Headlight problem
11-04-11, 07:24 PM
#1
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Headlight problem
Hey everyone, Recently my headlight has been randomly going out.. the bulb isnt burnt out because the light will come back on after i cut it on and off. but like i said it randomly shorts out from time to time. Any ideas?
11-04-11, 07:54 PM
#3
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BTW, what year is the car?
11-04-11, 09:28 PM
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I'm going through the EXACT SAME THING right now. It started happening the day I did an intense car wash on her. I'm guessing a little bit of moisture got on the ballast. Now I have to figure out how to take the head light out...not excited about this prospect :P
11-04-11, 09:51 PM
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From what I've heard you need to do some checks first-like swapping your head light back and forth from the right to left and see if it lights up on the opposite side just fine. If it does then it's probably the ballast. I've been told it's pretty inexpensive-we can try it together! As to how to do it, haven't figured that one out yet 
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11-04-11, 10:28 PM
#8
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I talked to the dealer, he suspects the bulbs, but I'm not 100% convinced. Although it's cheaper and simpler to start with the bulb. Mine go out randomly, left or right. Turning off the headlights, then on immediately, brings them back to life.
11-04-11, 10:52 PM
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I find that the dealer always seems to jump to the most expensive conclusion. The bulbs (for HID's) are way more expensive than the ballast. But yah, just troubleshoot the bulb-does anyone know of an existing forum link that explains how to swap out the bulbs? I know that may seem super simple to a lot of people here but I've never been much to work on a car before but I want to start with this one.
11-05-11, 08:10 AM
#10
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When a halogen headlight goes bad, the filament is broken or vaporized, and it simply fails to illuminate. That's not how Xenon headlights work.
HID lights don't have a filament. Instead, when you switch the lights on, the ignitor produces a very high voltage pulse to ionize the gas between the electrodes and establish an arc. Since the arc is essentially a short circuit, the ballast works to limit the current flowing through it.
The ionization voltage required to maintain the arc increases as the bulb heats up. It also increases over time as the lamps ages. A common failure mode of HID lamps is that they start normally, but as they heat up and the ionization voltage increases, the ballast is no longer able to supply enough power and the bulb goes out. Once they go out and cool down, the ionization voltage decreases such that the ballast is producing enough power again, but they don't relight since the ignitor only produces the high voltage pulse when you first turn on the lights. If you turn the lights off-and-on, the ignitor restrikes the arc, the bulb lights up, and the cycle repeats.
HID lights don't have a filament. Instead, when you switch the lights on, the ignitor produces a very high voltage pulse to ionize the gas between the electrodes and establish an arc. Since the arc is essentially a short circuit, the ballast works to limit the current flowing through it.
The ionization voltage required to maintain the arc increases as the bulb heats up. It also increases over time as the lamps ages. A common failure mode of HID lamps is that they start normally, but as they heat up and the ionization voltage increases, the ballast is no longer able to supply enough power and the bulb goes out. Once they go out and cool down, the ionization voltage decreases such that the ballast is producing enough power again, but they don't relight since the ignitor only produces the high voltage pulse when you first turn on the lights. If you turn the lights off-and-on, the ignitor restrikes the arc, the bulb lights up, and the cycle repeats.
11-05-11, 12:01 PM
#11
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I find that the dealer always seems to jump to the most expensive conclusion. The bulbs (for HID's) are way more expensive than the ballast. But yah, just troubleshoot the bulb-does anyone know of an existing forum link that explains how to swap out the bulbs? I know that may seem super simple to a lot of people here but I've never been much to work on a car before but I want to start with this one.
Do a search. Bulb replacement is very well documented on this forum.
11-05-11, 12:03 PM
#12
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The ionization voltage required to maintain the arc increases as the bulb heats up. It also increases over time as the lamps ages. A common failure mode of HID lamps is that they start normally, but as they heat up and the ionization voltage increases, the ballast is no longer able to supply enough power and the bulb goes out. Once they go out and cool down, the ionization voltage decreases such that the ballast is producing enough power again, but they don't relight since the ignitor only produces the high voltage pulse when you first turn on the lights. If you turn the lights off-and-on, the ignitor restrikes the arc, the bulb lights up, and the cycle repeats.
11-06-11, 06:39 AM
#14
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Either could those symptoms. More frequently it's a bad bulb that has aged to the extent the ionization voltage needed to sustain the arc at normal operating temperature is higher than the output of a properly functioning ballast. But it could also be a ballast that is producing enough voltage to sustain the arc in a hot bulb. Sango's suggestion of switching the bulbs to see whether the problem moves to the other side (in which case its the bulb) seems like a good idea.