Bi xenon headlights

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benm

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Jun 4, 2010
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I have a w212 eclass (pre facelift) with bi xenon lights. Recently notice the headlights were very poor and sure enough there was a message that right hand dipped beam faulty.
Checked relevant fuses and they were OK so naturally assumed the xenon lamp had blown after all they were originals and car now 11 years old.
Ordered new pair of xenon D1S lamps and spent a frustrating ½ hour fitting the right-side one only to find there was still no light . . . .

Read back actual values for right xenon headlight and supply voltage only 3.2v compared to 12v for left one. Further investigation traced the supply voltage to the thick yellow wire on the headlamp connector. Measuring directly at the connector also getting 3.2v although very occasionally flickering to 12v?
Am I correct in thinking the fault is not in the headlamp unit but what supplies it?
Where does the supply voltage come from?
 
Could be a ballast problem or earthing problem. Check and clean the earth point
 
I am measuring voltage using a good earth point.
The 3.2v is with the connector unplugged from the headlamp so before the ballast.
Does the headlamp supply voltage come from the front passenger SAM or via a relay?
 
Unfortunately my code reader does not read the front SAM. Anyway traced wires back from headlamp connector to SAM and they were good.
Then out of curiosity disconnected good lhd headlamp and interestingly voltage at pin 6 was now 3.3v. Thus I suspect the SAM must limit the voltage if it detects a fault?
I'm now fairly certain the problem lies with the rhd headlamp unit so tried another new bulb, admittedly not tested, and no difference. Is there a way to test the ballast?
Read back info on the xenon bulb and it has been operational for 110000 minutes, approx 2000hrs, which I believe is expected lifetime for the ballast?
 
I am measuring voltage using a good earth point.
The 3.2v is with the connector unplugged from the headlamp so before the ballast.
Does the headlamp supply voltage come from the front passenger SAM or via a relay?

Unfortunately my code reader does not read the front SAM. Anyway traced wires back from headlamp connector to SAM and they were good.
Then out of curiosity disconnected good lhd headlamp and interestingly voltage at pin 6 was now 3.3v. Thus I suspect the SAM must limit the voltage if it detects a fault?
I'm now fairly certain the problem lies with the rhd headlamp unit so tried another new bulb, admittedly not tested, and no difference. Is there a way to test the ballast?
Read back info on the xenon bulb and it has been operational for 110000 minutes, approx 2000hrs, which I believe is expected lifetime for the ballast?
Swap the working ballast over?

I needed to replace a ballast on my W211 with bi xenon lights last year.

I found the Hella part on eBay for around half the cost of the MB part (Hella make them for MB), if it is the ballast it will probably need coding.

I can look up the eBay seller if you need one 👍
 
I feel that it is the ballast as well, i had to replace one of mine last year, luckily my independent mechanic got me one from the US and it was 25% of the cost of one from MB UK .... all works well now.
Good luck. these things can be a pain to suss out sometimes
 
Thanks for the reply. I also think it is the ballast but will swap with the good side to confirm before ordering.
There is a huge range in price from around £50 up to £200+ for an OEM Hella ballast. Has anyone experience of using a cheaper ballast? Do they last and function correctly?
Incidentally I've read the ballast needs programmed to the car? Surely it just provides the correct voltage/current to drive the xenon lamp?
 
Thanks for the reply. I also think it is the ballast but will swap with the good side to confirm before ordering.
There is a huge range in price from around £50 up to £200+ for an OEM Hella ballast. Has anyone experience of using a cheaper ballast? Do they last and function correctly?
Incidentally I've read the ballast needs programmed to the car? Surely it just provides the correct voltage/current to drive the xenon lamp?
The (Hella) ballast I had fitted needed coding to the car (my W211 had the intelligent lighting system) so it wasn't simply plug and play in that case.
 
Today got round to swapping over the ballasts and the bad headlight now works so that is the issue.
An oem Hella ballast is circa £200 yet there are many cheaper makes available. Has anyone any positive experience of a different brand ballast or is it false economy?
 

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