Horn: Description and Operation

HORN SYSTEM
A dual-note electric horn system is standard factory-installed equipment on this model . The dual-note horn system features dual electromagnetic horn units, which provide an audibly louder and fuller sounding horn tone than a single-note system. The horn system includes the following major components, which are described in further detail:
- Horn - The two horn units are locate behind the front bumper, one on each side just outboard of the radiator closure panel.
- Horn Relay - The horn relay is located in the Junction Block (JB) on the right inner cowl side panel in the passenger compartment of the vehicle.
- Horn Switch - The horn switch is located in the center of the steering wheel, behind the driver airbag trim cover.

Hard wired circuitry connects the horn system components to each other through the electrical system of the vehicle. These hard wired circuits are integral to several wire harnesses, which are routed throughout the vehicle and retained by many different methods. These circuits may be connected to each other, to the vehicle electrical system and to the horn system components through the use of a combination of soldered splices, splice block connectors and many different types of wire harness terminal connectors and insulators.

The horn system is designed to provide an audible alert to nearby pedestrian or vehicular traffic of the presence or approach of the vehicle. The vehicle operator can activate the horn system manually by depressing the horn switch concealed beneath the driver airbag trim cover in the center of the steering wheel. During manual horn system operation, the horns will continue to sound for as long as the vehicle operator keeps the horn switch depressed.

In vehicles equipped with the optional Remote Keyless Entry (RKE) system, the horn system can also be activated by the vehicle operator remotely using the Panic feature of the RKE system. Depressing the Panic button on the RKE transmitter activates the Panic mode. When the Panic mode is activated the horns will pulse ON and OFF for a preprogrammed interval. The RKE system also has a customer programmable horn chirp feature that, if enabled, will momentarily activate the horn system to deliver a single short chirp of the horns as an audible confirmation that an RKE Lock request has been received and fulfilled. Refer to Power Locks for additional information on the features of the RKE system.

The horn system operates on battery current received through two fused B(+) circuits. The horn control circuit is protected by a fuse in the Junction Block (JB), while the horn output circuit is protected by a fuse in the Power Distribution Center (PDC). These horn system circuits are designed so that the system will remain operational, regardless of the ignition switch position. See the owner's manual in the vehicle glove box for more information on the features, use and operation of the horn system.

Fig.1 Horn:

HORN
Dual electromagnetic diaphragm-type horns are standard equipment on this model. Both horns include an integral, stamped steel, stepped strap mounting bracket. Each horn and bracket unit is secured with a screw to a radiator closure panel brace behind the front bumper. The low-note horn is secured to the left brace, and the high-note horn is secured to the right brace. The two horns are connected in parallel electrically.

The low-note and high-note horns are very similar in appearance, but are identified by a "Lo" or "Hi" tone designation that is permanently molded or stamped into the molded plastic, conch shell-like horn outlet. Each horn unit has a threaded mounting stud protruding from the center of the metal housing, which is used to secure it with a nut to the mounting bracket. A washer between the nut and the mounting bracket is stamped with the voltage and frequency ratings of the horn unit. A single connector receptacle riveted to the external surface of the horn housing connects the horn to the vehicle electrical system.

The basic construction of all electromagnetic diaphragm-type horns is very similar. A typical horn consists of the following major components:
- Coil - A tightly wound coil of wire that produces an electromagnetic field when electrical current passes through it.
- Contacts - A normally closed set of contact points, one fixed contact point and one movable contact point, that control the flow of electrical current through the coil.
- Diaphragm - The flexible metal membrane that is vibrated rapidly to move the air within the horn to produce sound waves.
- Housing - This is the fixed chassis or support structure to or within which all of the other horn components are secured.
- Outlet - This is the molded plastic air passage that collects, magnifies and directs the sound waves produced within the horn.
- Plunger - The metal piston-like member secured to the center of the diaphragm and suspended within the windings of the coil.

The factory-installed horns cannot be adjusted or repaired. An adjustment screw located on the horn housing is used to tune the horn unit during manufacturing, but should not be tampered with by service personnel. Attempts to adjust the horn may result in premature horn failure. If a horn or its mounting bracket is damaged or faulty, the entire horn unit must be replaced.

Electromagnetic horns convert electrical energy into a mechanical movement of the air within the horn in order to produce an audible sound. When the horn is energized, electrical current flows through the normally closed contact points to the electromagnetic coil. The resulting electromagnetic field draws the metal plunger and flexible diaphragm toward the coil until that movement mechanically opens the contact points. When the contact points open, the electromagnetic field collapses allowing the plunger and diaphragm to return to their relaxed positions and closing the contact points again. This cycle continues repeating at a very rapid rate producing a vibrating movement of the metal diaphragm. The vibrating diaphragm moves the air within the horn creating sound waves. The sound waves are collected within the horn outlet, which magnifies and directs the sound waves in a manner similar to a megaphone.

Each horn is connected to the vehicle electrical system through a separate take out and connector in the headlamp and dash wire harness. The horn is grounded at all times through its mounting. The horn receives battery current through a fused B(+) fuse in the Power Distribution Center (PDC) on the horn relay output circuit only when the horn relay control coil is energized.

