Diagnosis JEEP GRAND CHEROKEE 2002 WJ / 2.G Owners Manual

INSPECTION
For complete circuit diagrams, refer toStarting
Systemin the Contents of Group 8W - Wiring Dia-
grams. Before removing any unit from the starting
system for repair or diagnosis, perform the following
inspections:
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO GROUP 8M - PASSIVE
RESTRAINT SYSTEMS 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.
²Battery- Visually inspect the battery for indi-
cations of physical damage and loose or corroded
cable connections. Determine the state-of-charge and
cranking capacity of the battery. Charge or replace
the battery, if required. Refer toBatteryin the
proper section of Group 8A - Battery for complete ser-
vice information for the battery.
²Ignition Switch- Visually inspect the ignition
switch for indications of physical damage and loose
or corroded wire harness connections. Refer toIgni-
tion Switch and Key Lock Cylinderin the proper
section of Group 8D - Ignition System for complete
service information for the ignition switch.
²Park/Neutral Position Switch- Visually
inspect the park/neutral position switch for indica-
tions of physical damage and loose or corroded wire
harness connections. Refer toPark/Neutral Posi-
tion Switchin the proper section of Group 21 -
Transmission for complete service information for the
park/neutral position switch.
²Starter Relay- Visually inspect the starter
relay for indications of physical damage and loose or
corroded wire harness connections.
²Starter Motor- Visually inspect the starter
motor for indications of physical damage and loose or
corroded wire harness connections.
²Starter Solenoid- Visually inspect the starter
solenoid for indications of physical damage and loose
or corroded wire harness connections.
²Wiring- Visually inspect the wire harnesses for
damage. Repair or replace any faulty wiring, as
required. Refer to the proper section ofGroup 8W -
Wiring Diagramsfor complete service information
and circuit diagrams for the starting system wiring
components.TESTING
COLD CRANKING TEST
For complete circuit diagrams, refer toStarting
Systemin the Contents of Group 8W - Wiring Dia-
grams. The battery must be fully-charged and load-
tested before proceeding. Refer toBatteryin the
Diagnosis and Testing section of Group 8A - Battery
for the procedures.
(1) Connect a suitable volt-ampere tester to the
battery terminals (Fig. 1). See the instructions pro-
vided by the manufacturer of the volt-ampere tester
being used.
(2) Fully engage the parking brake.
(3) Place the automatic transmission gearshift
selector lever in the Park position.
(4) Verify that all lamps and accessories are
turned off.
(5) To prevent the engine from starting, remove
the Automatic ShutDown (ASD) relay. The ASD relay
is located in the Power Distribution Center (PDC), in
the engine compartment. Refer to the fuse and relay
layout label affixed to the underside of the PDC cover
for ASD relay identification and location.
(6) Rotate and hold the ignition switch in the Start
position. Note the cranking voltage and current
(amperage) draw readings shown on the volt-ampere
tester.
(a) If the voltage reads below 9.6 volts, refer to
Starter Motorin the Diagnosis and Testing sec-
tion of this group. If the starter motor is OK, refer
toEngine Diagnosisin the Diagnosis and Testing
section of Group 9 - Engine for further testing of
the engine. If the starter motor is not OK, replace
the faulty starter motor.
Fig. 1 Volts-Amps Tester Connections - Typical
1 - POSITIVE CLAMP
2 - NEGATIVE CLAMP
3 - INDUCTION AMMETER CLAMP
8F - 32 STARTINGWJ
STARTING (Continued)

(b) If the voltage reads above 9.6 volts and the
current (amperage) draw reads below specifica-
tions, refer toFeed Circuit Testin this section.
(c) If the voltage reads 12.5 volts or greater and
the starter motor does not turn, refer toControl
Circuit Testingin this section.
(d) If the voltage reads 12.5 volts or greater and
the starter motor turns very slowly, refer toFeed
Circuit Testin this section.
NOTE: A cold engine will increase the starter cur-
rent (amperage) draw reading, and reduce the bat-
tery voltage reading.
FEED CIRCUIT TEST
The starter feed circuit test (voltage drop method)
will determine if there is excessive resistance in the
high-amperage feed circuit. For complete circuit dia-
grams, refer toStarting Systemin the Contents of
Group 8W - Wiring Diagrams.
