2002 JEEP GRAND CHEROKEE Control

(6) Disconnect the 22-way instrument panel wire
harness connector from the Body Control Module
(BCM) connector receptacle. Check for continuity
between the seat heater switch sensor ground circuit
cavity of the instrument panel wire harness connec-
tor for the inoperative heated seat switch(es) and a
good ground. There should be no continuity. If OK, go
to Step 7. If not OK, repair the shorted seat heater
switch sensor ground circuit as required.
(7) Check for continuity between the seat heater
switch sensor ground circuit cavities of the instru-
ment panel wire harness connector for the in opera-
tive heated seat switch(es) and the 22-way
instrument panel wire harness connector for the
BCM. There should be continuity. If OK, go to Step 8.
If not OK, repair the open seat heater switch sensor
ground circuit as required.
(8) Check for continuity between the seat heater
switch mux circuit cavity of the instrument panel
wire harness connector for the inoperative heated
seat switch and a good ground. There should be no
continuity. If OK, go to Step 9. If not OK, repair the
shorted seat heater switch mux circuit as required.
(9) Check for continuity between the seat heater
switch mux circuit cavity of the instrument panel
wire harness connector for the inoperative heated
seat switch and the 22-way instrument panel wire
harness connector for the BCM. There should be con-
tinuity. If OK, use a DRBtscan tool and the proper
Diagnostic Procedures manual to test the BCM. If
not OK, repair the open seat heater switch mux cir-
cuit as required.
REMOVAL
WARNING: REFER TO THE RESTRAINTS SECTION
OF THIS MANUAL BEFORE ATTEMPTING ANY
STEERING WHEEL, STEERING COLUMN, OR
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the center lower bezel from the instru-
ment panel. Refer toInstrument Panel CenterLower Bezelin the Body section of this manual for
the procedure.
(3) Remove the four screws that secure the heated
seat switch to the back of the instrument panel cen-
ter lower bezel (Fig. 9).
(4) Remove the heated seat switch from the back
of the instrument panel center lower bezel.INSTALLATION
(1) Position the heated seat switch onto the back
of the instrument panel center lower bezel.
(2) Install and tighten the four screws that secure
the heated seat switch to the back of the instrument
panel center lower bezel. Tighten the screws to 1.5
N´m (13 in. lbs.).
(3) Install the center lower bezel onto the instru-
ment panel. Refer toInstrument Panel Center
Lower Bezelin the Body section of this manual for
the procedure.
(4) Reconnect the battery negative cable.
Fig. 9 Heated Seat Switch Remove/Install
1 - HEATED SEAT SWITCHES
2 - SCREWS (4)
3 - CENTER LOWER BEZEL
4 - CIGAR LIGHTER
5 - ILLUMINATION LAMPS
6 - POWER OUTLET
WJHEATED SEAT SYSTEM 8G - 17
PASSENGER HEATED SEAT SWITCH (Continued)

HORN
TABLE OF CONTENTS
page page
HORN SYSTEM
DESCRIPTION..........................1
OPERATION............................2
DIAGNOSIS AND TESTING - HORN SYSTEM . . . 2
HORN
DESCRIPTION..........................3
OPERATION............................3
DIAGNOSIS AND TESTING - HORN..........3
REMOVAL.............................3
INSTALLATION..........................4
HORN RELAY
DESCRIPTION..........................4OPERATION............................4
DIAGNOSIS AND TESTING - HORN RELAY....4
REMOVAL.............................5
INSTALLATION..........................5
HORN SWITCH
DESCRIPTION..........................6
OPERATION............................6
DIAGNOSIS AND TESTING - HORN SWITCH . . . 6
REMOVAL.............................7
INSTALLATION..........................7
HORN SYSTEM
DESCRIPTION
A dual-note electric horn system is standard facto-
ry-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:
²Remote Keyless Entry (RKE) system lock
request audible verification (except export)
²RKE system panic mode audible alert
²Vehicle Theft Security System (VTSS) audible
alarm.
This vehicle also offers several customer program-
mable features, which allows the selection of several
optional electronic features to suit individual prefer-
ences. Refer to Overhead Console for more informa-
tion on the customer programmable feature options.
