How To Diagnose Headlight Problem – All You Need To Know

Your car headlights are not built with complex technology, but they can fail in different ways. Therefore, once you notice that your headlight has failed, you need to diagnose the problem to know the kind of failure you’re dealing with.

This article will explain how to diagnose headlight problems to help you track and fix the root cause. The diagnosing process you’ll follow depends on the key cause of the failure. That said, it is essential to start by examining the type of failure you have. Is the high beam still working? Are both of the lights still working? But first, let’s start by a briefing on the most common headlight problems.

how to troubleshoot headlight problems

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Most common headlight problems

As suggested above, headlights are not built with complex technology. With this in mind, their common problems lie with electrical issues or the bulbs themselves. You need to note the type of issues you encountered for a more straightforward diagnosis to know exactly how to track it.

The most common headlight problems you’ll likely encounter are as follows;

One headlight is not working. This usually means you have a burnt bulb. Headlight bulbs usually fail one by one, which explains why you should check the bulbs whenever one fails. However, bad connectors or electrical issues can be the culprit.

Both headlights are not working. This means the bulbs are dead, or you have power or ground issues. Most times, both bulbs do not fail at the same time. Therefore, before blaming the bulbs, check the system for bad modules, relays, fuses, and the wiring harness.

One highlight out, but high beams work. Sometimes, the low beams will work while the high beam won’t, or vice versa. It could mean you have a failing bulb, or the high or low beam relay or switch is bad. If only one bulb fails to work on a low or high beam, the bulb is failing. Sometimes, a bulb with high or low beam issues emanates from that beam switch or relay.

The headlights are working, but they are dim. In this case, the car likely has charging issues, worn-out bulbs, or foggy lenses. If the headlights are constantly dim, you likely have bad bulbs or foggy lenses. But if the headlights seem dim in certain situations, charging issues is likely the culprit.

Other problems are caused by relay or wiring issues, bad switches, and bad bulbs.

how to diagnose hid headlights

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How to diagnose and fix headlight problems?

Most vehicle headlights feature three main system components that work in harmony. These include the headlight bulbs, the fuse (this protects the bulbs from damage through a power surge), and the wiring harness (this transmits electric flow to the headlight bulbs). The wiring harness includes the wires and the connectors.

Therefore, the diagnosing and fixing procedures revolve around these areas. First, let’s look at how to diagnose headlight problems in simplified steps.

Step 1: Check which bulb is working

Open the car and turn on the headlights. Check which of the headlight is working. Remember to switch the lights between low and high beams to ensure the problem is not occurring when you turn on the lights to a certain beam. After that, open the hood and move to the next step.

Step 2: Check the wiring harness

With the hood open, lose the negative battery cable and remove it from the battery terminal. Next, trace the wiring harness at the back of the headlamp and disconnect it. Finally, inspect and ensure the wiring harness contacts are clean. Look for corroding and discoloration and clean them as necessary.

If the top layer of the bulb or the connector is corroded, clean them properly. Spread dielectric grease on the surface before reconnection to prevent the connectors from rusting in the nearest future. Next, reconnect the disconnected battery cable and turn on the headlights if this doesn’t fix the underlying problem, head on to the next step.

Step 3: Replace dead bulbs

If step one above proves that one of the bulbs is not working correctly, the best thing to do is to replace the defective bulb and see if that resolves the problem. Move to the next step if this doesn’t fix the underlying issues.

Step 4: Inspect the fuse

Open the fuse box in the engine bay and locate the fuse that controls the headlight circuits and see if the fuse is working correctly. If you can’t find the fuse in the engine bay, check the fuse box in the cabin underneath the steering wheel. Follow the diagram on the fuse box cover to identify the fuse responsible for the headlights.

I published an article that explains what a blown 40 amps fuse looks like. Check that article to know what a blown a fuse looks like to aid your inspection.

Step 5: Test the wiring harness

The common causes are described and dealt with by now – diagnosing process and procedures for headlight issues. However, if none of the above fixes can sort the problem out, you may have issues with the wiring harness.

To test the wiring harness:

  • Unplug the wiring harness from the defective headlight.
  • Grab a voltmeter and connect the black probe to the negative battery terminal.
  • Connect the red probe to the positive wire on the headlight wiring harness.

There should be an electric current coming from the positive wiring harness. If there’s no electric current traveling through the lines, visually inspect the wiring cables back to the fuse box. If you find any tear, open, or shorted wire, fix it. That should resolve the underlying problem.

Read: How to Make Headlights Brighter in Minutes

Frequently Asked Questions – FAQs

What is the most common reason for a headlight failure?

I have outlined the various causes of headlight failure; however, the most common causes are dead bulbs and blown fuses. Other causes are bad switch and relay issues or wiring harness issues. A bad switch can cause both low-beam headlights to stop working. It can also cause both high-beam headlights to malfunction.

Is it better to restore the headlights or buy new ones?

Buying new headlights is better than restoring old headlamps. Here’s why I said so; restorations deal with cleaning the lens while getting new headlights to replace the entire unit. Every part of the headlamps comes new, meaning a brighter view and no need to acquire a new set of bulbs. However, if you’re on a budget now, you can choose to restore the lamps instead of buying a new one. But restoring headlights cannot be a permanent solution to such a crucial issue.

How do you find a short in headlights?

An electrical short is a low-resistance connection between two conductors transmitting electric juice to a circuit. For example, an electrical short happens when there’s a dimmer switch, headlight switch, headlight relay, or wiring fault.

The best way to find a short on the headlight is to test the headlights with a light tester and see if it is transmitting light. After that, visually inspect the wires for frayed, damaged, or burnt areas. Fix damages as needed to resolve the pending issues.

Is fixing a headlight easy?

Replacing a headlight is easy. Most light-emitting-diode (LED) and halogen high-intensity-discharge (HID) are easy to replace. All you need to do is remove the clips holding the headlamp and disconnect the dead bulb from the socket. Then, install the new bulbs and close the headlamp with the clips holding it in place.

Can AutoZone replace my headlight?

Since Autozone is home to several auto spare parts, it is safe to ask if they can fix headlight problems with Honda CRV or any car model. There’s no direct answer to this question. But first, you need to understand that Autozone is not a mechanic shop. They specialize in selling auto spare parts.

They can provide the correct bulbs for your headlights and also give you directives on how to replace them. However, Autozone can also help you replace the headlights if it doesn’t involve taking off other car components.

Final Words

I have outlined the common causes of headlight failure and how to diagnose headlight problems. The easiest way to detect if you have a dead bulb is to remove the bulb that is not working and replace it with a functioning one. If the bulb lights, you know that you have a dead bulb that needs replacement.

The diagnosing and repair procedure is simple. However, you have to take precautionary measures once you detect the root cause is from the wiring harness. If you don’t trust your gut, have an experienced technician rectify the issues to avoid frying the wires.

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Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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