When performing these tests, it is important to
remember that the voltage drop is giving an indica-
tion of the resistance between the two points at
which the voltmeter probes are attached.
Example:When testing the resistance of the bat-
tery positive cable, touch the voltmeter leads to the
battery positive cable clamp and the cable connector
at the starter solenoid. If you probe the battery pos-
itive terminal post and the cable connector at the
starter solenoid, you are reading the combined volt-
age drop in the battery positive cable clamp-to-termi-
nal post connection and the battery positive cable.
The following operation will require a voltmeter
accurate to 1/10 (0.10) volt. Before performing the
tests, be certain that the following procedures are
accomplished:
²Battery is fully-charged and load-tested. Refer to
Batteryin the Diagnosis and Testing section of
Group 8A - Battery for the procedures.
²Fully engage the parking brake.
²Place the automatic transmission gearshift selec-
tor lever in the Park position.
²
Verify that all lamps and accessories are turned off.
²To prevent the engine from starting, remove the
Automatic ShutDown (ASD) relay. The ASD relay is
located in the Power Distribution Center (PDC), in
the engine compartment. Refer to the fuse and relay
layout label affixed to the underside of the PDC cover
for ASD relay identification and location.
(1) Connect the positive lead of the voltmeter to
the battery negative terminal post. Connect the neg-
ative lead of the voltmeter to the battery negative
cable clamp (Fig. 2). Rotate and hold the ignition
switch in the Start position. Observe the voltmeter. If
voltage is detected, correct the poor contact between
the cable clamp and the terminal post.(2) Connect the positive lead of the voltmeter to
the battery positive terminal post. Connect the nega-
tive lead of the voltmeter to the battery positive cable
clamp (Fig. 3). Rotate and hold the ignition switch in
the Start position. Observe the voltmeter. If voltage
is detected, correct the poor contact between the
cable clamp and the terminal post.
(3) Connect the voltmeter to measure between the
battery positive terminal post and the starter sole-
noid battery terminal stud (Fig. 4). Rotate and hold
the ignition switch in the Start position. Observe the
voltmeter. If the reading is above 0.2 volt, clean and
tighten the battery cable connection at the solenoid.
Fig. 2 Test Battery Negative Connection Resistance
- Typical
1 - VOLTMETER
2 - BATTERY
Fig. 3 Test Battery Positive Connection Resistance -
Typical
1 - VOLTMETER
2 - BATTERY
WJSTARTING 8F - 33
STARTING (Continued)

Repeat the test. If the reading is still above 0.2 volt,
replace the faulty battery positive cable.
(4) Connect the voltmeter to measure between the
battery negative terminal post and a good clean
ground on the engine block (Fig. 5). Rotate and hold
the ignition switch in the Start position. Observe the
voltmeter. If the reading is above 0.2 volt, clean and
tighten the battery negative cable attachment on the
engine block. Repeat the test. If the reading is still
above 0.2 volt, replace the faulty battery negative
cable.(5) Connect the positive lead of the voltmeter to
the starter housing. Connect the negative lead of the
voltmeter to the battery negative terminal post (Fig.
6). Rotate and hold the ignition switch in the Start
position. Observe the voltmeter. If the reading is
above 0.2 volt, correct the poor starter to engine
block ground contact.
If the resistance tests detect no feed circuit prob-
lems, refer toStarter Motorin the Diagnosis and
Testing section of this group.
CONTROL CIRCUIT TESTING
The starter control circuit components should be
tested in the order in which they are listed, as fol-
lows:
²Starter Relay- Refer toStarter Relayin the
Diagnosis and Testing section of this group for the
procedures.
²Starter Solenoid- Refer toStarter Motorin
the Diagnosis and Testing section of this group for
the procedures.
²Ignition Switch- Refer toIgnition Switch
and Key Lock Cylinderin the Diagnosis and Test-
ing section of Group 8D - Ignition System for the pro-
cedures.
²Park/Neutral Position Switch- Refer to
Park/Neutral Position Switchin the Diagnosis
and Testing section of Group 21 - Transmission for
the procedures.
²Wire harnesses and connections- Refer to
Starting Systemin the Contents of Group 8W -
Wiring Diagrams for complete circuit diagrams.
