Headlights are essential safety features in cars, especially during night driving. Most people do not know there are differences between high-beam and low-beam headlights. A high beam cannot substitute for a low beam. In the same manner, a low beam cannot substitute for a high beam.
The headlights can fail in different ways. Sometimes, a headlight bulb can fail and still light. A good example is when one of the low-beam headlights is not working. Auto manufacturers wire low-beam and high-beam headlights on different circuits. This way, a low beam on one side can fail while the high beam on that side remains functional.
This article will explain why one headlight is not working, but the high beam is. You’ll also learn how to fix the underlying issues. But first, let’s examine the probable causes.
What causes one Low-beam Headlight not to work?
There are several causes of a low beam headlight not working on one side. A blown fuse is one of the most common headlight issues I have fixed in my garage. Here are my experiences with what I found to be the possible causes. But before we go ahead, always check the headlight fuses before narrowing down to other causes.
Burnt headlight bulbs
If the left or right headlight is not working, you may have a burnt-out bulb. As explained earlier, headlamp bulbs can fail in several ways. Only the high beam or low beam can fail. If one side headlight won’t work on a low beam, you likely have a failed bulb.
But if both low-beam headlights stopped working, the bulbs are most likely not the culprit. This is because it is quite rare for both bulbs to fail at the same time.
Bad relay
Another likely reason why headlights won’t work on low beams is a lousy headlight relay. There’s a relay inside the fuse box that works in harmony with the switch on the steering column or dashboard to control the headlights.
The relay has a solenoid inside that can fail and require replacement over time. If this is the root cause, the low-beam headlight may not light until you replace the bad relay.
Lousy multifunction switch
The multifunction switch in the vehicle can fail over time. This switch controls several functions, like windshield wipers, turn signals, single-switch control, headlights, and more.
The multifunction switch can fail and prevent one of these features from functioning as intended. However, it is essential to note that this is a possible but unlikely reason why one LED headlight is not working.
Blown fuse
As explained earlier, if you’re asking what the most probable causes are of one low beam headlight not working? You should think of a blown fuse. A blown fuse is the most common reason one side’s low-beam headlights fail while the other side works.
Automakers protect every electrical system component in a car with fuses. Most fuses in vehicles have a tiny metal strip running across two terminals. The small metal strip conducts electric current between the terminals and is designed to melt when there’s a power surge in the system.
Once the metal strip melts, it’ll prevent electric current from traveling to the system it is protecting. Of course, this will prevent that component from working.
How do you fix Low-Beam Headlights not working?
You’ve seen the probable causes of one low beam not working, but how do you fix low beam headlights not working? Since there are several causes, there are several ways to fix them. Firstly, you have to track the root cause of the problem.
Replace the blown fuse
It is essential to always start the diagnosis from the most common probable causes. For example, if one of your headlights’ low beams is not working, you need to locate the fuse boxes and test the fuses responsible for the headlights.
Cars usually have two fuse boxes—one underneath the steering wheel and the other in the engine bay. In most cars, manufacturers place the headlight fuses in the fuse box under the steering wheel. Therefore, you should start your diagnosis from this place.
Open the fuse box and locate the headlight fuses following the diagram on the fuse box cover. You will likely see three to four different fuses for the headlamps. Test them with a test light and ensure they are working correctly. If any of them is faulty, replace it with another fuse of the same amperage.
Inspect and replace bad relays
If all the fuses are in good condition, you have to narrow down to the headlight relays. Check them and ensure they are working correctly. If the relays are faulty, replace them.
Change the dead bulb
As explained earlier, bulbs can die in several ways. A bulb’s low beam can fail while the high beam is still working. Similarly, the high beam can fail while the low beam is still working.
If one side of the headlight is lit in both low and high beams, move the bulb to the other side of the lamp and see if it works there. If that bulb works on both sides, you have a dead bulb that needs replacement.
It’s also possible for one headlight not to work after replacing the bulbs. It usually indicates an incorrect installation or a manufacturing defect. Therefore, ensure that you have installed the bulb correctly and that it is in good condition before moving on to other feasible solutions.
Check and replace the multifunction switch.
As reiterated above, the turn signal, wiper blades, or headlights will stop working if the multifunction switch fails. Therefore, if one or more of these components stop working, the multifunction switch can be the culprit.
If all the potential solutions above prove abortive, try changing the multifunction switch. However, this should be the last thing you look into, as it is less likely to be the root cause. Check out this well-detailed article where I explained how to diagnose headlight bulb problems.
Frequently Asked Questions – FAQs
Q: Why is my left low beam not working?
Something is wrong if the right or left low beam is not working. It could be the multifunction switch, one of the headlight fuses, the headlight switch, the headlight relay, or the dimmer switch. The common and easiest fix among them is a blown fuse.
If a blown fuse is the root cause, you can fix the problem yourself for $10 to $15. But kindly note that the repair cost will be more if you have a certified technician fix it.
Q: Can you drive with one low beam out?
A non-functioning low-beam headlight does not prevent you from driving. This, however, does not mean you should run without a low beam. The fundamental laws in most states require you to drive with both lights from night till morning.
The law also states that all lights in a car should be in good working condition. The corps can pull you over and issue you a ticket. So, it’s essential to track and rectify the underlying issues.
Q: How much does it cost to fix a low beam?
The cost of fixing a low-beam light depends on the cause of the problem, your car model, and the technician performing the repair. If the leading cause is a blown fuse, budget $10-$15 if you’re replacing it yourself. The money is to get a replacement fuse of the same amperage.
But if the root cause is a defective headlight bulb, budget to spend around $75 to $100 for the replacement. The parts should cost $25 to $75, while the service charge will be about $50 to $75. Kindly note that this is just an estimate. Therefore, the exact price can be lower or higher.
Q: Should you replace both low beams at once?
It is recommended to replace both bulbs at the same time, even if one is still working. This is because replacing one bulb will prevent the headlights from outputting the same light quality. Night driving has its drawbacks. So do not add to it by driving in uneven lighting conditions.
Q: Does AutoZone replace low beams?
AutoZone is not a mechanic’s garage. With that in mind, they do not provide mechanic services such as wheel alignment, balancing, brake repairs, headlight replacement, etc. However, AutoZone will guide you through replacing headlights and provide all the tools and parts you need for the job.
If the cause of the low beam not working issues emanates from faulty headlights, they can help you replace the bulb only if the bulb replacement does not affect any other system components.
Q: How long should low beams last?
Both low and high beams are designed to fade out at the same time. So if you’re asking how long does a headlight last? A standard headlight bulb should last five years before needing replacement. However, most system components fade out earlier before their expected lifespan. This means your low and high beams can last up to five years and can die earlier than that.
Final Words
This article has outlined the causes and how to fix one low-beam headlight not working. However, if this issue happens after replacing a headlight, the leading cause may be different. Check out this article where I explained why one headlight is not working after replacing bulbs.
In summary, a blown fuse is the most prevalent cause, and you should start your diagnosis here. If all the fuses are good, narrow down to the bulbs before heading to the relays.
