DIY

Why are My Headlights Flickering?

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Driving with a flickering headlight can create unsafe conditions on the road as they can create distractions not only for you but for other drivers as well.

If you’re wondering why your headlights and dash lights flicker when your car is running, you’re reading the right article. There are many reasons why your headlights may be flickering.

What Causes Flickering Headlights?

Generally, flickering headlights are caused by either a faulty bulb or a problem within the headlight circuit.

replacing car headlight bulb
Flickering headlights are usually caused by a broken lightbulb.

If your headlight keeps going out while driving, here are the most common reasons why:

Failing Bulb

If you have halogen bulbs, the flickering may be caused by the filaments becoming damaged or worn out.

Most often, this is a tell-tale sign that your headlight bulb is nearing the end of its life.

There are different types of headlight bulbs, each with their own expected lifespan. Halogen headlights, which typically burn hot, usually have a shorter service life and will fail faster than others. If you have an older vehicle or even a newer, mid-priced model, you likely have halogen bulbs in your headlight assembly.

Higher-end vehicle models often come equipped with either light-emitting diodes (LEDs) or high-intensity discharge (HID) lights, which tend to last much longer.

Headlight Circuit Problem

Flickering headlights may also be caused by a circuit problem. For example, the issue can point to damaged wiring or a poor connection. A bad headlight switch or relay could also be to blame.

The headlight switch assembly on older vehicles includes a built-in circuit breaker, and when a short circuit occurs, it can cause the headlights to flicker.

This is why flickering headlights used to be common with older models.

Weak Battery

Your car battery will usually give you signs when it is nearing the end of its life—one of them may be flickering headlights.

A weak battery may not give out enough power for your headlights, causing them to go dim or flicker.

Generally, car batteries can last around three to five years. However, there are several factors that can affect your battery’s lifespan, such as your vehicle’s condition, your driving habits, or the weather conditions where you live.

If there is nothing wrong with your bulbs or headlight circuit, then you may want to check the battery for issues. Who knows? Maybe it’s time for a car battery replacement.

a typical car battery
A weak car battery can cause dim headlights.

Failing Alternator

An issue with the alternator (or the voltage regulator, which is often located inside the alternator) can cause the headlights to flicker. Such charging system problems may lead to inconsistent current output, which can cause your headlights to flicker.

If this component is to blame, you will likely observe a few other common symptoms that point to a bad alternator.

It is important to diagnose the problem right away, so you or your mechanic can fix your flickering headlights as soon as possible. If you do not have the technical know-how or DIY skills to resolve the issue, it is best to leave this job to a professional.

Diagnosing Your Headlights

As discussed previously, flickering headlights can be caused by one of several potential causes. Once you’ve ruled out the battery and the alternator, here are other ways to diagnose your flickering headlight problem:

Visual Inspection

The first step is to perform a visual inspection. Look for issues, such as:

Using a Scan Tool

If you have the DIY skill and a factory or factory-level scan tool, you can diagnose a broken headlight by following these steps:

  1. Using your scan tool, turn your headlights on using the bi-directional command. If they do turn on, this means the problem does not lie in your headlight circuit. The problem is most likely associated with the control input to the specific controller that controls the headlight.
  2. Pinpoint the location of the open circuit by checking the voltage at different parts using the schematic for the headlight circuit. For this step, make sure to always follow your repair manual.

    If your headlights appear brighter than normal, the problem may be related to a high battery voltage. Check the charging system voltage and make sure that it is less than 15.5 volts, which is the standard for most vehicles. You can check the service information to find out the exact specification.

    If your headlights are dimmer than usual, this can be a sign that there is excessive circuit resistance, such as a loose electrical connection, a corroded socket, or poor electrical ground connection.
dim car headlights
You can diagnose your car headlights by doing a visual inspection or using a scan tool.

Flickering headlights can cause accidents on the road. If you notice that your headlights are not working properly, do not waste time and address the issue right away. You and your passengers’ safety should always come first.

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CarParts.com

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In the Garage with CarParts.com is an online blog dedicated to bringing DIYers and devoted car enthusiasts up to date with topical automotive news and lifestyle content. Our writers live and breathe automotive, taking the guess work out of car repairs with how-to content that helps owners get back on the road and keep driving.

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