9 Reasons Your High Beam Headlights Are Not Working
High beam headlights are an absolute must for superior night vision and driving safety.
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Required by law around the world, low beam and high beam headlights help you see and be seen, in all kinds of weather and at any hour of the day. Low beams are the bare minimum, for safety’s sake, but high beams are an absolute must for night driving over 25 mph. For most vehicles, headlights are a basic electrical system, controlled by switches and relays to turn them on and off. If your high beams stop working, here are nine of the most-common causes.
Headlight bulbs are available in every autoparts store and many other stores, so it should be easy to find what you need. Check your owner’s manual to be sure which kind of high beam bulb you need and get familiar with the fuse box in case the high beams stop working. Finally, practice using a digital multimeter so you can rule out electrical problems before replacing other components.
Blown Headlight Bulb
This is the most common cause of a single high beam headlight not working, but isn’t common if both high beams aren’t working, because it’s highly unlikely that both bulbs would blow at the same time. Headlight bulbs have a limited lifespan — 450 to 1,000 hours — so they’ll eventually burn out.
Blown High Beam Fuse
A fuse protects the wiring from damage, in case too much current is being drawn through the high beam circuit. The fuse will blow if there’s a short circuit, but it might also blow if an accessory is drawing off it or if the bulb is the incorrect wattage. Repeated blown fuses require more diagnosis to pinpoint excessive current.
Faulty High Beam Relay
The headlight switch usually doesn’t control the headlight bulbs directly, but through one or more relays. The headlight switch powers a relay, which powers the headlight bulb. This protects the headlight switch from the high current used by the high beam headlights.
Failing HID Generator
In the case of high-intensity discharge (HID) headlights, or Xenon headlights, there’s an additional component. To get the xenon and salts to plasma state, the HID generator bumps the voltage up to 30,000 V, then stabilizes around 90 V when the bulb is in operation. If the generator fails, the bulb won’t light.
The most common short circuit is caused by damaged wiring, perhaps due to a crash, damaged connector, or poor aftermarket accessory installation practices. Broken wiring simply stops current flow, while chafed or damaged wiring might send it elsewhere, to ground or to another circuit. Loose or corroded connections, especially at the headlight bulb, can overheat and melt.
Failing Headlight Switch
A failing headlight switch is uncommon, because the headlight switch is inside the vehicle and well-protected. Still, if you drive a lot, especially at night when you must constantly change between high beams and low beams, you might wear out the headlight switch.
If the high beams function but don’t seem to light your way, especially if you drive an older vehicle with polycarbonate headlight lenses, your car may be a victim of headlight fogging. This isn’t simply scuffing, but an actual chemical change from polycarbonate’s exposure to solar ultraviolet light and caustic exhaust emissions. The diffused light doesn’t project very well, making it hard to see, even when your high beams are on.
Incorrect Headlight Bulb
On some vehicles, particularly those with HID headlights or solid-state circuit protection (Zener diodes or high beam circuit breakers) installing the wrong bulb might result in intermittent headlight operation or no high beams at all. The wrong bulb might not ignite at the right voltage or draw too much current for the circuit protection’s design.
“Didn’t I just replace that high beam bulb?” you say as the high beams fail yet again. This can happen if greasy fingerprints cause part of the bulb to heat unevenly, breaking it. If you have multiple headlight bulb failures, make sure you are especially clean when doing the job. If at all possible, don’t touch the glass portion of the bulb at all. If necessary, handle the bulb with clean latex or nitrile gloves. Finally, if the bulb is dirty, clean it with a fresh alcohol pad before installation.
Fixing Your High Beam Headlights
Headlight bulbs are available in every auto parts store, so it should be easy to find what you need. Check your owner’s manual to be sure which kind of high beam bulb you need and get familiar with the fuse box in case the high beams stop working. Finally, practice using a digital multimeter so you can rule out electrical problems before replacing other components.