exj 8n, JEEP Manuals, Electronic Service Manual (jeep cherokee xj do 2000)
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XJ
ELECTRICALLY HEATED SYSTEMS
8N - 1
ELECTRICALLY HEATED SYSTEMS
TABLE OF CONTENTS
page
page
1
8
REAR WINDOW DEFOGGER SYSTEM
TABLE OF CONTENTS
page
page
GENERAL INFORMATION
DESCRIPTION AND OPERATION
DIAGNOSIS AND TESTING
SERVICE PROCEDURES
REMOVAL AND INSTALLATION
GENERAL INFORMATION
REAR WINDOW DEFOGGER SYSTEM
The rear window defogger system will only operate
when the ignition switch is in the On position. When
the defogger switch is in the On position, an electric
heater grid on the rear window glass is energized.
Vehicles with the heated mirror options also have
heater grids located behind the outside rear view
mirror glass. Each of these grids produce heat to help
clear the rear window glass and outside rear view
mirrors of ice, snow, or fog.
The defogger system is controlled by a switch
installed in the instrument panel accessory switch
bezel, which is located near the bottom of the instru-
ment panel center bezel area, below the heater and
air conditioner controls. An amber indicator lamp in
the switch button will light to indicate when the
defogger system is turned on. The instrument cluster
circuitry, which contains the defogger system timer
logic, monitors the state of the defogger switch
through a hard-wired input. The instrument cluster
circuitry
INTRODUCTION
An electrically heated rear window defogger and
electrically heated outside rear view mirrors are
available factory-installed options on this model.
Refer to 8W-48 - Rear Window Defogger and 8W-62 -
Power Mirrors in Group 8W - Wiring Diagrams for
complete circuit descriptions and diagrams.
NOTE: This group covers both Left-Hand Drive
(LHD) and Right-Hand Drive (RHD) versions of this
model. Whenever required and feasible, the RHD
versions of affected vehicle components have been
constructed as mirror-image of the LHD versions.
While most of the illustrations used in this group
represent only the LHD version, the diagnostic and
service procedures outlined can generally be
applied to either version. Exceptions to this rule
have been clearly identified as LHD or RHD, if a
special illustration or procedure is required.
controls
the
defogger
system
through
a
hard-wired control output to the defogger relay.
The defogger system will be automatically turned
off after a programmed time interval of about ten
minutes. After the initial time interval has expired, if
8N - 2
ELECTRICALLY HEATED SYSTEMS
XJ
GENERAL INFORMATION (Continued)
the defogger switch is turned on again during the
same ignition cycle, the defogger system will auto-
matically 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 instru-
ment panel switch. Following are general descrip-
tions of the major components in the defogger
system. Refer to the owner’s manual in the vehicle
glove box for more information on the features, use
and operation of the defogger system.
window heating grid is operating as designed, refer
to Power Mirror in the Diagnosis and Testing section
of Group 8T - Power Mirror Systems for diagnosis of
the mirror heating grids.
The heating grid behind each outside mirror glass
cannot be repaired and, if faulty or damaged, the
entire power mirror unit must be replaced. Refer to
Power Mirror in the Removal and Installation section
of Group 8T - Power Mirror Systems for the service
procedures.
DEFOGGER SWITCH
The rear window defogger switch is installed in the
instrument panel accessory switch bezel, which is
located near the bottom of the instrument panel cen-
ter bezel area, below the heater and air conditioner
controls. The momentary-type switch provides a
hard-wired ground signal to the instrument cluster
each time it is depressed. The instrument cluster
rear window defogger timer and logic circuitry
responds by energizing or de-energizing the rear win-
dow defogger relay.
Energizing the rear window defogger relay pro-
vides electrical current to the rear window defogger
grid and, if the vehicle is so equipped, the outside
rear view mirror heating grids. An amber indicator
lamp in the defogger switch, which lights to indicate
when the defogger system is turned On, is also pow-
ered by the defogger relay output.
