How to Fix a Car Horn That Won't Stop Honking

Car steering wheel
When your horn won't stop honking, pushing it again may unstick a bad switch, but that won't always fix the problem. nubumbim/iStock

Some technology is so basic, so ingrained into daily life, that you just expect it to work. When something like a car horn, that you probably don’t even think about until the exact moment you need it, malfunctions, it can quickly become a nightmare scenario. And despite being so basic, there are a number of ways that a car horn can break, including cases where the horn doesn’t work at all and situations where the opposite occurs.

In this dreaded “always on” condition, an unsuspecting driver can suddenly end up with a horn that will not stop honking, no matter what they do.

How Do Car Horns Work?

Car horns rely on some pretty basic technology, and the fundamentals of most car horn systems have remained relatively unchanged for decades. The basic idea is that some type of switch, usually located somewhere in the steering wheel, activates an electric horn. Some vehicles have a single horn, and others use two horns that each operate in a different frequency range.

In a typical car horn circuit, the switch or button the driver pushes is connected to a relay. This horn relay will be connected to the horn switch, battery positive, and the horn or horns. When the driver activates the horn, the relay provides power to the horn. This creates potential failure points in the horn switch, the horn relay, the actual horn components, and the wiring.

When one of these components “fails safe,” the system just doesn’t work anymore. Potential issues here include a broken horn switch that can no longer activate the relay, a broken relay that can no longer send power to the horn, and a broken horn that just doesn’t work anymore. In the latter case, it’s possible for just one horn in a two horn pair to stop working.

If that happens, you will notice that your horn doesn’t sound right anymore, since each horn in the pair produces a different note.

The problem with this type of “fail safe” is that you won’t know the system has failed until you need your horn. If that happens, and you are unable to use your horn to alert another driver or a pedestrian, the results can be disastrous. With that in mind, it may be tough to see why this would be considered a fail safe type of a system at all.

If you’ve never had a horn fail in an “always on” condition, you may have never even realized it was possible. If you have experienced this type of failure, then it’s easy to see how this is both tremendously annoying and potentially dangerous.

The issue is that car horns are loud. The lower limit is about 93db, which is the quietest that automakers are allowed to make their horns if they want to sell them in the European Union. The average car horn is about 100-110db, and some are even louder than that.

Since sounds louder than 85db can cause hearing loss after prolonged exposure, driving around with your car horn constantly honking is clearly a bad idea. So if it won’t stop honking, what are you supposed to do?

What Causes a Horn To Not Stop Honking?

The two main reasons a car horn won’t stop honking include a failure in the switch and a failure in the relay.

While it’s possible for failures in these components to result in a horn that doesn’t work at all, it’s also possible for either one to fail in the on position.

If you find yourself in a car or truck with a horn that won’t stop honking, the most important thing to remember is to not panic. Other drivers and pedestrians may assume that you are laying on the horn in a fit of uncontrollable rage, but there’s nothing you can do about that. What you will want to do is to pull over as soon as possible, find a safe place where you aren’t in danger from other vehicles, and locate your fuse box.

The fastest way to make a malfunctioning horn stop honking is to pull the horn fuse or the horn relay. Failing that, if you are unable to immediately locate the correct fuse or relay, pulling a main fuse or disconnecting the battery will also allow you to address the problem without damaging your hearing.

If you aren’t mechanically inclined, simply removing the horn fuse or relay will allow you to drive your vehicle to a mechanic without the horn constantly honking. The fuse box may have labels printed inside the cover or in proximity to each fuse, or you may have to simply pull each fuse, in turn, until you find the right one.

How to Fix a Car Horn That Won’t Stop Honking

Once you aren’t in danger of doing permanent damage to your hearing, fixing a car horn that won’t stop honking is a simple matter of figuring out which component failed. Since different cars are wired differently, you may have to look up a diagnostic procedure specific to your vehicle. However, it’s typically a matter of determining whether the horn switch is broken or if the relay is shorted internally.

This type of diagnostic can be accomplished without any tools at all, if you’re lucky, but you will probably need some basic tools. The most important tool in your arsenal will be a multimeter. Although you can also use a test light to check for power, you’ll need an ohmmeter to check for continuity if you end up having to test the operation of your horn switch.

In some situations, you may get lucky and have a horn relay that is identical to a relay used in a different circuit. If that case, you may be able to simply swap the presumed-good relay with the horn relay, and check if the horn stops honking. If the horn works with the replacement relay, then you should be able to just buy a new relay and fix the problem.

If you aren’t lucky enough to have an identical relay for testing purposes, you will have to test the horn switch and the relay. If you find that the relay is shorted internally, then replacing it will fix the problem.

If the relay doesn’t show an internal short, then you will have to remove the relay and identify which two wires are connected to the horn switch. You can then use a multimeter to check for continuity between these wires. If the switch is in working order, pushing the horn button or pad inside your vehicle should cause a change in the reading on the multimeter.

Keep in mind that some vehicles integrate the horn switch with the airbag module. If your vehicle is set up like that, you will need to look up the correct procedures or take your car to a qualified mechanic. Accidentally setting off your airbag can be a costly, or even dangerous, mistake.

I Have No Horn, and I Must Honk

The procedure for diagnosing and fixing a horn that doesn’t honk at all is similar to fixing a horn that won’t stop honking, but there are a few additional wrinkles. The first thing to check is whether or not the horn relay is getting power. If it isn’t, then you’ll have to look at the wiring between the relay and the battery.

If the relay is getting power, you’ll also want to check whether or not pushing your horn button or pad passes power to relay terminal that is wired to your horns. If it doesn’t, there is a problem with the relay or the switch, which can be checked in the same ways as described above.

If you find that pushing your horn button or pad does result in power at the output terminal of your horn relay, there is probably an issue with the actual horn assembly or wiring. You’ll need to check for power and ground at the horns. If you find power and ground, you probably just need a new horn or horns. If there is no power or ground, then it’s a wiring issue.

The Trouble With Horns, Airbags and Car Alarms

While there are a lot of horn problems that you can fix at home without too much trouble, it's important to remember that car horns are often tied into car alarm systems, and replacing or testing a faulty horn switch may also involve dealing with an airbag module.

Since aftermarket car alarm systems are so diverse, there is no real easy fix for a car alarm that won't stop going off, or won't work at all, due to a car alarm problem. This type of problem is sometimes caused by a weak battery, or a battery that has gone dead or been disconnected, and can sometimes be fixed by pushing some combination of buttons on the alarm remote or by using the remote while the key is in the ignition. The procedure is different from one manufacturer to the next, and similar problems can also be caused by moisture and simple hardware malfunctions.

When dealing with a malfunctioning horn in a vehicle that came equipped with airbags, it's especially important to look up the correct procedure for dealing with or disarming the airbags before you do any work with the horn switch, steering wheel, or steering column. If you don't, the airbag may accidentally deploy, which may result in injury, but will definitely require you to purchase an expensive replacement airbag module.

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