Customer programmable feature options affecting the
horn system include:
²Sound 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 compo-
nents:
²Clockspring
²Horns
²Horn relay
²Horn switch
Certain functions and features of the horn system
rely upon resources shared with other electronic
modules in the vehicle over the Programmable Com-
munications Interface (PCI) data bus network. The
PCI data bus network allows the sharing of sensor
information. This helps to reduce wire harness com-
plexity, 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 capabil-
ities. 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 manual
are recommended.
The other electronic modules that may affect horn
system operation are as follows:
²Body Control Module (BCM)(Refer to 8 -
ELECTRICAL/ELECTRONIC CONTROL MOD-
ULES/BODY CONTROL/CENTRAL TIMER MODUL
- DESCRIPTION) for more information.
²Electronic Vehicle Information Center
(EVIC)(Refer to 8 - ELECTRICAL/OVERHEAD
CONSOLE/ELECTRONIC VEHICLE INFO CENTER
- DESCRIPTION) for more information.
(Refer to 8 - ELECTRICAL/RESTRAINTS/CLOCK-
SPRING - DESCRIPTION) for more information on
this component. Refer to the appropriate wiring
information. The wiring information includes wiring
diagrams, proper wire and connector repair proce-
dures, details of wire harness routing and retention,
WJHORN 8H - 1

CONDITION POSSIBLE CAUSES CORRECTION
HORN SOUNDS
CONTINUOUSLY1. Faulty horn relay. 1. Refer to Horn Relay for the proper horn relay
diagnosis and testing procedures. Replace the
horn relay or repair the shorted horn relay control
circuit, if required.
2. Faulty horn switch. 2. Refer to Horn Switch for the proper horn switch
diagnosis and testing procedures. Replace the
horn switch or repair the shorted horn switch
circuit, if required.
HORN
DESCRIPTION
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 bat-
tery, 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.
OPERATION
Within the two halves of the molded plastic horn
housing are a flexible diaphragm, a plunger, an elec-
tromagnetic coil and a set of contact points. The dia-
phragm is secured in suspension around its
perimeter by the mating surfaces of the horn hous-
ing. The plunger is secured to the center of the dia-
phragm 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 electro-
magnet. 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 con-
tact points again. This cycle continues repeating at a
very rapid rate producing the vibration and move-
ment of air that creates the sound that is directed
through the horn outlet.
DIAGNOSIS AND TESTING - HORN
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.
(1) Disconnect the wire harness connector(s) from
the horn connector receptacle(s). Measure the resis-
tance between the ground circuit cavity of the horn(s)
wire harness connector(s) and a good ground. There
should be no measurable resistance. If OK, go to Step
2. If not OK, repair the open ground circuit to ground
as required.
(2) Check for battery voltage at the horn relay out-
put circuit cavity of the horn(s) wire harness connec-
tor(s). There should be zero volts. If OK, go to Step 3.
If not OK, repair the shorted horn relay output cir-
cuit or replace the faulty horn relay as required.
(3) Depress the horn switch. There should now be
battery voltage at the horn relay output circuit cavity
of the horn(s) wire harness connector(s). If OK,
replace the faulty horns. If not OK, repair the open
horn relay output circuit to the horn relay as
required.
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Raise and support the vehicle.
(3) Remove the lower front half of the inner liner
from the right front fender wheel house. (Refer to 23
- BODY/EXTERIOR/FRONT FENDER - REMOVAL).
(4) Reach through the front of the right front
fender wheel house opening to access and disconnect
the two right headlamp and dash wire harness con-
nectors from the horn connector receptacles (Fig. 1).
Be certain to disengage the connector lock tabs
before disconnecting them from the horn connector
receptacles.
(5) Remove the screw that secures the horn
mounting bracket to the right extension of the radi-
ator closure assembly.
WJHORN 8H - 3
HORN SYSTEM (Continued)

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO ELECTRICAL, RESTRAINTS
BEFORE ATTEMPTING ANY STEERING WHEEL,
STEERING COLUMN, OR INSTRUMENT PANEL
COMPONENT DIAGNOSIS OR SERVICE. FAILURE
TO TAKE THE PROPER PRECAUTIONS COULD
RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT
AND POSSIBLE PERSONAL INJURY.
