wannawagon

I have an 06 ML320 CDI which the headlights come on all the time

Maj Dundee was helping on a previous thread but I thought I would start with a new thread (after I have scanned) so it is more specific. (and perhaps helpful for someone else to find in future).

On advice I bought a better scanner and Autel DIAGLINK with MB only software and I am happy with it.

I have scanned it and despite a heap of other stored codes etc when I was working on the indicators (previous thread) nothing has come up with headlight, and the front SAM codes cleared (which were indicators)

I have swapped headlight switches with another car (2008 GL) and the switch worked fine in the GL, and the GL switch still did the same thing in the ML - which is as soon as the car is started the headlights come on (just low beam and the inner parker bulbs) - no matter which way the switch is (off/auto/on etc). High beam operates on request as it should

Are the headlights through the front SAM?

Is there a relay that could be stuck? If so where do I find it

I was thinking that if there is a relay that is not powered til the engine is running - and that relay is stuck on then it could be that.

The headlights used to behave correctly a few years ago but am not sure how long they have been behaving this way (now daughters car who lives away)

Obviously the car is driving etc but I am more concerned with stressing the charging system unnecessarily etc

kombifan

Have you checked and perhaps cleaned the sensor?

A few years ago I needed to have the light sensor reset because it too was coming on all the time. Perhaps Maj Dundee can give some more detailed information.

😉

wannawagon

Thanks for that - I thought the sensor would only have been activated when the switch was in the auto position?

Do you know where the sensor is? Just incase its dirty or something

kombifan

Behind the rear view mirror.

The sensor is activated in 0 and auto.

wannawagon

Is that the internal mirror (not the side ones?)

It makes sense for the inside one so its out of the weather - hope it is as I have a spare one (came with a motor I bought)

kombifan

Yes. The inside rear view mirror.

kombifan

I had a think...I don't remember if when I brought in the car for that issue that it got any better. It probably did get better....but I realised since I changed my rear view mirror with one from a 2012 model I've never had an issue with the lights turning on too early. Perhaps an updated part from a newer car will help. The problem you're having is widely documented. It's called blue sky effect. And mercedes has no solution for it.

It is a pain to get the mirror on correctly though.

wannawagon

Sorry about a starting a new thread if its known - maybe my wording on search was too specific

Thanks for that, I will try and get the mirror off and try the other one I have (it is out of an 05 so it may be a short fix)

I will report back

kombifan

https://mbworld.org/forums/m-class-w...erratic-5.html

wannawagon

Just a progress report

The spare mirror I have came with a sensor which I think is for the wiper, not the headlights.

I swapped the sensor over but the headlights still behaved the same (on when engine running) but the headlights went on to intermittent (which I assume is because the sensor was not attached to the screen).

The headlights will go off if put on to parkers (position 2)

It seems like a weird idea for MB to make the sensor live when the switch is in the off position - why?

At least the headlights are working. LOL

wannawagon

Thanks for the link - wow - its a long thread - am ploughing through it

Sorry I missed the reply earlier - I think the internet here is bad

kombifan

The one behind the mirror is the light sensor.

The rain sensor is when you look at the windshield from outside, it looks directly attached to he windshield and almost looks black/red.

The sensor is live to stop people from driving without any headlights.
I prefer it that way. You wouldn't believe how many people drive without any lights on at ntght. I think mb made the right choice.

wannawagon

so the sensor is actually in the mirror housing?

kombifan

On the back of the mirror housing. Does yours look different?

sorry mate I think I’m getting a bit confused as I haven’t had time to look at the parts diagrams.

I think uoure rifht. The rain sensor and light sensor is integrated in one. Although some older models did have the light sensor in the rear view mirror housing.

Really sorry about that.

I glanced through the thread I posted again, and for some even replacing the sensor doesn’t fix the issue. But I did have a thought... Is your windshield original or ever been replaced? Sometimes an aftermarket windshield or improperly calibrated sensor can cause it too.
If you have star, perhaps you can run the light sebsor reset function?

SunnyT

Did you try checking the menu on the instrument cluster controlled by the steering wheel buttons. The headlights can be used as an old school "DRL" before cars had fancy pants LEDs. Should be under Settings --> Lighting --> Headlamp Mode. There you can find the options "Constant" & "Manual". It might be worth a try to cycle these options (like unplugging it and plugging it back in). I know when I set it to constant the lights stay on 24/7 when the car is running. I guess they integrated it because in some countries its the law to always have your DRL or headlights (if you don't have DRLs) active for safety reasons. Might just be an electronic glitch that the car is experiencing, worth a shot nonetheless. Hope it's just a glitch and not another bad sensor.

wannawagon

Many thanks for both your suggestions, the term DRL is not a known one here so very possible it has been inadvertently switched - would explain the lack of codes when scanned...

The car is a away for an hour or two but I will report back after I have checked

I thought the sensor I had (off the spare mirror) looked right as it had a head of light type sensors on it 8 of one type, and another 1 that had a different lense

The screen looks to be aftermarket but it has been in there since I had it

Sorry about late reply , time difference

wannawagon

The simplest things in life are often the best

Great suggestion and it was the case, the light had been turned to constant - I feel like a dope

Many thanks, should have looked at it early

Many thanks to you and kombi

SunnyT

Glad it worked for you!!

I had that sensor short out on me once and you didn't list any of the symptoms, so I figured it had to be something that is easily overlooked.
Here are the symptoms if your sensor dies: 1) Headlights are always on 2) Interior ambient lighting is always on 3) Command screen is always in dark/night mode 4) Wipers will not work on automatic setting.
*Not sure of the associated codes*

All of these happen when the sensor dies since it controls it all.