
    #20 gvp1995, Oct 19, 2016
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