Jeep Cherokee (XJ): Description and operation
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: 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. 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. 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. 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.
1 - RETAINER SLOTS 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.Horn system
Horn
Horn relay
Horn switch
Fig. 1 Driver Side Airbag Module Trim Cover and Horn Switch
2 - TRIM COVER
3 - LOCKING BLOCKS
4 - RETAINER SLOTS
5 - HORN SWITCH
Other materials:
Driver memory seat
This feature allows the driver to store up to two different
memory profiles, for easy recall through a memory
switch. Each memory profile contains desired position
settings for the driver seat and side mirrors and a set of
desired radio station presets.
The memory switch is located on the dri ...
