I was driving through Dublin city recently in a friend’s car, Dublin streets are narrow, I found myself caught behind a cyclist with headphones on, he had no idea I was there, and I had no way to alert him – DAMN HORN DIDN’T WORK!! – You don’t miss it until it doesn’t work.
Car won’t honk? The most likely reason the car horn won’t honk is a blown fuse, but other likely causes include:
- Faulty wiring
- Faulty horn
- Faulty clock spring
- Faulty horn switch
I’m a mechanic and a broken car horn is very common, can’t imagine driving in a city without a car horn. In this post, we’ll look at each of the top five likely causes and what you can do to fix them right now.
Blown Fuse Will Stop Horn Honking
The simplest fault is sometimes the answer. Changing a fuse is easy, sometimes finding the location of the fuse box and the fuse number can be the challenging part.
Car horns like all electrical components in your car have a fuse. The element in the fuse is designed to burn out (blow) if the electrical circuit is faulty. The blown fuse stops the flow of voltage through the circuit and therefore prevents circuit wiring or component damage.
So although a blown fuse is a pain in the jacksie, it is the car’s way of letting you know there’s a problem. In theory, excessive voltage draw is the reason all fuses blow, but it’s not the root cause.
Go ahead and check your fuse, remove it and inspect it. Your car will likely have more than one fuse box so consult your driver’s manual for the correct location and fuse size. If you have a simple test light, check for power in the circuit.
In my experience the most common reasons for a blown car horn fuse, are:
- Wrong fuse size
- Faulty car horn
- Wiring fault
Car Horn Fuse
The wrong fuse size will cause problems. Fuses are graded by amps. For example, a car horn might typically have a 15 amp fuse. That simply means the circuit (wiring and component) is designed to take a max of 15 amps of power. If the circuit draws anything more than 15 amps, the fuse blows.
Using say a 25 amp fuse in that 15 amp circuit is dangerous, if a fault develops in the circuit, the fuse won’t blow as the circuit intended.
The opposite is true too, using a 15 amp in a 25 amp circuit while not dangerous, it will cause the fuse to blow. Often not straight away, which can lead you to think there’s a problem.
Tips for replacing fuses –
- Use the fuse tool attached to your fuse panel to remove and install the fuse.
- Check your fuse size in the drivers manual, don’t just assume the blown fuse size is the correct size.
A horn relay in the circuit is common and they do fail. Check your driver’s manual for a horn relay listing on the fuses and relays page. Often you’ll find many identical relays together in the fuse board. Swapping the horn relay for a known-good one is a fast hack for checking the relay function.
Alternatively, go ahead and test the relay as per the infographic below.
Faulty Car Horn
A faulty car horn can cause an excessive draw, more than the fuse is rated and of course the fuse does its job and blows. The only fix here is to replace the car horn unit.
Wiring fault is common too, if the voltage carrying wire (called the hot wire) rubs the chassis, it will wear away the insulation and ground on the chassis (known as shorting). This in turn will cause excessive voltage draw and bang goes the fuse.
This type of problem will require some detective work. Obvious places to look – anywhere the car horn wiring loom turns sharply along with the chassis.
Faulty Wiring Causes The Horn To Stop Working
Wiring issues can cause even pro mechanics to lose their S**t! I’ve always liked solving wiring problems, but modern cars can be challenging without proper test equipment like code readers and power probes.
At its most basic, an old classic car horn wiring circuit consists of:
- Power supply
- Horn switch
Not forgetting the wiring to connect it, collectively it’s known as a circuit. Most electrical problems revolve around one simple concept – there’s a break in the circle. Find the break and you find the problem.
Modern Car Horn System
Modern cars are a little more complicated. The same concept of a broken circuit applies, but modules (computers) have been added, which means there are several separate circuits employed to honk the horn. Modern car horn circuits typically consist of:
- Power supply
- Clock spring
- Horn Switch
- Steering wheel control module
- Central electronic control module
The horn switch when pressed will send a signal to the steering wheel control module (SWM) through the clock spring. The SWM will send a signal to the central electronic module (CEM). As the CEM is programmed, it sends a ground to the horn relay which closes the contacts and powers the horns.
I wrote a whole post here for How to read wiring diagrams.
These types of circuits are best diagnosed using a scan tool, but you can still troubleshoot using a humble test light.
Wiring issues are always a likely cause of broken circuits, they suffer from one of two problems:
- No connection
- Bad connection
1 No Connection
Simple enough, right! The wiring is broken or disconnected and so the circuit is open, meaning it’s no longer a circle.
Check the car horn first, make sure the two connections (one power and one ground) are fitted securely.
2 Bad Connections
The connections could simply be loose or could be corroded at the horn itself. Either way, the bad connection is enough to leave the circuit open or offers high resistance to the flow of voltage.
The next test is a power test at the horn itself, a simple test light works great but a voltmeter is good too.
Faulty Horn Refuses To Honk
The car horn is a very simple piece of kit, voltage causes the horn to vibrate. Common horn failure is caused by water inside the horn, which causes corrosion and eventually leads to failure.
It’s common for a car to have twin horns, for both to fail at once is not likely. However, I often troubleshoot car horns and find both are faulty, but they didn’t fail at the same time. The owner just didn’t notice the first horn failure.
Use Your Ears First
Often the horn will make some sound, it may be slight and you may have to put your ear to the front of the car while a helper honks it. If you can hear a click sound or any sound at all it means your wiring, modules, and switch are good, the horns are at fault and need to be replaced.
Using a power probe, apply power and ground to the two horn terminals, doesn’t matter which terminal is positive and which is ground.
If the horns fail to blow, replace them, they’re faulty.
Faulty Clock Spring Causes Horn Fault
Most car horn controls are in the center of the steering wheel. This creates an issue for wiring as the steering wheel obviously must turn left and right.
The solution is a clock spring, it’s a coil of wire that winds in and out as you turn the steering wheel, not unlike a roll-up electric cord.
The clock spring has an important job, it carries various signals from steering wheel control buttons, it’s also tasked with carrying the signal to fire the steering wheel airbag.
The constant flexing and winding of the steering wheel cause the clockspring ribbon to eventually wear out and break.
Symptoms of a broken clock spring:
- Horn doesn’t work
- Airbag light on
- Radio steering wheel buttons don’t work
- Cruse control steering wheel buttons don’t work
- Phone steering wheel buttons don’t work
- Rubbing noise when turning the steering wheel
A fault code reader is a useful tool when diagnosing a failed clock spring, a code such as B1915 will likely be logged in the on-board computer.
Replacing the clock spring requires removing the airbag and the steering wheel. Special tools may be required and a steering angle sensor may need to be calibrated after installation.
Faulty Horn Switch Causes No Honk
Classic car horn switches did give lots of problems but modern car horn switches are more durable. They are usually part of the driver’s airbag module and aren’t serviceable.
Diagnosing a faulty horn switch will require the use of a suitable scan tool, replacing the switch will require replacing the driver’s airbag module.
Does a car horn have a fuse? A car horn will have a fuse. Check your driver’s manual for the fuse box, fuse location, and the correct amp fuse rating.