(1) Remove the horn relay from the PDC. (Refer to
8 - ELECTRICAL/HORN/HORN RELAY -
REMOVAL) for the procedures.
(2) A relay in the de-energized position should
have continuity between terminals 87A and 30, and
no continuity between terminals 87 and 30. If OK, go
to Step 3. If not OK, replace the faulty relay.
(3) Resistance between terminals 85 and 86 (elec-
tromagnet) should be 75   5 ohms. If OK, go to Step
4. If not OK, replace the faulty relay.
(4) Connect a battery to terminals 85 and 86.
There should now be continuity between terminals
30 and 87, and no continuity between terminals 87A
and 30. If OK, perform the Relay Circuit Test that
follows. If not OK, replace the faulty relay.
RELAY CIRCUIT TEST
(1) The relay common feed terminal cavity (30) is
connected to battery voltage and should be hot at all
times. If OK, go to Step 2. If not OK, repair the open
circuit to the fuse in the PDC as required.
(2) The relay normally closed terminal (87A) is
connected to terminal 30 in the de-energized position,
but is not used for this application. Go to Step 3.(3) The relay normally open terminal (87) is con-
nected to the common feed terminal (30) in the ener-
gized position. This terminal supplies battery voltage
to the horn(s). There should be continuity between
the cavity for relay terminal 87 and the horn relay
output circuit cavity of each horn wire harness con-
nector at all times. If OK, go to Step 4. If not OK,
repair the open circuit to the horn(s) as required.
(4) The coil battery terminal (86) is connected to
the electromagnet in the relay. It is connected to bat-
tery voltage and should be hot at all times. Check for
battery voltage at the cavity for relay terminal 86. If
OK, go to Step 5. If not OK, repair the open circuit to
the fuse in the PDC as required.
(5) The coil ground terminal (85) is connected to
the electromagnet in the relay. It is grounded
through the horn switch when the horn switch is
depressed. The horn relay coil ground terminal can
also be grounded by the Body Control Module (BCM)
in response to certain inputs related to the RKE sys-
tem or the Vehicle Theft Security System. Check for
continuity to ground at the cavity for relay terminal
85. There should be continuity with the horn switch
depressed, and no continuity with the horn switch
released. If not OK, (Refer to 8 - ELECTRICAL/
HORN/HORN SWITCH - DIAGNOSIS AND TEST-
ING).
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the cover from the Power Distribution
Center (PDC) (Fig. 3) .
(3) See the fuse and relay layout label affixed to
the underside of the PDC cover for horn relay iden-
tification and location.
(4) Remove the horn relay from the PDC.
INSTALLATION
(1) See the fuse and relay layout label affixed to
the underside of the PDC cover for the proper horn
relay location.
(2) Position the horn relay in the proper receptacle
in the PDC.
(3) Align the horn relay terminals with the termi-
nal cavities in the PDC receptacle.
(4) Push down firmly on the horn relay until the
terminals are fully seated in the terminal cavities in
the PDC receptacle.
(5) Install the cover onto the PDC.
(6) Reconnect the battery negative cable.
Fig. 2 Horn Relay
30 - COMMON FEED
85 - COIL GROUND
86 - COIL BATTERY
87 - NORMALLY OPEN
87A - NORMALLY CLOSED
WJHORN 8H - 5
HORN RELAY (Continued)

HORN SWITCH
DESCRIPTION
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 con-
cealed 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 mem-
branes are secured to each other around the perime-
ter. 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 pro-
vides 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.
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.
DIAGNOSIS AND TESTING - HORN SWITCH
For complete circuit diagrams, refer to the appro-
priate 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 connec-
tors, splices and grounds.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO ELECTRICAL, RESTRAINTS
BEFORE ATTEMPTING ANY STEERING WHEEL,
STEERING COLUMN, OR INSTRUMENT PANEL
COMPONENT DIAGNOSIS OR SERVICE. FAILURE
TO TAKE THE PROPER PRECAUTIONS COULD
RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT
AND POSSIBLE PERSONAL INJURY.
