Originally Posted by blittle

So here's the story as provided by my Tech guy ( we spent about two hours working with this )......basically two parts: 1. if you have a vehicle with the optional LED running lights, then... when you program the the option to
"leave running lights on all of the time" the "auto/off" function of the rotary switch is overridden and the system is "always on" and the sensors ( rain and light on the windshield ) will be determining whether all of the lights are on or just the lowbeams or nothing at all except the LED DRL's. In other words, if the headlights should come on and you want them OFF... turning the rotary knob to off will have no effect! Both the tech and I agree that this "dumb" engineering but nevertheless is the way it is programed and no upgrades are available as yet. Part 2...... With regard to the headlights coming on when the vehicle is started in the dark and then NOT GOING OFF as the day brightens: the light sensor actually responds to the infrared spectrum.... and, amazingly, a bright or dark blue sky with the sun not directly overhead may be interpreted by the system as "dark" or not "bright enough" and the headlights stay on. The tech actually showed me the Mercedes "in house" service data on the subject: it's entitled "Blue Sky Effect"..... this can be frustrating and/or confusing for the customer. The system is designed to err on the side of lights being on "too long" vs. the potential for the lights "going off" too soon or unexpectedly. The onboard computer looks at the input data and then turns the headlights on or off based on the data..... it is not as simple as the senor seeing light or no light and turning the system on or off. They do have quite a diagnostic test for all of this and all data came back good on my vehicle............... in short, it's going to be this way until there is a better logic sequence in the programing. The good news is ...... there is nothing "wrong" and we will probably never experience the opposite of all of this: having no lights when we need them!

Originally Posted by WaveyKat

Question to anyone who has the LED DRL how do I get the DRL to stay on without the headlight being on?
I have a 2011 GL550.

Originally Posted by islandbeef

Complete instructions are in your owner's manual. Under "Daytime Running Lights" or something like that.

Originally Posted by CoastsideX164

Since this thread has been revived, does anyone know if there has been a fix for this annoying engineering mistake? Like a reprogram or something?

I keep my DRLs off now because otherwise my full headlights come on nearly all the time. I wish "off" truly meant "off" like in every other car on the planet.

Originally Posted by darkster

Nope it's still an issue, I thought I was losing my mind until I read this thread. I can't believe they programmed the system this way. It completely irks me that I can't leave my DRL's on without knowing that the first time I sit under a shade tree at a light, the full headlight system will turn on and stay on until I shut the truck off. #lame

Originally Posted by 007_e350

I'm coming from a bimmer, in that world DRL = on means the led angel lights on (like the led strip we have) and not the whole headlamp ... In GL world I accepted I have DRL option but I don't, that led strip won't light up on it's own, only with the headlamp on, maybe a Coder can solve this for us ? Dealership admittedly told me it ain't gonna happen....

Originally Posted by Jason B

actually you can, what you have to do is put the switch in the auto position, and as long as it's daylight outside they will be triple the brightness that they are at night.

Originally Posted by 007_e350

Oh cool, let me try that it's bright out rightnow