The defogger switch illumination lamp and indica-
tor lamp bulbs are serviceable. The defogger switch
cannot be repaired and, if faulty or damaged, it must
be replaced.
DESCRIPTION AND OPERATION
REAR GLASS HEATING GRID
The heated rear window glass has two electrically
conductive vertical bus bars and a series of horizon-
tal grid lines made of a silver-ceramic material,
which is baked on and bonded to the inside surface of
the glass. The grid lines and bus bars comprise a
parallel electrical circuit.
When the rear window defogger switch is placed in
the On position, electrical current is directed to the
rear window grid lines through the bus bars. The
grid lines heat the rear window to clear the surface
of fog or snow. Protection for the heated grid circuit
is provided by a fuse in the Power Distribution Cen-
ter (PDC).
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 clean-
ing the glass or removing foreign materials, decals,
or stickers from the glass. Normal glass cleaning sol-
vents or hot water used with rags or toweling is rec-
ommended.
A repair kit is available to repair the grid lines and
bus
INSTRUMENT CLUSTER
The instrument cluster is an electromechanical
unit that contains integrated circuitry and internal
programming to perform a variety of functions. The
instrument cluster circuitry monitors hard-wired
switch inputs, as well as message inputs received
from other vehicle electronic control modules on the
Chrysler Collision Detection (CCD) data bus network.
The instrument cluster uses these many inputs
along with its internal programming and integral
timer and logic circuitry to perform the functions of
the rear window defogger timer on this model. The
instrument cluster circuitry also has a self-diagnostic
capability. Refer to Instrument Cluster in Group 8E -
Instrument Panel Systems for more information on
this feature.
However, there are no diagnostics available for the
rear window defogger timer and logic circuitry.
Therefore, the diagnosis for this system consists of
confirming the presence of a rear window defogger
switch input signal at the instrument cluster connec-
tor, and the resulting rear window defogger relay
bars,
or
to
reinstall
the
heated
glass
pigtail
wires.
OUTSIDE MIRROR HEATING GRID
Vehicles equipped with the optional heated mirror
package have an electric heating grid located behind
the mirror glass of each outside rear view mirror.
The heated mirrors are controlled by the rear win-
dow defogger switch. Electrical current is directed to
the heating grid inside the mirror only when the rear
window defogger switch is in the On position.
If the outside mirror heating grids and the rear
window heating grid are all inoperative, diagnosis of
the rear window defogger system should be per-
formed as described in this group. If the outside mir-
ror
heating
grids
are
inoperative,
but
the
rear
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ELECTRICALLY HEATED SYSTEMS
8N - 3
DESCRIPTION AND OPERATION (Continued)
control output signal at the defogger relay. For diag-
nosis of the CCD data bus and the data bus message
inputs, a DRB scan tool and the proper Diagnostic
Procedures manual are recommended.
Refer to Instrument Cluster in Group 8E - Instru-
ment Panel Systems for the service procedures for
the instrument cluster. The rear window defogger
timer and logic circuitry cannot be adjusted or
repaired and, if faulty or damaged, the instrument
cluster assembly must be replaced.
DEFOGGER RELAY
The rear window defogger relay is a International
Standards Organization (ISO)-type relay. The rear
window defogger relay is a electromechanical device
that switches fused battery current to the rear glass
and outside mirror heating grids, and the indicator
lamp of the defogger switch, when the instrument
cluster rear window defogger timer and logic cir-
cuitry grounds the relay coil. See Defogger Relay in
the Diagnosis and Testing section of this group for
more information.
The rear window defogger relay is located in the
junction block, on the right cowl side inner panel
below the instrument panel in the passenger com-
partment. The rear window defogger relay cannot be
repaired
Fig. 1 Rear Window Glass Grid Test
1 – TERMINAL “A”
2 – TERMINAL “B”
3 – FEED WIRE
4 – MID-POINT “C” (TYPICAL)
5 – HEATED REAR WINDOW DEFOGGER GRID
6 – GROUND WIRE
The above checks will confirm system operation.
