Horn: Description and Operation
HORN SYSTEMAn electric horn system is standard factory-installed equipment on this model. Two horn systems are offered on this model. The standard equipment horn system features a single low-note electromagnetic horn unit, while the optional dual horn system features one low-note horn unit and one high-note horn unit. Both horn systems use 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:
- Central Timer Module (CTM) (with Vehicle Theft Security System only)
- Horn(s)
- Horn relay
- Horn switch
- Horn tower
- Horn contact
Following are general descriptions of the remaining major components in the horn system.
Each 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 horn(s).
Refer to the owner's manual in the vehicle glove box for more information on the features, use and operation of the horn system.
CENTRAL TIMER MODULE
The Central Timer Module (CTM) can also operate the horn system. A CTM is used on this vehicle when it is equipped with the optional Vehicle Theft Security System. In addition to serving as the security system module, the CTM combines the functions of a chime/buzzer module, an intermittent wipe module, an illuminated entry module, and a Remote Keyless Entry module in a single unit.
The 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 CTM is programmed to energize or de-energize the horn relay in response to certain inputs from the Vehicle Theft Security System (VTSS) and the Remote Keyless Entry (RKE) system.
Refer to Vehicle Theft Security System for more information on the VTSS. Refer to Remote Keyless Entry system for more information on the RKE system.
HORN
The standard single, low-note, electromagnetic diaphragm-type horn is secured with a bracket to the Anti-Lock Brake System (ABS) access plate located behind the outer fender extension panel under the left headlamp. The high-note horn for the optional dual-note horn system is connected in parallel with and secured with a bracket just inboard of the low- note horn. Each horn is grounded through its wire harness connector and circuit to an eyelet on the left side of the dash panel, and receives battery feed through the closed contacts of the horn relay.
The horns cannot be repaired or adjusted and, if faulty or damaged, they must be individually 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 electromagnet. 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 CONTACT
Multi-Function Switch:
A spring-loaded horn contact is integral to the multi-function switch unit, which is secured to the left side of the steering column. The only visible parts of the multi-function switch are the control stalk that extends from the left side of the steering column, and the hazard warning switch push button that protrudes from the top of the steering column. The remainder of the multi-function switch is concealed beneath the steering column shrouds.
The multi-function switch also contains circuitry for the following functions:
- Turn signals
- Hazard warning
- Headlamp beam selection
- Headlamp optical horn
- Windshield wipers
- Windshield washers.
The information contained addresses only the multi-function switch horn contact. However, the horn contact cannot be repaired. If the horn contact or any other circuit or component of the multi-function switch is faulty or damaged, the entire multi-function switch assembly must be replaced.
The spring-loaded horn contact rides against the electrically conductive disc on the lower side of the turn signal cancel cam unit. The horn contact receives the feed from the horn switch through the horn tower and turn signal cancel cam unit. A wiring circuit from the horn contact runs through the multifunction switch and its wire harness connector to one of the control coil terminals of the horn relay in the junction block.
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 relay and fuse block on the driver side 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 relay and fuse block until further diagnosis is completed.
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.
HORN SWITCH
Driver Side Airbag Module Trim Cover and 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 module trim cover. If the horn switch is damaged or faulty, or if the driver side airbag is deployed, the driver side airbag module trim cover and horn switch must be replaced as a unit.
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.
HORN TOWER
Horn Tower:
The horn tower is integral to the turn signal cancel cam, which is installed in the steering column below the shaft lock shield and the clockspring. This unit provides turn signal cancellation as well as a constant electrical contact between the horn switch on the steering wheel and the horn feed circuit in the multi-function switch.
The horn tower and turn signal cancel cam unit cannot be repaired and, if faulty or damaged it must be replaced.
The horn tower protrudes from the upper surface of the turn signal cancel cam. The horn tower passes through holes in the steering column shaft lock shield and the hub of the clockspring, which cause.' the entire turn signal cancel cam to turn with the steering wheel rotation.
An electrically conductive disc, which is coated with a special synthetic grease, is integral to the lower surface of the turn signal cancel cam. An electrical contact on one end of the horn switch feed wire is inserted into the horn tower from the top of the turn signal cancel cam, and is held against the steering wheel side of the conductive disc by a spring an( locking retainer. A spring-loaded horn contact that protrudes from the upper surface of the multi-function switch housing on the left side of the steering column rides against and remains in constant contact with the lower surface of the conductive disc.