Fig. 4 Test Battery Positive Cable Resistance -
Typical
1 - BATTERY
2 - VOLTMETER
3 - STARTER MOTOR
Fig. 5 Test Ground Circuit
1 - VOLTMETER
2 - BATTERY
3 - ENGINE GROUND
Fig. 6 Test Starter Ground - Typical
1 - STARTER MOTOR
2 - BATTERY
3 - VOLTMETER
8F - 34 STARTINGWJ
STARTING (Continued)

OPERATION
These starter motors are equipped with a plane-
tary gear reduction (intermediate transmission) sys-
tem. The planetary gear reduction system consists of
a gear that is integral to the output end of the elec-
tric motor armature shaft that is in continual
engagement with a larger gear that is splined to the
input end of the starter pinion gear shaft. This fea-
ture makes it possible to reduce the dimensions of
the starter. At the same time, it allows higher arma-
ture rotational speed and delivers increased torque
through the starter pinion gear to the starter ring
gear.
The starter motors for both engines are activated
by an integral heavy duty starter solenoid switch
mounted to the overrunning clutch housing. This
electromechanical switch connects and disconnects
the feed of battery voltage to the starter motor and
actuates a shift fork that engages and disengages the
starter pinion gear with the starter ring gear.
Both starter motors use an overrunning clutch and
starter pinion gear unit to engage and drive a starter
ring gear that is integral to the torque converter
drive plate mounted on the rear crankshaft flange.
DIAGNOSIS AND TESTING - STARTER MOTOR
Correct starter motor operation can be confirmed
by performing the following free running bench test.
This test can only be performed with the starter
motor removed from the vehicle. Refer toStarting
Systemin the Specifications section of this group for
the starter motor specifications.
(1) Remove the starter motor from the vehicle.
Refer toStarter Motorin the Removal and Instal-
lation section of this group for the procedures.
(2) Mount the starter motor securely in a soft-
jawed bench vise. The vise jaws should be clamped
on the mounting flange of the starter motor. Never
clamp on the starter motor by the field frame.
(3) Connect a suitable volt-ampere tester and a
12-volt battery to the starter motor in series, and set
the ammeter to the 100 ampere scale. See the
instructions provided by the manufacturer of the
volt-ampere tester being used.
(4) Install a jumper wire from the solenoid termi-
nal to the solenoid battery terminal. The starter
motor should operate. If the starter motor fails to
operate, replace the faulty starter motor assembly.
(5) Adjust the carbon pile load of the tester to
obtain the free running test voltage. Refer toStart-
ing Systemin the Specifications section of this
group for the starter motor free running test voltage
specifications.
(6) Note the reading on the ammeter and compare
this reading to the free running test maximum
amperage draw. Refer toStarting Systemin theSpecifications section of this group for the starter
motor free running test maximum amperage draw
specifications.
(7) If the ammeter reading exceeds the maximum
amperage draw specification, replace the faulty
starter motor assembly.
STARTER SOLENOID
This test can only be performed with the starter
motor removed from the vehicle.
(1) Remove the starter motor from the vehicle.
Refer toStarter Motorin the Removal and Instal-
lation section of this group for the procedures.
(2) Disconnect the wire from the solenoid field coil
terminal.
(3) Check for continuity between the solenoid ter-
minal and the solenoid field coil terminal with a con-
tinuity tester (Fig. 7). There should be continuity. If
OK, go to Step 4. If not OK, replace the faulty starter
motor assembly.
(4) Check for continuity between the solenoid ter-
minal and the solenoid case (Fig. 8). There should be
continuity. If not OK, replace the faulty starter motor
assembly.
Fig. 7 Continuity Test Between Solenoid Terminal
and Field Coil Terminal - Typical
1 - SOLENOID
2 - SOLENOID TERMINAL
3 - OHMMETER
4 - FIELD COIL TERMINAL
Fig. 8 Continuity Test Between Solenoid Terminal
1 - SOLENOID
2 - SOLENOID TERMINAL
3 - OHMMETER
8F - 36 STARTINGWJ
STARTER MOTOR (Continued)

(8) Remove the starter motor from the engine com-
partment.
INSTALLATION
(1) Position the starter motor in the engine com-
partment.
(2) Reconnect the solenoid terminal wire harness
connector to the connector receptacle on the starter
solenoid. Always support the starter motor during
this process, do not let the starter motor hang from
the wire harness.