Illumination of the defogger switch indicator lamp
means that there is electrical current available at the
output of the defogger relay, but does not confirm
that the electrical current is reaching the rear glass
heating grid lines.
If the defogger system does not operate, the prob-
lem should be isolated in the following manner:
(1) Confirm that the ignition switch is in the On
position.
(2) Ensure that the rear glass heating grid feed
and ground wires are connected to the glass. Confirm
that the ground wire has continuity to ground.
(3) Check the fuses in the Power Distribution Cen-
ter (PDC) and in the junction block. The fuses must
be tight in their receptacles and all electrical connec-
tions must be secure.
When the above steps have been completed and the
rear glass or outside rear view mirror heating grid is
still
and,
if
faulty
or
damaged,
it
must
be
replaced.
DIAGNOSIS AND TESTING
DEFOGGER SYSTEM
For circuit descriptions and diagrams, refer to
8W-48 - Rear Window Defogger or 8W-62 Power Mir-
rors in Group 8W - Wiring Diagrams. The operation
of the electrically heated rear window defogger sys-
tem can be confirmed in one of the following man-
ners:
1. Turn the ignition switch to the On position.
While monitoring the instrument panel voltmeter, set
the defogger switch in the On position. When the
defogger switch is turned On, a distinct voltmeter
needle deflection should be noted.
2. Turn the ignition switch to the On position. Set
the defogger switch in the On position. The rear win-
dow defogger operation can be checked by feeling the
rear window or outside rear view mirror glass. A dis-
tinct difference in temperature 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.
inoperative,
one
or
more
of
the
following
is
faulty:
²
Defogger switch
²
Defogger relay
²
Instrument cluster circuitry
Rear 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)
²
²
Outside rear view mirror heating grid.
If setting the defogger switch to the On position
produces a severe voltmeter deflection, check for a
short circuit between the defogger relay output and
the rear glass or outside rear view mirror heating
grids.
8N - 4
ELECTRICALLY HEATED SYSTEMS
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DIAGNOSIS AND TESTING (Continued)
REAR GLASS HEATING GRID
For circuit descriptions and diagrams, refer to
8W-48 - Rear Window Defogger in Group 8W - Wir-
ing Diagrams. To detect breaks in the grid lines, the
following procedure is required:
(1) Turn the ignition switch to the On position. Set
the defogger switch in the On position. The indicator
lamp should light. If OK, go to Step 2. If not OK, see
the Defogger Relay diagnosis in this group.
(2) Using a 12-volt DC voltmeter, contact the ver-
tical bus bar on the right side of the vehicle with the
negative lead. With the positive lead, contact the ver-
tical bus bar on the left side of the vehicle. The volt-
meter should read battery voltage. If OK, go to Step
3. If not OK, repair the open circuit to the defogger
relay as required.
(3) With the negative lead of the voltmeter, contact
a good body ground point. The voltage reading should
not change. If OK, go to Step 4. If not OK, repair the
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. 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 bus bar. A
reading of ten to fourteen volts indicates a break
between midpoint C and the right side bus bar. Move
the positive lead on the grid line towards the break
and the voltage reading will change as soon as the
break is crossed.
(3) Check for continuity between the ground cir-
cuit terminal and the rear window defogger switch
sense circuit terminal on the back of the defogger
switch housing (Fig. 2). There should be momentary
continuity as the defogger switch button is depressed,
and then no continuity. If OK, see the diagnosis for
the Instrument Cluster in this group. If not OK,
replace the faulty switch.
SWITCH POSITION
CONTINUITY BETWEEN
OFF
LAMPS
ON
MOMENTARY 1 AND 2
ILLUMINATION LAMP
1 AND 4
INDICATOR LAMP
1 AND 3
Fig. 2 Defogger Switch Continuity
DEFOGGER RELAY
DEFOGGER SWITCH
For circuit descriptions and diagrams, refer to
8W-48 - Rear Window Defogger in Group 8W - Wir-
ing Diagrams.
