The document provides information about diagnosing issues with a vehicle's rear window defogger system. It describes the major components of the system, including the rear window glass grid, defogger switch, and defogger relay/timer. It then lists steps to test overall system operation and to isolate problems, such as using a voltmeter to check for breaks in the glass grid lines or testing power supply to the relay.

1. ZJ REAR WINDOW DEFOGGER 8N - 1
REAR WINDOW DEFOGGER
CONTENTS
page page
DIAGNOSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 SERVICE PROCEDURES ................... 4
GENERAL INFORMATION . . . . . . . . . . . . . . . . . . 1
GENERAL INFORMATION
The electrically-heated rear window defogger is A repair kit is available to repair the grid lines and
standard equipment on Grand Cherokee models. Fol- bus bars, or to reinstall the heated glass pigtail
lowing are general descriptions of the major compo- wires.
nents in the rear window defogger system. Refer to
Group 8W - Wiring Diagrams for complete circuit de- DEFOGGER SWITCH
scriptions and diagrams. The rear window defogger switch is mounted in the
right instrument panel switch pod. The switch circuit
REAR WINDOW GLASS GRID is protected by fuse 23 in the fuseblock module. Ac-
The heated rear window glass has two electrically- tuating the switch energizes the relay and electronic
conductive vertical bus bars and a series of horizon- timer. A light-emitting diode (LED) with an amber
tal grid lines made of a silver-ceramic material, lens in the switch illuminates to indicate when the
which is baked on and bonded to the inside surface of
system is turned on. The defogger switch can not be
the glass. The grid lines and bus bars comprise a
repaired. If faulty, the switch must be replaced.
parallel electrical circuit.
When the rear window defogger switch is placed in
DEFOGGER RELAY/TIMER
the ON position, current is directed to the rear win-
The defogger relay/timer is located in the relay cen-
dow grid lines through the bus bars. The grid lines
ter, which is under a cover in the glove box. When
heat the rear window to clear the surface of fog or
snow. Circuit protection for the heated grid circuit is the rear defogger switch is actuated, the rear defog-
provided by a circuit breaker in cavity 28 of the fuse- ger relay is energized. This causes current to flow
block module. through the grid circuit for approximately 10 min-
The grid lines and bus bars are highly resistant to utes, or until the rear window defogger switch or ig-
abrasion. However, it is possible for an open to occur nition switch are turned off. Power for the relay is
in an individual grid line resulting in no current flow protected by fuse 19 in the fuseblock module. The de-
through the line. The grid lines can be damaged or fogger relay/timer can not be repaired and, if faulty,
scraped off with sharp instruments. Care should be must be replaced.
taken in cleaning the glass or removing foreign ma-
terials, decals or stickers. Normal glass cleaning sol-
vents or hot water used with rags or toweling is
recommended.
DIAGNOSIS
SYSTEM TESTS (3) Monitor vehicle voltmeter. With the control
Electrically-heated rear window defogger operation switch ON, a distinct needle deflection should be
can be confirmed in the following manner: noted.
(1) Turn the ignition switch to the ON position. (4) The rear window defogger operation can be
(2) Turn rear window defogger control switch ON. checked by feeling the glass. A distinct difference in