(3) Install the battery cable eyelet onto the sole-
noid battery terminal. Always support the starter
motor during this process, do not let the starter
motor hang from the wire harness.
(4) Install and tighten the nut that secures the
battery cable eyelet to the solenoid battery terminal.
Tighten the nut to 11.3 N´m (100 in. lbs.). Always
support the starter motor during this process, do not
let the starter motor hang from the wire harness.
(5) Position the starter motor to the front of the
automatic transmission torque converter housing and
loosely install both the upper and lower mounting
screws.
(6) Tighten the lower (forward facing) starter
motor mounting screw. On 4.0L engines, tighten the
screw to 41 N´m (30 ft. lbs.). On 4.7L engines, tighten
the screw to 54 N´m (40 ft. lbs.).(7) Tighten the upper (rearward facing) starter
mounting screw. Tighten the screw to 54 N´m (40 ft.
lbs.).
(8) Lower the vehicle.
(9) Reconnect the battery negative cable.
STARTER MOTOR RELAY
DESCRIPTION
The starter relay is an electromechanical device
that switches battery current to the pull-in coil of the
starter solenoid when the ignition switch is turned to
the Start position. The starter relay is located in the
Power Distribution Center (PDC), in the engine com-
partment. See the fuse and relay layout label affixed
to the inside surface of the PDC cover for starter
relay identification and location.
The starter relay is a International Standards
Organization (ISO) micro-relay. Relays conforming to
the ISO specifications have common physical dimen-
sions, current capacities, terminal patterns, and ter-
minal 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 starter 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 mov-
able) electrical contacts. The movable (common feed)
relay contact is held against one of the fixed contacts
(normally closed) by spring pressure. When the elec-
tromagnetic 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 con-
nected in parallel with the electromagnetic coil in the
relay, and helps to dissipate voltage spikes that are
produced when the coil is de-energized.
DIAGNOSIS AND TESTING - STARTER RELAY
The starter relay (Fig. 13) is located in the Power
Distribution Center (PDC), in the engine compart-
ment. Refer to the fuse and relay layout label affixed
to the underside of the PDC cover for starter relay
identification and location. For complete circuit dia-
grams, refer toStarting Systemin the Contents of
Group 8W - Wiring Diagrams.
Fig. 12 Starter Wire Harness Remove/Install - 4.7L
Engine
1 - SOLENOID BATTERY TERMINAL EYELET
2 - NUT
3 - SOLENOID TERMINAL CONNECTOR
4 - BATTERY STARTER AND GENERATOR WIRE HARNESS
5 - RETAINERS
8F - 38 STARTINGWJ
STARTER MOTOR (Continued)

(1) Remove the starter relay from the PDC. Refer
toStarter Relayin the Removal and Installation
section of this group 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 starter solenoid field coils. There should be
continuity between the cavity for relay terminal 87
and the starter solenoid terminal at all times. If OK,
go to Step 4. If not OK, repair the open circuit to the
starter solenoid as required.
(4) The coil battery terminal (86) is connected to
the electromagnet in the relay. It is energized when
the ignition switch is held in the Start position.
Check for battery voltage at the cavity for relay ter-
minal 86 with the ignition switch in the Start posi-tion, and no voltage when the ignition switch is
released to the On position. If OK, go to Step 5. If
not OK, check for an open or short circuit to the igni-
tion switch and repair, if required. If the circuit to
the ignition switch is OK, refer toIgnition Switch
and Key Lock Cylinderin the Diagnosis and Test-
ing section of Group 8D - Ignition System for testing
of the ignition switch.
(5) The coil ground terminal (85) is connected to
the electromagnet in the relay. It is grounded
through the park/neutral position switch only when
the gearshift selector lever is in the Park or Neutral
positions. Check for continuity to ground at the cav-
ity for relay terminal 85. If not OK, check for an
open or short circuit to the park/neutral position
switch and repair, if required. If the circuit to the
park/neutral position switch is OK, refer toPark/
Neutral Position Switchin the Diagnosis and
Testing section of Group 21 - Transmission for testing
of the park/neutral position switch.
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the cover from the Power Distribution
Center (PDC) (Fig. 14) .
