Troubleshooting: Car Headlights Stop Working

July 6, 2017

2d5a6cb4bfd0a5a43620aaa5c7735faaFixing a problematic headlight on your car seems like a quick and easy job. And this can certainly be the case when dealing with a straightforward issue such as a burned out bulb. But headlight problems don’t stop there, so take a few minutes to read through this brief troubleshooting guide.

Problem: One headlight doesn’t work.

Possible causes: Burned-out or broken bulb.

When only one headlight fails, the most common cause is a burned out or broken bulb. A typical bulb may be good for up to 2000 hours of use; however, its lifespan will be shortened by factors such as excessive vibration (due to driving over rough roads), which can damage the filament inside the bulb and result in failure. Just replace the bulb as soon as possible.

Problem: Neither headlight works.

Possible causes: Faulty wiring or damaged fuse, headlight relay, or headlight module, resulting in low or no voltage to the bulbs.

Since there are many issues that may cause both headlights to fail at the same time, the best approach is to test each possibility one by one. Visually inspect the fuse, and replace it if you find that it is blown. If the problem is not the fuse, pull out the relay and shake it to determine if anything has come loose inside. Again, replace if necessary. If the fuse and relay are fine, check the wiring for visible damage. Finally, check that the module is getting power when the headlights are switched on. If it is, yet the bulbs still fail to light up, replace the module.

Problem: Headlights are dim or lose power when revving the engine.

Possible causes: Aging bulbs, dirty or discolored lenses, or aftermarket parts draining the electrical system.

Bulbs do lose brightness as they age, so if it’s been a while since you’ve replaced the bulbs try doing this first. If your headlights are still dim, inspect the lenses for dirt buildup or discoloration. Cleaning the lenses or using a headlight restoration/preserver kit will take care of that problem. Another possible cause of dim headlights is the use of a premium sound system or other aftermarket parts that place huge demands on the vehicle’s electrical system. Installing a high output alternator or an audio capacitor will take care of this issue.

A broken or burned out headlight is dangerous not only for yourself but for other drivers and pedestrians, so don’t let this problem linger any longer than necessary. Follow the troubleshooting guide here to identify the cause of the headlight failure, and then fix it as soon as possible.

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