CLK55 2003 W209 - Light Sensor Visit Workshop Malfunction & Sensor Revisions


New Member
Feb 5, 2016
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Your Mercedes
CLK55 AMG W209
Hi All,

My wife came home last week after a trip in our 2003 CLK55 with a nice little present for me to fix.
The dash showed "Light sensor - Visit Workshop" error....great!.

I have read all the posts on various forums across the web regarding this error to try and resolve issue.

First I started with checking for low voltage seeing as we have had cold weather and we don't use the car much, the battery is only 6 months old genuine MB 100AH, never had an issue with slow starting ETC but charged it fully anyway. Still get error message after every startup. The alternator regulator was replaced last year also and I see a healthy 14.4v when engine is running.

I decided to buy a replacement light/rain sensor from my local MB dealer, £53 +vat and hope this resolved the issue. I was told there have been many revisions of this part and I now have the latest part.

I have now installed the light/rain sensor on the top of windscreen behind the RVM. The error message has stopped alarming so it appears this sensor was faulty.....however the car now thinks its permanently dark as the command unit screen is always dark and headlights always come on during daylight when switched to Auto.

I have been informed that the new sensor needs to be coded to the car via STAR and correct windscreen type to be entered, Is this correct?, I have my car booked in next week at my Local Indie who has STAR facilities. Just looking for any advice on these sensors.

Also the new replacement sensor now has an S-Class part number A221 870 00 92 and is missing the grey long resister type device which I have learnt is a heating element? My original part A209 820 07 26 has this. I am worried I am missing some functionality of this unit although MB parts confirmed this as the correct and only replacement and is shared between the CLK and S-Class.

These are the revisions I have found searching Ebay
A209 820 07 26 - Part build date 05/2002 -> (my original part)
A209 820 24 26 - 04/2003 ->
A209 820 31 26 - 07/2004 ->
A209 820 49 26 - 10/2005 Heating element now removed from sensor
Now changed to S-Class part number
A221 870 28 26
A221 870 88 26
A221 870 00 92 - Current part number for CLK and S-Class

So looking at sensor revisions it appears the heating element was removed during 2005 around the time of the facelift CLK.

Do I need the heating element in this sensor? should I just buy a replacement like for like part off ebay with the heating element and take a chance it still works correctly?. Why so many revisions? are the later versions better?, why was the heating element removed and does it need coding via STAR to work correctly again?

Any info on this very much appreciated



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