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Had my headlight changed by my ex, now the car wouldn't start. Took the battery in and replaced it. Got the battery put in. Now it cranks but doesn't start. Hoping it something simple like my alarm won't allow it!

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    Usually if it's the security feature, the car won't even turn over, but all of the dash lights will come on. Oct 21 '16 at 10:04
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    Does it seem to crank at normal power, or does it crank slowly? There's nothing about changing the headlight that could cause this problem unless he REALLY screwed it up (i.e. replaced a spark plug with the bulb, and the bulb with a spark plug.) Oct 21 '16 at 18:30
  • Usually I roll my eyes when someone gives this generic of a solution, but my 03 E55 had the same issue and it was resolved after replacing the original spark plugs at 95k miles (mfg recc is 100k). Cheap and easy to try, anyway.
    – justinm410
    Dec 21 '16 at 1:03
  • Did the car stop starting immediately after the headlight was replaced?
    – dlu
    Dec 21 '16 at 1:04
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I had similar symptoms on an old ML320. It turned out the be the camshaft position sensor. Probably coincidental that it happened when you changed the battery, but an electrical trauma like arcing when the battery was connected could send enough transients into the electrical system to end the life of a near gone CPS.

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Does "cranks but won't turn over" mean the engine does turn over but never actually starts? I don't know about this particular model, but it's possible there's some kind of anti-theft setting that needs to be re-set. Perhaps your owners' manual discusses the anti-theft system, or you could call a local dealer or Mercedes specialist. Or, search the internet.

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