Fig. 13 Starter Relay
30 - COMMON FEED
85 - COIL GROUND
86 - COIL BATTERY
87 - NORMALLY OPEN
87A - NORMALLY CLOSED
Fig. 14 Power Distribution Center
1 - RIGHT FENDER
2 - BATTERY
3 - POWER DISTRIBUTION CENTER
4 - COVER
WJSTARTING 8F - 39
STARTER MOTOR RELAY (Continued)

HEATED SYSTEMS
TABLE OF CONTENTS
page page
HEATED GLASS........................... 1
HEATED MIRRORS......................... 8HEATED SEAT SYSTEM..................... 9
HEATED GLASS
TABLE OF CONTENTS
page page
HEATED GLASS
DESCRIPTION - REAR WINDOW DEFOGGER . . 1
OPERATION - REAR WINDOW DEFOGGER....2
DIAGNOSIS AND TESTING - REAR WINDOW
DEFOGGER SYSTEM...................2
REAR WINDOW DEFOGGER GRID
DESCRIPTION..........................3
OPERATION............................3
DIAGNOSIS AND TESTING - REAR WINDOW
DEFOGGER GRID......................3
STANDARD PROCEDURE - REAR GLASS
HEATING GRID REPAIR.................4
REAR WINDOW DEFOGGER RELAY
DESCRIPTION..........................5OPERATION............................5
DIAGNOSIS AND TESTING - REAR WINDOW
DEFOGGER RELAY.....................5
REMOVAL.............................6
INSTALLATION..........................6
REAR WINDOW DEFOGGER SWITCH
DESCRIPTION..........................6
OPERATION............................7
DIAGNOSIS AND TESTING - REAR WINDOW
DEFOGGER SWITCH...................7
REMOVAL.............................7
HEATED GLASS
DESCRIPTION - REAR WINDOW DEFOGGER
An electrically heated rear window defogger is
standard factory-installed equipment on this model.
Electrically heated outside rear view mirrors are
available factory-installed optional equipment. When
the rear window defogger system is turned on, elec-
tric heater grids on the liftgate flip-up glass and
behind both outside rear view mirror glasses are
energized. These electric heater grids produce heat to
help clear the rear window glass and the outside rear
view mirrors of ice, snow, or fog. The rear window
defogger system control circuit uses ignition switched
battery current, so the system will only operate when
the ignition switch is in the On position.
This group covers the following components of the
rear window defogger system:
²Rear glass heating grid
²Rear window defogger relay²Rear window defogger switch.
Certain functions and features of the rear window
defogger system rely upon resources shared with
other electronic modules in the vehicle over the Pro-
grammable Communications Interface (PCI) data bus
network. The PCI data bus network allows the shar-
ing 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 fea-
ture capabilities. For diagnosis of these electronic
modules or of the PCI data bus network, use a
DRBIIItscan tool and (Refer to Appropriate Diagnos-
tic Information).
The other electronic modules that may affect
proper system operation are:
²Body Control Module (BCM)- Refer to Elec-
tronic Control Modules for more information.
²Driver Door Module (DDM)- Refer to Elec-
tronic Control Modules for more information.
WJHEATED SYSTEMS 8G - 1

²Passenger Door Module (PDM)- Refer to
Electronic Control Modules for more information.
OPERATION - REAR WINDOW DEFOGGER
The rear window defogger system is controlled by a
momentary switch that is integral to the a/c heater
control located in the center stack area of the instru-
ment panel. A Light-Emitting Diode (LED) in the
switch button will light to indicate when the rear
window defogger system is turned on. The BCM,
which contains the rear window defogger system
timer and control logic, monitors the status of the
defogger switch through a hard-wired input. The
BCM then sends control outputs through a hard
wired circuit to energize or de-energize the defogger
relay.
The electrically heated outside rear view mirror
heating grids are also controlled by the rear window
defogger switch. When the BCM receives an input
from the switch, it sends a defogger switch status
message to the DDM and the PDM over the PCI data
bus. The DDM and PDM respond to the defogger
switch status messages by energizing or de-energiz-
ing the battery current feed to their respective out-
side rear view mirror heating grids.
The rear window defogger system will be automat-
ically turned off after a programmed time interval of
about ten minutes. After the initial time interval has
expired, if the defogger switch is turned on again
during the same ignition cycle, the defogger system
will automatically turn off after about five minutes.
The defogger system will automatically shut off if the
ignition switch is turned to the Off position, or it can
be turned off manually by depressing the rear win-
dow defogger switch again.
