Horn: Description and Operation
HORN SYSTEMA 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 allows the vehicle operator to provide an audible warning of the presence or approach of the vehicle to pedestrians and the drivers of other vehicles in near proximity. 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 can also be activated by the Body Control Module (BCM). The BCM is programmed to activate the horns in order to provide the following features:
- Remote Keyless Entry (RKE) system lock request audible verification (except export)
- RKE system panic mode audible alert
- Vehicle Theft Security System (VTSS) audible alarm.
This vehicle also offers several customer programmable features, which allows the selection of several optional electronic features to suit individual preferences. Refer to Overhead Console for more information on the customer programmable feature options. Customer programmable feature options affecting the horn system include:
- Sound Horn on Lock - Allows the option of having the horn sound a short chirp as an audible verification that the RKE system received a valid Lock request from the RKE transmitter, or having no audible verification.
The horn system includes the following components:
- Clockspring
- Horns
- Horn relay
- Horn switch
Certain functions and features of the horn system rely upon resources shared with other electronic modules in the vehicle over the Programmable Communications Interface (PCI) data bus network. The PCI data bus network allows the sharing of sensor information. This helps to reduce wire harness complexity, internal controller hardware, and component sensor current loads. At the same time, this system provides increased reliability, enhanced diagnostics, and allows the addition of many new feature capabilities. For diagnosis of these electronic modules or of the PCI data bus network, the use of a DRB scan tool and the proper Diagnostic Procedures are recommended.
The other electronic modules that may affect horn system operation are as follows:
- Body Control Module (BCM) (Refer to ELECTRICAL/ELECTRONIC CONTROL MODULES/BODY CONTROL/CENTRAL TIMER MODUL - DESCRIPTION) for more information.
- Electronic Vehicle Information Center (EVIC) (Refer to ELECTRICAL/OVERHEAD CONSOLE/ELECTRONIC VEHICLE INFO CENTER - DESCRIPTION) for more information.
(Refer to ELECTRICAL/RESTRAINTS/CLOCKSPRING - DESCRIPTION) for more information on this component. Refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds. Following are general descriptions of the remaining major components in the horn system.
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.
The BCM can also activate the horn system by energizing the horn relay through a single hard wired output circuit. The BCM energizes and de-energizes the horn relay in response to internal programming as well as message inputs received over the Programmable Communications Interface (PCI) data bus network. The BCM can energize the horn relay for a single chirp (RKE lock request), or for extended operation (RKE panic mode and VTSS alarm mode).
Refer to the owner's manual in the vehicle glove box for more information on the features, use and operation of the horn system.
HORN
The dual electromagnetic diaphragm-type horns are standard equipment on this model. Both horns are secured to a mounting bracket. The mounting bracket is secured with a screw to the back side of the right extension of the radiator closure assembly, just ahead of the right front wheel house and below the front wheel house extension. The two horns are connected in parallel. Each horn is grounded through its wire harness connector and circuit to an eyelet secured to the right inner fender shield near the battery, 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 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 Power Distribution Center (PDC) in the engine compartment. If a problem is encountered with a continuously sounding horn, it can usually be quickly resolved by removing the horn relay from the PDC until further diagnosis is completed. See the fuse and relay layout label affixed to the inside surface of the PDC cover 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.
HORN SWITCH
A center-blow, normally open, resistive membrane-type horn switch is secured in a plastic tray that is inserted in a pocket sewn on the front of the driver side airbag retainer strap. The horn switch is concealed behind 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 and plastic tray are serviced as a unit. If the horn switch is damaged or faulty, or if the driver side airbag is deployed, the horn switch and tray 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.