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
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.
RELAY TEST
The defogger relay (Fig. 3) is located in the junc-
tion block, on the right cowl side inner panel below
the instrument panel in the passenger compartment.
Remove the 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
DEPLOYMENT
AND
POSSIBLE
PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable. Remove the accessory switch bezel from the
instrument panel and unplug the defogger switch
wire harness connector.
(2) Check for continuity between the ground cir-
cuit cavity of the defogger switch wire harness con-
nector and a good ground. There should be
continuity. If OK, go to Step 3. If not OK, repair the
open circuit as required.
10 ohms. If OK, go to
Step 3. If not OK, replace the faulty relay.
6
XJ
ELECTRICALLY HEATED SYSTEMS
8N - 5
DIAGNOSIS AND TESTING (Continued)
(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, see the Relay Circuit Test in this
group. If not OK, replace the faulty relay.
is turned On. Be certain that you depress the defog-
ger switch at least twice to confirm that the system
is turned on during this test. If OK, go to Step 5. If
not OK, repair the open circuit to the instrument
cluster as required.
(5) The coil battery terminal (86) is connected to
the electromagnet in the relay. It is connected to
fused ignition switch output voltage and should be
hot when the ignition switch is in the On position.
Check for battery voltage at the cavity for relay ter-
minal 86 with the ignition switch in the On position.
If OK, see the diagnosis for Instrument Cluster in
this group. If not OK, repair the open circuit to the
fuse in the junction block as required.
INSTRUMENT CLUSTER
Before performing this test, complete the Defogger
Switch and the Defogger Relay tests as described in
this group. For circuit descriptions and diagrams,
refer to 8W-48 - Rear Window Defogger in Group 8W
- Wiring Diagrams.
TERMINAL LEGEND
NUMBER
IDENTIFICATION
30
COMMON FEED
85
COIL GROUND
86
COIL BATTERY
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
87
NORMALLY OPEN
87A
NORMALLY CLOSED
Fig. 3 Defogger 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 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.
(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 rear glass and outside rear view mirror heat-
ing grids and the defogger switch indicator lamp.
There should be continuity between the cavity for
relay terminal 87 and the rear window defogger relay
output circuit cavities of the rear glass heating grid
connector, both outside rear view mirror heating grid
connectors, and the defogger switch connector at all
times. If OK, go to Step 4. If not OK, repair the open
circuit(s) as required.
(4) The coil ground terminal (85) is connected to
the electromagnet in the relay. This terminal is pro-
vided with ground by the instrument cluster rear
window defogger timer and logic circuitry to energize
the defogger relay. There should be continuity to
ground at the cavity for relay terminal 85 when the
defogger switch is turned On. However, with the
defogger relay removed, the defogger switch indicator
lamp will not light to show that the defogger system
DEPLOYMENT
AND
POSSIBLE
PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable. Remove the defogger relay from the junction
block and unplug the defogger switch wire harness
connector.
(2) Remove the instrument cluster from the instru-
ment panel. Refer to Instrument Cluster in Group 8E
- Instrument Panel Systems for the procedures.
(3) Check for continuity between the rear window
defogger switch sense circuit cavity of the right
instrument cluster wire harness connector (connector
B) and a good ground. There should be no continuity.
If OK, go to Step 4. If not OK, repair the short circuit
as required.
(4) Check for continuity between the rear window
defogger switch sense circuit cavities of the right
instrument cluster wire harness connector (connector
B) and the defogger switch wire harness connector.
There should be continuity. If OK, go to Step 5. If not
OK, repair the open circuit as required.
(5) Check for continuity between the rear window
defogger relay control circuit cavity of the right
instrument cluster wire harness connector (connector
B) and a good ground. There should be no continuity.
If OK, go to Step 6. If not OK, repair the short circuit
as required.
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