See the owner's manual in the vehicle glove box for
more information on the features, use and operation
of the rear window defogger system.
DIAGNOSIS AND TESTING - REAR WINDOW
DEFOGGER SYSTEM
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN AN ACCIDENTAL
AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.For complete circuit diagrams, (Refer to Appropri-
ate Wiring Information). The operation of the electri-
cally heated rear window defogger system can be
confirmed in one of the following manners:
1. Turn the ignition switch to the On position.
While monitoring the instrument panel voltmeter,
depress the rear window defogger switch to the On
position. When the rear window defogger switch is
turned On, a distinct voltmeter needle deflection
should be noted.
2. Turn the ignition switch to the On position.
Depress the rear window defogger switch to the On
position. The rear window defogger operation can be
checked by feeling the rear window or outside rear
view mirror glass. A distinct difference in tempera-
ture between the grid lines and the adjacent clear
glass or the mirror glass can be detected within three
to four minutes of operation.
3. Using a 12-volt DC voltmeter, contact the rear
glass heating grid terminal A (right side) with the
negative lead, and terminal B (left side) with the pos-
itive lead (Fig. 1). The voltmeter should read battery
voltage.
The above checks will confirm rear window defog-
ger system operation. Illumination of the rear win-
dow defogger switch LED indicator means that there
is battery current available at the output of the rear
window defogger relay, but does not confirm that bat-
tery current is reaching the rear glass heating grid
lines.
If the rear window defogger system does not oper-
ate, the problem should be isolated in the following
manner:
Fig. 1 REAR WINDOW GLASS GRID TEST
1 - TERMINAL ªAº
2 - TERMINAL ªBº
3 - FEED WIRE
4 - MID-POINT ªCº (TYPICAL)
5 - HEATED REAR WINDOW DEFOGGER GRID
6 - GROUND WIRE
8G - 2 HEATED GLASSWJ
HEATED GLASS (Continued)

(1) Confirm that the ignition switch is in the On
position.
(2) Ensure that the rear glass heating grid feed
and ground terminals are connected to the glass.
Confirm that the ground wire has continuity to
ground.
(3) Check the fused B(+) fuse in the Power Distri-
bution Center (PDC). The fuse must be tight in its
receptacles and all electrical connections must be
secure.
When the above steps have been completed and the
rear glass heating grid is still inoperative, one or
more of the following is faulty:
²Rear window defogger switch
²Rear window defogger relay
²Body Control Module (BCM)
²Rear window grid lines (all grid lines would
have to be broken or one of the feed wires discon-
nected for the entire system to be inoperative).
When the above steps have been completed and the
heated mirror glass heating grid is still inoperative,
one or more of the following is faulty:
²Body Control Module (BCM)
²Programmable Communications Interface (PCI)
data bus
²Driver Door Module (DDM) or Passenger Door
Module (PDM)
²Outside rear view mirror heating grids.
If turning the rear window defogger system on pro-
duces a severe voltmeter deflection, check for a short
circuit between the rear window defogger relay out-
put and the rear glass heating grid.
REAR WINDOW DEFOGGER
GRID
DESCRIPTION
The electrically heated rear window glass is stan-
dard equipment on this model. The liftgate flip-up
glass has two electrically conductive vertical bus bars
and a series of horizontal grid lines made of a silver-
ceramic material, which is baked on and bonded to
the inside surface of the glass. These grid lines and
the bus bars comprise a parallel electrical circuit. A
spade type terminal near the top of each bus bar
accept the connectors from the two coiled liftgate
wire harness take outs.
The grid lines and bus bars are highly resistant to
abrasion. However, it is possible for an open circuit
to occur in an individual grid line, resulting in no
current flow through the line. The grid lines can be
damaged or scraped off with sharp instruments. Care
should be taken when cleaning the glass or removing
foreign materials, decals, or stickers from the glass.Normal glass cleaning solvents or hot water used
with rags or toweling is recommended.
A repair kit is available to repair the grid lines and
bus bars, or to reinstall the heated glass terminals.
