Jeep Cherokee (XJ): Description and operation

Horn system

DESCRIPTION

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
  •  Horns
  •  Horn relay
  •  Horn switch
  •  Remote Keyless Entry (RKE) receiver (only with the RKE system)

Refer to Clockspring in the Description and Operation section of Group 8M - Passive Restraint Systems for more information on this component. Refer to Remote Keyless Entry System in the Description and Operation section of Group 8P - Power Lock Systems for more information on this component.

Refer to Horn/Cigar Lighter in the Contents of Group 8W - Wiring Diagrams for complete circuit diagrams. Following are general descriptions of the remaining major components in the horn system.

OPERATION

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 in the vehicle glove box for more information on the features, use and operation of the horn system.

REMOTE KEYLESS ENTRY RECEIVER

The Remote Keyless Entry (RKE) receiver can also operate the horn system. An RKE receiver is used on this vehicle when it is equipped with the optional RKE system. The RKE receiver controls and integrates the additional electronic functions and features included on models with this option. A customer programmable feature of the RKE system enables the RKE receiver to momentarily energize the horn relay through a hard wired circuit as an audible verification that the receiver has received a valid lock request from the RKE transmitter.

Refer to Remote Keyless Entry System in the Description and Operation section of Group 8P - Power Lock Systems for more information on this feature.

Horn

DESCRIPTION

The dual electromagnetic diaphragm-type horns are standard equipment on this model. The low-note horn is secured with a bracket to the left radiator closure panel brace, behind the front bumper. The high-note horn is secured with a bracket to the right radiator closure panel brace, behind the front bumper. Both horns are grounded through their mounting brackets and receives battery feed through its wire harness connector and circuit from the closed contacts of the horn relay.

The horns cannot be repaired or adjusted and, if faulty or damaged, they must be individually replaced.

OPERATION

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

DESCRIPTION

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 on the right cowl side inner panel below 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 junction block until further diagnosis is completed.

Refer to Junction Block in the Contents of Group 8W - Wiring Diagrams for horn relay identification and location.

The horn relay is a International Standards Organization (ISO) relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions.

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

OPERATION

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

DESCRIPTION

A center-blow, normally open, resistive membranetype 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 (Fig. 1). 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.

Fig. 1 Driver Side Airbag Module Trim Cover and Horn Switch
Fig. 1 Driver Side Airbag Module Trim Cover and Horn Switch

1 - RETAINER SLOTS
2 - TRIM COVER
3 - LOCKING BLOCKS
4 - RETAINER SLOTS
5 - HORN SWITCH

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.

OPERATION

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.

    Next pageDiagnosis and testing

    Horn relay The horn relay (Fig. 2) is located in the junction block on the right cowl side inner panel below the instrument panel in the passenger compartment. If a problem is encountered with a co ...

    Other materials:

    Advanced Front Air Bag Operation. Occupant Classification System (OCS) - Front Passenger Seat. Occupant Classification Module (OCM) and Sensor
    Advanced Front Air Bag Operation Advanced Front Air Bags are designed to provide additional protection by supplementing the seat belts. Advanced Front Air Bags are not expected to reduce the risk of injury in rear, side, or rollover collisions. The Advanced Front Air Bags will not deploy in all ...