Horn: Description and Operation

HORN SYSTEM
A dual-note electric horn system is standard factory-installed equipment on this model. The standard equipment horn system features one low-note horn unit and one high-note horn unit. The horn system uses a non-switched source of battery current so that the system will remain functional, regardless of the ignition switch position. The horn system includes the following components:
- Clockspring
- High-line Central Timer Module (CTM)
- Horns
- Horn relay
- Horn switch

(Refer to ELECTRICAL/RESTRAINTS/CLOCKSPRING - DESCRIPTION) for more information on this component. (Refer to ELECTRICAL/ELECTRONIC CONTROL MODULES/BODY CONTROL/ CENTRAL TIMER MODUL - DESCRIPTION) for more information on this component.

The horn system is activated by a horn switch concealed beneath the driver side airbag module trim cover in the center of the steering wheel. Depressing the center of the driver side airbag module trim cover closes the horn switch. Closing the horn switch activates the horn relay. The activated horn relay then switches the battery current needed to energize the horns.

Refer to the owner's manual for more information on the features, use and operation of the horn system.

The high-line Central Timer Module (CTM) can also operate the horn system. A high-line CTM is used on high-line versions of this vehicle. The CTM combines the functions of a chime/buzzer module, an intermittent wipe module, an illuminated entry module, a remote keyless entry module, and a vehicle theft security system module in a single unit.

The high-line CTM also controls and integrates many of the additional electronic functions and features included on models with this option. The horn relay is one of the hard wired outputs of the CTM. The high-line CTM is programmed to energize or deenergize the horn relay in response to certain inputs from the Remote Keyless Entry (RKE) system and/or the Vehicle Theft Security System (VTSS).

(Refer to ELECTRICAL/ELECTRONIC CONTROL MODULES/BODY CONTROL/CENTRAL TIMER MODULE - DESCRIPTION) for more information on the high-line CTM. (Refer to ELECTRICAL/POWER LOCKS - GENERAL INFORMATION) for more information on the RKE system. Refer to (Refer to ELECTRICAL/VEHICLE THEFT SECURITY - GENERAL INFORMATION) for more information on the VTSS.

HORN
The dual electromagnetic diaphragm-type horns are standard equipment on this model. Both horns are mounted on a single bracket that is secured to the front of the left vertical member of the radiator support, just behind the radiator grille and forward of the radiator. The high-note horn is connected in parallel with the low-note horn. The horns are connected to the vehicle electrical system through the headlamp and dash wire harness. Each horn is grounded through its wire harness connector and a ground circuit to an eyelet terminal secured by a ground screw located on the right front inner fender behind the right headlamp, and receives battery current through the closed contacts of the horn relay

Both horns and the mounting bracket are serviced as a single unit. The horns cannot be repaired or adjusted and, if faulty or damaged, the entire horn and bracket unit must be replaced.

Within the two halves of the molded plastic horn housing are a flexible diaphragm, a plunger, an electromagnetic coil and a set of contact points. The diaphragm is secured in suspension around its perimeter by the mating surfaces of the horn housing. The plunger is secured to the center of the diaphragm and extends into the center of the electromagnetic coil. The contact points control the current flow through the electromagnet.

When the horn is energized, electrical current flows through the closed contact points to the electromagnet. The resulting electromagnetic field draws the plunger and diaphragm toward it 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 the vibration and movement of air that creates the sound that is directed through the horn outlet.

HORN RELAY
The horn relay is a electromechanical device that switches battery current to the horn when the horn switch grounds the relay coil. The horn relay is located in the Junction Block (JB), on the left end of the instrument panel in the passenger compartment. If a problem is encountered with a continuously sounding horn, it can usually be quickly resolved by removing the horn relay from the JB until further diagnosis is completed. See the fuse and relay layout label affixed to the inside surface of the fuse access panel for horn relay identification and location.

The horn relay is a International Standards Organization (ISO) micro-relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The ISO micro-relay terminal functions are the same as a conventional ISO relay. However, the ISO micro-relay terminal pattern (or footprint) is different, the current capacity is lower, and the physical dimensions are smaller than those of the conventional ISO relay.

The horn relay cannot be repaired or adjusted and, if faulty or damaged, it must be replaced.

The ISO relay consists of an electromagnetic coil, a resistor or diode, and three (two fixed and one movable) electrical contacts. The movable (common feed) relay contact is held against one of the fixed contacts (normally closed) by spring pressure. When the electromagnetic coil is energized, it draws the movable contact away from the normally closed fixed contact, and holds it against the other (normally open) fixed contact.

When the electromagnetic coil is de-energized, spring pressure returns the movable contact to the normally closed position. The resistor or diode is connected in parallel with the electromagnetic coil in the relay, and helps to dissipate voltage spikes that are produced when the coil is de-energized.

Fig.3 Driver Side Airbag Module Trim Cover And Horn Switch:

HORN SWITCH
A center-blow, normally open, resistive membrane-type horn switch is secured with heat stakes to the back side of the driver side airbag module trim cover in the center of the steering wheel. The switch consists of two plastic membranes, one that is flat and one that is slightly convex. These two membranes are secured to each other around the perimeter. Inside the switch, the centers of the facing surfaces of these membranes each has a grid made with an electrically conductive material applied to it. One of the grids is connected to a circuit that provides it with continuity to ground at all times. The grid of the other membrane is connected to the horn relay control circuit.

The steering wheel and steering column must be properly grounded in order for the horn switch to function properly The horn switch is only serviced as a part of the driver side airbag trim cover. If the horn switch is damaged or faulty, or if the driver side airbag is deployed, the driver side airbag trim cover and horn switch must be replaced as a unit (Refer to ELECTRICAL/RESTRAINTS/DRIVER AIRBAG - REMOVAL).

When the center area of the driver side airbag trim cover is depressed, the electrically conductive grids on the facing surfaces of the horn switch membranes contact each other, closing the switch circuit. The completed horn switch circuit provides a ground for the control coil side of the horn relay, which activates the relay. When the horn switch is released, the resistive tension of the convex membrane separates the two electrically conductive grids and opens the switch circuit.