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Daytime lights turn off w/turn signal? (normal, but why?)

mattnh55

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Hey,

While driving, I noticed my nice looking daytime lights reflection in the truck ahead of me.. When I used my turn signal, I noticed the daytime lights for that side turn off while the signal is on... I was perplexed and thought it was a problem, but then noticed a newer GMC model do the same thing with their lights..

It appears normal - is there a reason? It seems a little strange -- and is awfully pronounced at dusk before the auto-sensor turns on the headlights.
 

Telluride Forum

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Hey,

While driving, I noticed my nice looking daytime lights reflection in the truck ahead of me.. When I used my turn signal, I noticed the daytime lights for that side turn off while the signal is on... I was perplexed and thought it was a problem, but then noticed a newer GMC model do the same thing with their lights..

It appears normal - is there a reason? It seems a little strange -- and is awfully pronounced at dusk before the auto-sensor turns on the headlights.
That aggravates me as well. I notice it with a lot of other brands, too... Especially Audi, for some reason. The Genesis vehicles don't do it...
 

jazzyone

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The SX doesn't do this since DRL is the turn signal.

All other trims do it. My guess is that it definitively shows other drivers that you have turned on your turn signal, otherwise they may be distracted by the very bright, white DRL.

BTW, the white DRL remains ON when you flip your turn signal ON if the headlights are ON.
 
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Buckeye-TRide

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It’s a federal regulation in the US...definitely not a style thing
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utmeep

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Prohibited combinations. (1) A turn signal lamp must not be combined optically with either a head lamp or other lighting device or combination of lighting devices that produces a greater intensity of light than the turn signal lamp.
So legally saying, you can't use your headlights at the same time as your turn signals....
 

Gwyn

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If you are headlight or other lighting device is in the same housing unit as signal then they have to dim. Which is why the headlights have to dim.
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jazzyone

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If you are headlight or other lighting device is in the same housing unit as signal then they have to dim. Which is why the headlights have to dim.
Actually headlights don’t dim, the DRL turns OFF. As a matter of fact, if you keep the headlights ON, then the DRL doesn’t shut OFF even when the turn signal is switched ON.
 

Gwyn

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Actually headlights don’t dim, the DRL turns OFF. As a matter of fact, if you keep the headlights ON, then the DRL doesn’t shut OFF even when the turn signal is switched ON.
Some dim. Some turn off. As for the last, it legally should. Especially if the DRL is the same color as the blinker.
 

Buckeye-TRide

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G

G-603723

Hey,

While driving, I noticed my nice looking daytime lights reflection in the truck ahead of me.. When I used my turn signal, I noticed the daytime lights for that side turn off while the signal is on... I was perplexed and thought it was a problem, but then noticed a newer GMC model do the same thing with their lights..

It appears normal - is there a reason? It seems a little strange -- and is awfully pronounced at dusk before the auto-sensor turns on the headlights.
It's so that the DRL doesn't obscure the turn signal light.
 

bogie

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If you want to see the 'letter of the law', continue reading; if not, save yourself now and stop reading 🤯:

>TITLE 49—Transportation
>> Subtitle B—OTHER REGULATIONS RELATING TO TRANSPORTATION
>>> CHAPTER V—NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION
>>>> PART 571—FEDERAL MOTOR VEHICLE SAFETY STANDARDS
>>>>> Subpart B—Federal Motor Vehicle Safety Standards
>>>>>> §571.108 Standard No. 108; Lamps, reflective devices, and associated equipment.

[Commonly referred to as 'FMVSS 108 '. Which is very similar to the Canadian version CMVSS 108; except Canada requires DRL (US allows them) and Canada allows European style headlights (US does not)]

The Specific section:
S7.10 Daytime running lamps (DRLs)

S7.10.10.1 Spacing to turn signal lamps. Each DRL not optically combined with a turn signal lamp must be located on the vehicle so that the distance from its lighted edge to the optical center of the nearest turn signal lamp is not less than 100 mm unless,

...(a) The luminous intensity of the DRL is not more than 2,600 cd at any location in the beam and the turn signal lamp meets 2.5 times the base front turn signal photometric requirements, or

...(b) The DRL is optically combined with a lower beam headlamp and the turn signal lamp meets 2.5 times the base front turn signal photometric requirements, or

...(c) The DRL is deactivated when the turn signal or hazard warning signal lamp is activated.

FWIW
 

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I noticed this on a Telluride I was passing yesterday. Never knew it was a thing.
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