Piston Slap: Going Ballast-ic on Bi-Xenons?

Confused in South Bend writes: Hi, Sajeev…. I am the owner of 2003 M-B C240 base, with the Bi-Xenon headlights. Recently, one of the headlights has developed an issue….in cold weather, it does not work. Went to my German car specialist, who wasn't so special on this issue.  No problem, he said, replace the bulb.  $160 later, still had the problem.  OK, negotiated for him to give me a credit on the next fix. Researched on the web, purchased a used Ballast.  Mr. German car specialist looked at the part, scratched his head and said, "I don't know what this part is." Mercedes dealer says, spend about $900 for an entirely new headlight assembly. I know that Mercedes engineers think money grows on trees….but $900 to fix a balky headlight?  Come on… I want to get this fixed….my question, is replacing the ballast the way to go?  Or must I render to Stuttgart…..? Sajeev answers: When one HID headlight goes out, the ballast and/or the bulb is usually the problem.  And I would never just buy a new HID bulb just to take a stab at the problem, especially when we know the quality of electronic components in German vehicles of this vintage. Who knows, maybe there's a lighting control module mounted elsewhere that we non-German-techie people don't know about!  This is what specialty shops are supposed to do for us! But, unfortunate diagnosis aside, I still think the smart money is on a bad ballast. A visual inspection of the bulb is necessary, and the ballast is first tested by checking for power to the ballast itself.  If you got nothing there, bigger problems away from the headlight assembly are in your future. If not, get the ballast tested and repaired/replaced. I am by no means a lighting guru, but from what I see via Googling, you can't test a ballast with your garden variety multimeter. A specific tool is needed. You made the classic mistake: buying a part and hoping for the best.  Find someone who knows what they are doing to test and verify the actual problem. From the sound of it, you need a new German Specialist. Send your queries to sajeev@thetruthaboutcars.com . Spare no details and ask for a speedy resolution if you're in a hurry.     from The Truth About Cars http://www.thetruthaboutcars.com

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