(1) Disconnect and isolate the battery negative
cable. Remove the steering column opening cover
from the instrument panel.
(2) Check for continuity between the metal steer-
ing column jacket and a good ground. There should
be continuity. If OK, go to Step 3. If not OK, refer to
Steering, Column for proper installation of the steer-
ing column.
(3) Remove the driver side airbag module from the
steering wheel. Disconnect the horn switch wire har-
ness connectors from the driver side airbag module.
(4) Remove the horn relay from the Power Distri-
bution Center (PDC). Check for continuity between
the steering column half of the horn switch feed wire
harness connector and a good ground. There should
be no continuity. If OK, go to Step 5. If not OK,
repair the shorted horn relay control circuit to the
horn relay in the PDC as required.
(5) Check for continuity between the steering col-
umn half of the horn switch feed wire harness con-
nector and the horn relay control circuit cavity for
the horn relay in the PDC. There should be continu-
ity. If OK, go to Step 6. If not OK, repair the open
horn relay control circuit to the horn relay in the
PDC as required.
Fig. 3 Power Distribution Center
1 - RIGHT FENDER
2 - BATTERY
3 - POWER DISTRIBUTION CENTER
4 - COVER
8H - 6 HORNWJ
HORN RELAY (Continued)

IGNITION CONTROL
TABLE OF CONTENTS
page page
IGNITION CONTROL
DESCRIPTION..........................1
OPERATION............................1
SPECIFICATIONS
ENGINE FIRING ORDER - 4.0L 6-CYLINDER
ENGINE..............................2
ENGINE FIRING ORDERÐ4.7L V-8 ENGINE . . 2
IGNITION COIL RESISTANCE - 4.0L ENGINE . 2
IGNITION COIL RESISTANCEÐ4.7L V-8
ENGINE..............................2
IGNITION TIMING......................2
SPARK PLUGS........................3
TORQUE - IGNITION SYSTEM............3
AUTO SHUT DOWN RELAY
DESCRIPTION - PCM OUTPUT.............3
OPERATION
OPERATION - PCM OUTPUT.............3
OPERATION - ASD SENSE - PCM INPUT....4
REMOVAL.............................4
INSTALLATION..........................4
CAMSHAFT POSITION SENSOR
DESCRIPTION
DESCRIPTION - 4.0L....................4
DESCRIPTION - 4.7L....................5
OPERATION
OPERATION - 4.0L.....................5
OPERATION - 4.7L.....................5
REMOVAL
REMOVAL - 4.0L.......................6
REMOVAL - 4.7L.......................7INSTALLATION
INSTALLATION - 4.0L...................8
INSTALLATION - 4.7L...................9
COIL RAIL
DESCRIPTION..........................9
OPERATION...........................10
REMOVAL.............................10
INSTALLATION.........................11
IGNITION COIL
DESCRIPTION.........................11
OPERATION...........................12
REMOVAL.............................12
INSTALLATION.........................12
IGNITION COIL CAPACITOR
DESCRIPTION.........................13
OPERATION...........................13
REMOVAL.............................13
INSTALLATION.........................13
KNOCK SENSOR
DESCRIPTION.........................13
OPERATION...........................13
REMOVAL.............................14
INSTALLATION.........................15
SPARK PLUG
DESCRIPTION.........................15
DIAGNOSIS AND TESTING - SPARK PLUG
CONDITIONS.........................15
REMOVAL.............................18
CLEANING............................18
INSTALLATION.........................18
IGNITION CONTROL
DESCRIPTION
Two different ignition systems are used. One type
of system is for the 4.0L 6±cylinder engine. The other
is for the 4.7L V-8 engine.
OPERATION
The 4.0L 6±cylinder engine uses a one-piece coil
rail containing three independent coils. Although cyl-
inder firing order is the same as 4.0L engines of pre-
vious years, spark plug firing is not. The 3 coils dual-
fire the spark plugs on cylinders 1±6, 2±5 and/or 3±4.
When one cylinder is being fired (on compressionstroke), the spark to the opposite cylinder is being
wasted (on exhaust stroke). The one-piece coil bolts
directly to the cylinder head. Rubber boots seal the
secondary terminal ends of the coils to the top of all
6 spark plugs. One electrical connector (located at
the rear end of the coil rail) is used for all three coils.
