Stephen Durham

If I set my headlights to automatic they seem to come on randomly. On and off sometimes just once but other times they come on multiple times in row fairly quickly. It happens when it is perfectly sunny out no clouds and no shade on the car at all. Where is the sensor for the lights? I keep my car pretty clean, but maybe I am missing something.

I would prefer to leave it on auto but now I have it turned off and turn it on only if I drive at night.

-Stephen

pierrejoliat

The light sensor is in the windshield in front of the rear-view mirror, might want to pul codes to verify sensor is working correctly.

S-Prihadi

Blackout part of the front windshield is where the light and rain sensor resides. You cant see it.
Cali has stripped it once.
I think it reads infra red, hence it can be blackened out to hide its ugly shape and size.

I initially thought the small VISIBLE single camera (kind of ) on my car windshield was the light sensor, its is probably for the Auto High Beam option 628.

DFWdude

Interesting video. Shows how big the light sensor really is.

HOWEVER, be aware the part numbers shown are for a W203-W204 model (C-Class). The end segment of the video explains this.

So one should verify the correct part number for a W212. Could be the same, but maybe not.

Stephen Durham

I used my icarsoft scan tool and I got one that said: "An Implausible Signal From Switch - 'Exterior Illumination' Was Received" code is U141E00

So it looks like I need to replace the light sensor.

-Stephen

Stephen Durham

I pulled it off and the part number is A2048708826 on my car.

Stephen Durham

I pulled the sensor shown in the video and it is part number A2048708826 (~$80) but that is just listed as a rain sensor. The part number A0009057202 (Camera, Control Module, Ambient Light Sensor, Light Sensor, Multi-Purpose Camera) seems the more likely item but that is $900.

KEY08

Ouch

Left Coast Geek

that code is probably referring to the dashboard light switch rather than the sensors.

pierrejoliat

Well, I read that as a bad light switch, which is a known issue. I'm guessing, but it's likely the sensor is fine.

CaliBenzDriver

rain sensor

disassembly

solderless pins: good until flaky....

Isn't there a mushroom style plastic sensor on the dashboard or is it this rain sensor that serves as light sensor too??

Very easy to open and snap back after soldering if you decide doing so...roundtrip under 60mn
✌️

konigstiger

Utilizes multifunction camera. If interior/exterior windshield and camera lens is clean you will need to have someone pull codes using MB diagnostics may simply need re-calibration.

Stephen Durham

I did a search for bad headlight switch in the forums and some of them had the same issue with the "A" setting. I'll replace the switch and check the solder on the sensor to see if that resolves the issue. If not I will take it to the dealer to have them test the multi-function camera as I don't think my iCarsoft can do that. I definitely do not have the tools to recalibrate the camera.

In regards to the solder issue are you looking at the three pins that push into the board for the plug/connection? Those do not look like they have solder but everything else appears fine.

It looks like the switch assembly is part # 212-905-19-00-9107

Arrie

Does your scanner show the error code under the multifunction camera?

CaliBenzDriver

I guess you need to do a bit of troubleshooting around that issue to figure if the sensor is mad, network or controller got disrupted

Stephen Durham

The error was listed under the Driver side SAM.

CaliBenzDriver

came across this ...

The daylight sensing appears to be done by rain sensor unit I mentioned above. Check for loose pins, hope this helps.

This unit may -or may not be your bad guy. Could be your light switch had it or a loose GND somewhere.

Stephen Durham

Thanks for the schematic. I pulled it out last night and I am going to try to solder the pins to see if that fixes it. After pulling it out when I turned on the car it said that the automatic light functionality was inoperable (or something along those lines). So I am fairly certain it is that sensor.

CaliBenzDriver

While you have the small sensor dismantled, take couple close up pics to see if there is evidence of any oxidation buildup between traces on either sides -or damaged capacitors

Schematic shows "OCP" is acting as the CAN gateway for the LIN "Rain/LT" sensor.

The condition that causes a system to disfunction is any body best guess. What is in charge of powering the lights On/Off :

• the Rain sensor,
• the F-SAM,
• the light selector switch,

All of these modules have ability to mess up the headlights, not to mention GND screws.


Someone who has been fixing these W21X cars for 10 years will practically know the special ways they fail without tracing any schematic.

Stephen Durham

Here are some photos of the sensor internals.

CaliBenzDriver

Your sensor shows no obvious oxidation, fat caps, missing or blackened solders... 👍


photo-sensors + pins

While you're in there... wipe the photo-sensors and optical lens clean and fairly dust-free.

I'd solder the 3x connector pins to rule them out easily from your short list -

Stephen Durham

I cleaned it and put some solder on the three pins and put it back in the car. So far so good, nothing came up in a scan and when I drove this morning the lights did not randomly come on. I guess I will watch it for a bit and see what happens.

Thanks for all the assistance.

S-Prihadi

Sweet...I hope this stay fix for a long time.
I love happy ending and more so if ZERO PARTS.
So until proven otherwise, we can call this BAD-INTERMITTENT-CONTACT ..........
Good thing Cali started preventive maintenance on his rain-light sensor + other modules few weeks ago.

CaliBenzDriver

Above all, thanks to you for making this at all possible.

You take us on deep dives into many research topics where we can spot carefully hidden money pits...
I am a dive buddy or a wing man - I don't mean chicken wings, we don't chicken out to strip things out

Glad I could empower a smart owner to enjoy his Benz without service aggravations. That being said, your homework is to go clean your painted GND posts front to back if you will. No skills needed.

Knock on wood and enjoy...

pierrejoliat

Great job Cali.