(Refer to 8 - ELECTRICAL/HEATED GLASS/REAR
WINDOW DEFOGGER GRID - STANDARD PROCE-
DURE)
OPERATION
The rear glass heating grid is energized and de-en-
ergized by the rear window defogger relay. The Body
Control Module (BCM) monitors the rear window
defogger switch. When the BCM receives an input
from the switch, it energizes or de-energizes the rear
window defogger relay through a hard wired control
output. The rear defogger relay switches fused bat-
tery current to the rear window grid lines through
the bus bars. The grid lines heat the rear window
glass to clear the surface of ice, snow or fog. Protec-
tion for the rear glass heating grid circuit is provided
by a fuse in the Power Distribution Center (PDC).
DIAGNOSIS AND TESTING - REAR WINDOW
DEFOGGER GRID
For complete circuit diagrams, (Refer to Appropri-
ate Wiring Information). To detect breaks in the rear
glass heating grid lines, the following procedure is
required:
(1) Turn the ignition switch to the On position.
Turn the rear window defogger system on. The rear
window defogger switch LED indicator should light.
If OK, go to Step 2. If not OK, (Refer to 8 - ELEC-
TRICAL/HEATED GLASS/REAR WINDOW DEFOG-
GER RELAY - DIAGNOSIS AND TESTING).
(2) Using a 12-volt DC voltmeter, contact the rear
glass heating grid vertical bus bar on the right side
of the vehicle with the negative lead. With the posi-
tive lead, contact the rear glass heating grid vertical
bus bar on the left side of the vehicle. The voltmeter
should read battery voltage. If OK, go to Step 3. If
not OK, repair the open rear window defogger relay
output circuit to the rear window defogger relay as
required.
(3) With the positive voltmeter lead still contacting
the rear glass heating grid vertical bus bar on the
left side of the vehicle, move the negative lead of the
voltmeter to a good body ground point. The voltage
reading should not change. If OK, go to Step 4. If not
OK, repair the ground circuit to ground as required.
(4) Connect the negative lead of the voltmeter to
the right side bus bar and touch each grid line at
midpoint C with the positive lead (Fig. 2). A reading
of approximately six volts indicates a line is good. A
reading of zero volts indicates a break in the grid
line between midpoint C and the left side rear glass
heating grid bus bar. A reading of ten to fourteen
WJHEATED GLASS 8G - 3
HEATED GLASS (Continued)

not attach the wire harness connectors until the cur-
ing process is complete.
(11) Check the operation of the rear glass heating
grid.
REAR WINDOW DEFOGGER
RELAY
DESCRIPTION
The rear window defogger relay is an electrome-
chanical device that switches fused battery current to
the rear glass heating grid and the Light-Emitting
Diode (LED) indicator of the rear window defogger
switch, when the Body Control Module (BCM) rear
window defogger timer and logic circuitry grounds
the relay coil. The rear window defogger relay is
located in the junction block, under the left end of
the instrument panel in the passenger compartment.
The rear window defogger relay is a International
Standards Organization (ISO) relay. Relays conform-
ing to the ISO specifications have common physical
dimensions, current capacities, terminal patterns,
and terminal functions.
The rear window defogger 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 mov-
able) electrical contacts. The movable (common feed)
relay contact is held against one of the fixed contacts
(normally closed) by spring pressure. When the elec-
tromagnetic 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 con-
nected in parallel with the electromagnetic coil in the
relay, and helps to dissipate voltage spikes that are
produced when the coil is de-energized.
DIAGNOSIS AND TESTING - REAR WINDOW
DEFOGGER RELAY
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN AN ACCIDENTAL
AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
RELAY TEST
The rear window defogger relay (Fig. 4) is located
in the junction block, under the left end of the instru-
ment panel in the passenger compartment. Remove
the rear window defogger relay from the junction
block to perform the following tests:
(1) 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 2. If not OK, replace the faulty relay.
(2) Resistance between terminals 85 and 86 (elec-
tromagnet) should be 75   10 ohms. If OK, go to Step
3. If not OK, replace the faulty relay.
(3) 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, refer to theRelay Circuit Test.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
fused B(+) circuit to the Power Distribution Center
(PDC) fuse 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.
Fig. 4 REAR WINDOW DEFOGGER RELAY
TERMINAL LEGEND
NUMBER IDENTIFICATION
30 COMMON FEED
85 COIL GROUND
86 COIL BATTERY
87 NORMALLY OPEN
87A NORMALLY CLOSED
WJHEATED GLASS 8G - 5
REAR WINDOW DEFOGGER GRID (Continued)