Fix Headlight Bulb Issues
When headlights stop working, the cause of it is typically an electrical problem. If it is a physical issue with the bulbs, you can detect this by literally looking at the bulbs (e.g. check to see if the filament is broken in the halogen bulb) or by performing a test by swapping the working side with the non-working side. Determining what is needed is based on which bulbs have stopped working, under what circumstances, and whether the issue is with one side or both sides. Below are our cause and solution lists.
NOTE: Except for #1, we will skip mentioning replacing the bulb.
1) One headlight is out.
CAUSE: Most likely a burned-out bulb.
SOLUTION: Replace the bulb. We highly recommend replacing it in pairs because if one bulb went out, the other bulb would most likely go out soon. If replacing it with a new bulb still doesn't work, check the wiring or fuse. If this is just one side, we recommend checking the fuse and the wiring before replacing the bulb.
2) Both headlights are out.
CAUSE: An issue with power or ground.
SOLUTION: Since bulbs don't typically burn out at the same time, we would recommend checking power and ground. In most cases, both headlights simultaneously failing is a sign of a bad component like a relay, fuse, or module. If these are not the issue, replace them with new bulbs.
3) Low beams are fine, but high beams are not working.
CAUSE: An issue with the high beam switch or relay. In HID Xenon headlights, there is an assembly called, "Bi-Xenon headlight." This type of headlight uses a set of HID bulbs for both high and low beams. The headlight has a movable shutter that cuts off a portion of the light in a low beam position and opens up in a high beam position. If this mechanism fails, high beams will not turn on.
SOLUTION: Check the switch or relay. With the Bi-Xenon headlights, it is recommended to find a skilled mechanic or dealership.
4) Headlights work but the lights are dim.
CAUSE: Foggy lenses, a charging system issue, or installation error.
SOLUTION: Clean the lenses, or repair the charging system. foggy lenses will cut down the light output. The charging system issue is a bit more serious. One of the signs of this issue is the alternator. if the alternator is not providing enough power, the light would be dim and the alternator needs to be checked. Halogen or LED bulb mis-installation can cause dimming, but this happens more often with the HID Xenon bulb installation. With some vehicles, it may feel like the bulb went in correctly, but the bulb went in at a slight angle. When this happens, a portion of the light output will hit the back of the headlights and not produce the full light output.