Fig.3 Junction Block Location:

HORN RELAY
The horn relay is located in the Junction Block (JB) on the right cowl side inner panel, below the instrument panel in the passenger compartment (Fig.3). The horn relay is a conventional International Standards Organization (ISO) mini relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The relay is contained within a small, rectangular, molded plastic housing. The relay is connected to all of the required inputs and outputs through the JB connector receptacles by five male spade-type terminals that extend from the bottom of the relay base. The ISO designation for each terminal is molded into the base adjacent to the terminal. The ISO terminal designations are as follows:
- 30 (Common Feed) - This terminal is connected to the movable contact point of the relay.
- 85 (Coil Ground) - This terminal is connected to the ground feed side of the relay control coil.
- 86 (Coil Battery) - This terminal is connected to the battery feed side of the relay control coil.
- 87 (Normally Open) - This terminal is connected to the normally open fixed contact point of the relay.
- 87A (Normally Closed) - This terminal is connected to the normally closed fixed contact point of the relay.
The horn relay cannot be adjusted or repaired. If the relay is damaged or faulty, it must be replaced.

The horn relay-is an electromechanical switch that uses a low current input from the horn switch to control a high current output to the horns. The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. A resistor or diode is connected in parallel with the relay coil in the relay, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The horn relay terminals are connected to the vehicle electrical system through a connector receptacle in the Junction Block (JB). The inputs and outputs of the horn relay include:
- The common feed terminal (30) receives a battery current input from a fuse in the JB through a fused B(+) circuit at all times.
- The coil ground terminal (85) receives a ground feed input from the horn switch through the horn relay control circuit whenever the contacts of the horn switch are closed. On models with the optional Remote Keyless Entry (RKE) system, the horn relay control circuit can also be pulled to ground by the RKE module.
- The coil battery terminal (86) receives a battery current input from a fuse in the Power Distribution Center (PDC) through a fused E(+) circuit at all times.
- The normally open terminal (87) provides a battery current output to the horns through the horn relay output circuit only when the horn relay control coil is energized.
- The normally closed terminal (87A) is not connected to any circuit in this application, but battery current should be present at this terminal whenever the horn relay control coil is de-energized.

HORN SWITCH

Fig.6 Horn Switch:

A single pole, single throw, center-blow, normally open, resistive membrane-type horn switch is secured with heat stakes to the back side of the driver airbag trim cover. When installed, the horn switch is concealed behind the trim cover near the center of the steering wheel. An International Control and Display Symbol for horn is molded into the face of the trim cover to identify the horn switch location to the vehicle operator. The driver airbag trim cover has a regular grid of small nubs molded into the inner surface of the cover directly over the horn switch. When the driver airbag trim cover is installed on the airbag housing, the horn switch is sandwiched between the trim cover and the airbag.

Fig.7 Driver Airbag Trim Cover Removal/Install:

The horn switch consists of two thin, flexible, clear plastic membranes. The center fields of the facing surfaces of these two membranes each has a switch contact laminated to it. The switch contacts are constructed of a thin, electrically conductive copper film. A grid of small, resilient, non-conductive dots applied at regular intervals within the field of one of the switch contacts and a thin bead of the same material is applied around the perimeter of the contact. This non-conductive material suspends and insulates one contact from the other contact, effectively holding the switch open after the edges of the two membranes have been bonded together. Each of two small tabs that extend from the upper edge of the horn switch membranes have a short pigtail wire riveted to it. These pigtail wires connect the two horn switch contact membranes to the vehicle electrical system. The black pigtail wire on the left tab has an eyelet terminal connector on its loose end, while the loose end of the red pigtail wire on the right side has a male spade terminal connector.

The horn switch is only serviced as a part of the driver airbag trim cover. Refer to Driver Airbag for the proper driver airbag trim cover service procedures. The horn switch cannot be adjusted or repaired. If the horn switch is damaged or faulty, the driver airbag trim cover and the horn switch must be replaced as a unit.

The horn switch allows the vehicle operator to manually control the operation of the horn system. When the center area of the driver airbag trim cover is depressed, the nubs on the inside of the cover contact and compress the horn switch membranes. Compression of the horn switch membranes forces the two electrically conductive contact surfaces within the horn switch against each other and closes the horn switch circuit. When the driver airbag trim cover is released, the combined resistive tension created by the non-conductive resilient dots and bead on the one switch contact restore the separation between the two electrically conductive contact surfaces and open the switch circuit.

The only input to the horn switch is a ground feed that is connected to one of the switch contacts through the black pigtail wire. The eyelet terminal connector of the black pigtail wire is secured under a hex nut and washer to the upper left stud of the airbag inflator on the back of the airbag housing and is grounded through this connection when the airbag housing is installed on the steering wheel. The only output from the closed horn switch contacts is the ground path it provides to the horn relay through the red pigtail wire of the horn switch on the horn relay control circuit. The male spade terminal of the red pigtail wire is connected to a mating connector on a take out of the steering wheel wire harness.