Light Sensor - Drive To Workshop!
 

I'm wondering if anyone knows anything about this error. Nothing seems to not be not working, so this is more of an annoyance if anything.

It might be in my head, but this error seems to pop up if I haven't driven the car for a while (say 4+ days), or if it's a "cold" morning (0C or below). Thinking it was the battery voltage issue, I had it replaced at the dealership last week. Didn't solve the problem. They also did a "load test" on my car, with no problems. Battery and alternator are good.

There is NO CEL, and if I feel like it, I can simply stop and restart the car, and the error goes away every time.

Also not sure if this is related, but one of my bi-xenons is starting to do weird things too (flickering a couple of times before igniting, or not igniting at all). It started around the same time this error popped up. This error, however, is independent of the sensor error. I can get either error, or both, when starting the car after it hasn't been driven for a while.

One other thread mentions some kind of bulletin for bad wiring, but there's no link. Wondering if someone can enlighten me on this one. :)

I don't have power seats, so this is not the infamous power drain problem.

I have a feeling that your flickering Xenon is related. If you leave your lights in "auto" do they come on automatically when it get's dark?

Hi Glyn, in Canada we have DRL. The xenons turn on whenever the car is on, so I couldn't tell you. But it's always the same headlight. The other headlight is fine.

I'm with ya! so the auto light on sensor on the screen could have failed & you would not know without a message.

I'm not sure if it's the auto light sensor though. The way I tell is whether or not the instrument cluster lights up when it's dark outside or I drive into a tunnel. It seems to be behaving properly.

OK - check lamp & ignitor in the flickering Xenon.

If the xenon fails to ignite, I also get an error saying the bulb is out. This is intermittent though.

Is there a way to test the light sensor using a multimeter, or should I swap then cross my fingers?

Do bi-xenon igniters go bad in W203s? I know there was a bad batch much earlier on (replaced the passenger side as a result), but this one (driver's side) has been working fine for the last 7 years. This one (driver's side) is using the original form, with the black box and 2 rubber wires coming out.

I'm wondering if this is more in the direction of a loose harness somewhere.

The ignitors do fail - hence the kit Benz makes.

The light sensor is a diode so you need a diode tester.

Check all plugs on harness.

^ Thanks for the info Glyn. Just wondering if you can point me in the direction of where/how to test the light sensor. I'm assuming this is the one behind the central rear view mirror? Where does the other end go?

You are going to have to access the diode & unplug it. Here is a simple multimeter & sun/torch/laser pointer check.

http://www.repairfaq.org/sam/semitest.htm#sttpd

how old is your battery?? mine did this untill i got a new battery

I will say with your bix how old are the bulbs. I had an issue with mine that the bulbs arc got to big and they started to flicker. If the bulbs are really old then I would replace them but will say the reason my arc grew was because I had a bad ignitor.

**Update**

I picked up a 30kV igniter from eBay and replaced my driver's side igniter. All is well on the bi-xenon front. :D 1 problem down, 1 to go. Turns out that this exact igniter is shared across several makes including VW, Volvo, and Ford among others. The parts are WAY cheaper if you search using the "cheaper" makes for the exact same part. :smash:

I'm honestly out of ideas for the Light Sensor error. Anyone else have any ideas? I do notice that when this error happens, the car also seems to take 1s or so longer than a "regular" start, and that all the lights and radio dim during this second! :eek:

Strange update to this problem.

I disconnected all aftermarket accessories, and am still getting this weird error after not driving the car for a few days.

Today I parked the car for a few hours, then used the test mode and found the battery to be at 12.2V (it's within the normal range for a 12V battery I presume?), and started the car. The car flickered for a bit, then the voltage suddenly began to rise. 12, 13, 14, 15, 16, 17, 18.. I think at 19V the "Light Sensor, Visit Workshop!" error appeared, pulling me out of the voltage test screen. The entire spike lasted 1-2s at most, between the beginning of the rise and the error popping. I turned off the car, and started it again, and no errors showed up.

Glyn, any idea on this one? Again, the battery is new.

sounds like your battery is not holding the charge properly. under voltage causes the light sensor fault.

I'm pretty sure you have a problem with the voltage regulator on your alternator.. The voltage spikes cause all sorts of weird errors. You shouldn't see the voltage climb past ~14.2V at any point. Not long ago a guy on here with an 05 started having weird issues and after monitoring voltage he saw the spikes. Replaced the VR and all was good.

https://mbworld.org/forums/c-class-w...ompressor.html

Post #22 is where he catches it acting up.

slammer, if you want help with the alternator let me know. Sounds like it is easier to do when the passenger side wheel and wheel is removed, more access.

Sounds like for $60 and a couple hours work you'll have the last issue solved.

Ha, at least it didn't shut itself off, and tell you to walk to the workshop!
That would be funny. Someone should PS some bogus errors.
Like 'insert cash' or whatever..

Yeah, 19V ?
That aint right.
Replace the regulator.

I spoke with slammer last night, he's not convinced its the regulator yet I completely agree with you.

The regulator should prevent the 19V spikes slammer is seeing - yet I don't have enough information on how well these regulators work to prove that to him. I've read they are a mix of diodes and MOS internally which will limit voltage as well as switch power when thresholds exceeded in sub-second times. Thus if only using voltmeter it should be next to impossible to visually see any spikes.

Can anyone confirm that?

I can't confirm that, though I can confirm that voltage spikes will be visible in dyno mode with a malfunctioning voltage regulator. And that said voltage spikes will cause weird things to happen.

He's been plagued with this problem for a while now, he sees the voltage spikes, he sees the weird things happen.. the regulator is not expensive. If he doesn't want to take advice that's up to him.

Hey guys, thanks for the help.

I was hoping I'd be able to at least confirm the culprit before throwing a bunch of parts and cash at the car - already changed the battery at the dealer for nothing. Although the weird electrical stuff only happens within the first 3s of starting the car (and only after I've parked for at least a few hours), it does make logical sense. Might be a failed circuit that magically fixes itself as soon as it warms up from the current. I'll monitor the voltage for the next bit.

Would a failed VR also be responsible for my car using more current when parked? I suspect I may have a current drain as well. And no I don't have power seats or COMAND.

Can someone please post a link saying where to procure one of these things for $60? I can't find it for under $200. Thanks.

It doesn't seem a failed VR could do that since the VR regulates what the alternator puts out. Current drain would be something else, but I'm not sure they're related. The spikes in current aren't good for the electronics for sure, though.

Hey slammer, if your looking for a voltage regulator in the $60 range. I had this website saved for some reason. I have never dealt with them myself, I believe someone on this site had mentioned they had purchased a VR from them. There is another website that I have used for other parts, they sell the same VR for $129. Hope you get this issue solved soon. Good Luck.
http://www.americanenginesco.com/ser...c-class/Detail

slammer, I remember something I read from one of the DIYs: the brand of regulator has to match what you have in the car. People have tried different brands with bad results.

So first thing first, lets figure out what brand you have. I'm buying a telescoping mirror and magnet this weekend for a project on my new car, you could probably use it to read the brand off the back of the alternator/regulator.

I called the dealer with my VIN and he told me it's a Valeo. Does Valeo make anything decent? Seems like a ton of their stuff fail. :smash:

For the record I think the "must use same brand" is false. Someone here replaced his Valeo with a Bosch with no problems.

Thanks 1st lite for the tip. You just saved a bunch of us over $100 each! :y