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A car horn is not designed to voice your displeasure with another motorist as some people may think. Instead, it is meant to warn other drivers and any pedestrians in the vicinity to your presence in order to avoid unfortunate contact with them. A brief “toot” can, for instance, gain the attention of a pedestrian about to step off a curb into traffic without looking, or get the attention of a distracted parent trying to manage a child, instead of paying close attention to what is unfolding in the road ahead.
The car horn hasn’t changed much in the last 50 years. The system is made up of a switch or button, relay and the speaker device that outputs the sound. The components and wiring are protected by a separate fuse labeled in the main panel. The relative simplicity of the system makes it easy to diagnose maladies.
The main job of a fuse is to protect the electrical circuits in your car from a shorting or overloading. A fuse protects the wire or wires they are connected to from overheating and catching fire. Fuses are rated by their amperage and are designed to blow or open when the current being drawn through it exceeds its design rating. If a device draws enough current to blow a fuse, odds are you've got a problem that will make it blow again, sooner or later. Rarely, a fuse will fail for no apparent reason.
Horn is defunct
Most vehicles actually have two horns, wired to sound at the same time. Typically mounted to the radiator core support or somewhere behind the vehicle's front grille, each horn delivers is a different pitch, sounding a chord instead of a single note. Some luxury cars employ three horns for a more complex, melodious sound. Because they are mounted in the engine bay, horns are susceptible to the elements. They often get wet and dirty causing the electrical connections to rust -- breaking the electrical connection -- and the horns internal components to corrode.
Bad horn relay
Technically speaking, the horn relay switches a large current to the horns at a signal from the low-current horn button in the steering wheel. When the horn button is pushed it the current to flow to the relay. When the relay is energized, it closes the circuit and allows the full power to be directed to the horns.
Typically, the horn relay is a simple, inexpensive single-pole single throw (SPST) relay, packaged in a small metal or plastic box with five connectors. But it can be integrated into a larger box that also control the headlights, turn signals or other features.
Malfunctioning horn button
The horn button (or buttons) is where you press the palm of your hand to activate the horn. It’s typically mounted in the steering wheel, atop of the airbag shroud.
Bad clock spring
A clock spring is a special rotary electrical connector that allows a vehicle's steering wheel to turn while still making an electrical connection between the steering wheel airbag and/or the vehicle's horn and other devices in the vehicle's electrical systems. Your car’s airbag must be removed to access the slip rings or clock spring that carry electricity up the rotating steering column from the relay to the horn button.
If all of the above passes inspection, the wiring bad and the mechanic will identify the open circuit.
A top-rated mobile mechanic will come to your home or office to determine the cause of the inoperable horn, and will then provide a detailed inspection report that includes the scope and cost of the necessary repairs.
The U.S. Department of Transportation mandates that each vehicle be equipped with an audible warning device (i.e., a horn) and that it operates as per the intended design. Correct operation is often verified during a state inspection. A horn that is muffled or inoperative will need to be repaired before a passing grade is given. As such, it is advisable to book a mechanic to perform a thorough inspection of the inoperable horn as soon as possible.