“Light sensor, drive to workshop”

[clk320x]

Just had this while driving in the morning on my e320cdi wagon...

Could it be something as simple as dirt on the sensor? I hope so lol

Abs

 

[KillerHERTZ]

Its the little sensor on the bonnet (tiny dome) try unplugging it, giving connectors a clear and re-attaching it.

 

[clk320x]

Its the little sensor on the bonnet (tiny dome) try unplugging it, giving connectors a clear and re-attaching it.

Thank you Karl,I thought there is one also behind the RVM? or is this for the wipers?

I’m thinking about washing it as it’s quite dirty now.. hoping it’s something simple but is it ever with me

 

[Stratman]

I had this appear a couple of times recently, coinciding with a difficult start. A combination of cold weather and short journeys gradually reduced the battery voltage to the point it could just about turn over and start the engine. The actual voltage while the starter motor was churning must have been low enough to trigger an error somewhere, with the low light sensor the first to crack.

I bought a CTEK MXS 5 smart charger to keep it topped up and it's been fine since.

 

[BTB 500]

The actual voltage while the starter motor was churning must have been low enough to trigger an error somewhere, with the low light sensor the first to crack.

I had something similar on my SL which threw up sensor errors on both windows and roll bar after just starting once. Had to get them erased via STAR in the end (the roof was disabled till I did this). I also bought a maintenance charger

 

[Codger49]

Thought the tiny dome on the bonnet is the sun sensor for adjusting a/c outputs to cope with solar gain through the windows.

Lighting is influenced by the combined rain/light sensor mounted on the windscreen behind the rear view mirror.

 

[clk320x]

Update:

Some kind members have given me the p/n

New the sensor is £80.40, the latest revised part is £20 on eBay used from a 2009 car. I’d normally say New new new, but maybe a used sensor would suffice as it’s not a common failure ?

 

[wu56Shoozz]

Not that old chestnut again..

Just pay the £20 and be done... jeez yer not Scottish or related to me are ya Lols (Long pockets short arms ha ha)

 

[markjay]

AFAIK the 'Light and Rain Sensor' and the 'Sun Sensor' are two different things.

The first is behind the RVM and controls equipment such as the wipers and the auto headlamps etc.

The latter is on the dashboard and it is for the climate control system.

 

[clk320x]

Hi again guys,

So I have got a replacement rain and light sensor on order.

Is this something I can swap out myself or does it need some kind of star calibration?

Thanks
Abs

 

[MancMike]

Aren't they full of fluid between the sensor and the glass, to make that air boundary "disappear"?

Mine has an air bubble in it from my windscreen being replaced...

 

[clk320x]

Aren't they full of fluid between the sensor and the glass, to make that air boundary "disappear"?

Mine has an air bubble in it from my windscreen being replaced...

No don’t think so Mike? The WIS instructions don’t mention anything like that. Seems to be just a clip off, disconnect the electrical plug, and clip on the new one.

 

[MancMike]

It definitely does, it's how rain sensors work. They fire infrared light, and it reflects back. When a rain drop lands on the sensor, the infrared light doesn't bounce back, it gets scattered by the rain drop.

Without the fluid between the sensor and the glass it wouldn't work. Maybe the fluid is inside and there's a gel/rubber contact patch so that there's no air gap, instead.

See:

With air bubbles in;

Mine looks similar, I'll get a pic later.

 

[whitenemesis]

No fluid in the S203 '05 rain/light sensor. I retrofitted one to my car and had to replace the windscreen as it has the lenses bonded to the inside of the screen. The sensor then just clips on over the top of the lenses.

 

[clk320x]

No fluid in the S203 '05 rain/light sensor. I retrofitted one to my car and had to replace the windscreen as it has the lenses bonded to the inside of the screen. The sensor then just clips on over the top of the lenses.

Excellent, thank you. Do you know if I will need Star coding following the replacement?

Thanks

 

[whitenemesis]

You shouldn't do, usually only requires re-calibration if the screen is replaced. If you find operation is erratic or sluggish then a session on STAR might be needed.

 

[clk320x]

You shouldn't do, usually only requires re-calibration if the screen is replaced. If you find operation is erratic or sluggish then a session on STAR might be needed.

Thanks very much I shall try and report back

 

[clk320x]

Replaced today, wipers & auto-lights working a treat. Star was not needed.
Simple unclip old one, fit new one. Lenses bonded to inside of screen as Pete notes above.

Thanks everyone.
Abs