The 4.7L V-8 engine uses 8 dedicated and individ-
ually fired coil for each spark plug. Each coil is
mounted directly to the top of each spark plug. A sep-
arate electrical connector is used for each coil.
Because of coil design, spark plug cables (second-
ary cables) are not used on either engine. Adistrib-
utor is not usedwith either the 4.0L or 4.7L
engines.
WJIGNITION CONTROL 8I - 1

The ignition system is controlled by the powertrain
control module (PCM) on all engines.
The ignition system consists of:
²Spark Plugs
²Ignition Coil(s)
²Powertrain Control Module (PCM)
²Crankshaft Position Sensor
²Camshaft Position Sensor
²The MAP, TPS, IAC and ECT also have an effect
on the control of the ignition system.
SPECIFICATIONS
ENGINE FIRING ORDER - 4.0L 6-CYLINDER
ENGINEENGINE FIRING ORDERÐ4.7L V-8 ENGINE
IGNITION COIL RESISTANCE - 4.0L ENGINE
PRIMARY RESISTANCE 21-27ÉC (70-80ÉF)
0.71 - 0.88 Ohms
IGNITION COIL RESISTANCEÐ4.7L V-8
ENGINE
PRIMARY RESISTANCE
21-27ÉC (70-80ÉF)SECONDARY
RESISTANCE 21-27ÉC
(70-80ÉF)
0.6 - 0.9 Ohms 6,000 - 9,000 Ohms
IGNITION TIMING
All ignition timing functions are controlled by the
Powertrain Control Module (PCM). Mechanical
adjustments are not needed and can't be made.
On the 4.0L 6±cylinder engine, do not attempt to
rotate the oil pump drive to adjust timing. This
adjustment is used for fuel synchronization after
camshaft position sensor replacement.
8I - 2 IGNITION CONTROLWJ
IGNITION CONTROL (Continued)

SPARK PLUGS
ENGINE PLUG TYPE ELECTRODE GAP
4.0L 6-CYL. RC12ECC 0.89 mm (.035 in.)
4.7L V-8 (Exc. HO) RC12MCC4 1.01 mm (.040 in.)
4.7L V-8 High
Output (HO)RC7PYCB4 1.01 mm (.040 in.)
TORQUE - IGNITION SYSTEM
DESCRIPTION N-m Ft. Lbs. In. Lbs.
Crankshaft Position Sensor
Bolts - 4.0L Engine7- 60
Crankshaft Position Sensor
Bolt - 4.7L V-8 Engine28 21 -
Camshaft Position
Sensor±to±base bolts - 4.0L
Engine2- 15
Camshaft Position Sensor
Bolt - 4.7L V-8 Engine12 - 106
Oil Pump Drive Hold-down
Bolt - 4.0L Engine23 17 -
Ignition Coil Rail Mounting
Bolts - 4.0L Engine29 - 250
Ignition Coil Mounting Nut -
4.7L V-8 Engine8- 70
* Knock Sensor Bolt - 4.7L
HO V-8 Engine*20 *15 -
Spark Plugs - 4.0L Engine 35-41 26-30 -
Spark Plugs - 4.7L V-8
Engine24-30 18-22 -
* Do not apply any sealant,
thread-locker or adhesive to
bolts. Poor sensor
performance may result.
Refer to Removal / Installation
for additional information.
AUTO SHUT DOWN RELAY
DESCRIPTION - PCM OUTPUT
The 5±pin, 12±volt, Automatic Shutdown (ASD)
relay is located in the Power Distribution Center
(PDC). Refer to label on PDC cover for relay location.
OPERATION
OPERATION - PCM OUTPUT
The ASD relay supplies battery voltage (12+ volts)
to the fuel injectors and ignition coil(s). With certain
emissions packages it also supplies 12±volts to the
oxygen sensor heating elements.
The ground circuit for the coil within the ASD
relay is controlled by the Powertrain Control Module
(PCM). The PCM operates the ASD relay by switch-
ing its ground circuit on and off.
WJIGNITION CONTROL 8I - 3
IGNITION CONTROL (Continued)