2. 8N - 2 REAR WINDOW DEFOGGER ZJ
temperature between the grid lines and adjacent lead of voltmeter. With positive lead of voltmeter,
clear glass can be detected within 3 to 4 minutes of contact feed side vertical bus bar (point B of Fig. 1).
operation. The voltmeter should read 10-14 volts.
(5) Using a DC voltmeter, contact terminal A (Fig. (3) With negative lead of voltmeter, contact a good
1) (passenger side) with the negative lead, and termi- body ground point. The voltage reading should not
nal B (driver side) with the positive lead. The volt- change. A different reading indicates a poor ground
meter should read 10-14 volts. connection.
(4) Connect negative lead of voltmeter to point A
on ground side bus bar and touch each grid line at
mid-point with positive lead. A reading of approxi-
mately 6 volts indicates a line is good. A reading of
zero volts indicates a break in the grid line between
mid-point C and point B. A reading of 10-14 volts in-
dicates a break between mid-point C and point A.
Move toward break and voltage will change as soon
as break is crossed.
DEFOGGER SWITCH
(1) Remove defogger switch from instrument panel.
Use a jumper wire to apply 12 volts to terminal 1 of
switch (Fig. 2). Using another jumper wire connect
terminal 3 of switch to ground. The indicator lamp
Fig. 1 Rear Window Glass Grid Test
should light. If OK, go to next step. If not OK, re-
Steps 3, 4 or 5 above will confirm system operation. place switch.
Indicator light illumination means that there is (2) Remove jumper wires and connect an ohmme-
power available at the output of the switch, but does ter to terminals 2 and 3 of switch. Push the switch
not confirm that power is reaching the rear window button. Ohmmeter should read less than 1 ohm. If
grid lines. OK, go to next step. If not OK, replace switch.
If the rear window defogger does not operate, the (3) Check defogger switch wiring circuits as fol-
problem should be isolated in the following manner: lows:
(1) Confirm that ignition switch is in ON position. • between switch connector cavity 1 and fuse 23
(2) Ensure that the heated rear window feed and • between switch connector cavity 3 and ground
ground wires are connected to the glass. Confirm • between switch connector cavity 2 and terminal 3
that the ground wire has continuity to ground. of the relay.
(3) Check fuses 19 and 23, and circuit breaker 28 Repair switch wiring shorts or opens as required.
in the fuseblock module. Fuses and circuit breaker
must be tight in their receptacles and all electrical DEFOGGER RELAY
connections must be secure. (1) Remove defogger relay from relay center and
When the above steps have been completed and the turn ignition switch to ON position. Measure voltage
system is still inoperative, one or more of the follow- at relay center cavity for defogger relay terminal 5.
ing is faulty: Meter should show battery voltage. If OK, go to next
• defogger switch step. If not OK, repair circuit to fuse 19 as required.
• relay/timer (2) Measure voltage at relay center cavity for de-
• rear window grid lines (all grid lines would have fogger relay terminal 4. The meter should read bat-
to be broken or one of the feed wires disconnected for tery voltage. If OK, go to next step. If not OK, repair
the entire system to be inoperative). open from circuit breaker 28.
If turning the switch ON produces severe voltmeter (3) Turn ignition switch to OFF position. Measure
deflection, check for a short circuit. resistance between relay center cavity for defogger
relay terminal 1 and left (driver’s) side of defogger
REAR WINDOW GLASS GRID grid. The meter should read zero ohms. If OK, go to
To detect breaks in grid lines, the following proce- next step. If not OK, repair circuit between relay and
dure is required: defogger grid.
(1) Turn ignition switch to the ON position. Turn (4) Measure resistance between relay center cavity
rear defogger switch ON. The indicator lamp should for defogger relay terminal 2 and a good ground. The
light. meter should read zero ohms. If OK, go to next step.
(2) Using a 12-volt DC voltmeter, contact ground If OK, go to next step. If not OK, repair circuit be-
side vertical bus bar (point A of Fig. 1) with negative tween relay center and ground.

3. ZJ REAR WINDOW DEFOGGER 8N - 3
(5) Install defogger relay in relay center. Turn ig- not OK, replace defogger relay.
nition switch to ON position. Measure voltage at re-
lay terminal 3. The meter should read near 5 volts. If
Fig. 2 Defogger Switch Circuit
REAR WINDOW DEFOGGER SYSTEM SCHEMATIC

4. 8N - 4 REAR WINDOW DEFOGGER ZJ
SERVICE PROCEDURES
REAR WINDOW GLASS GRID REPAIRS (7) Apply a thin layer of conductive epoxy to termi-
The repair of grid lines, bus bars or pigtail wires nal or bare wire end of pigtail and place in desired
can be accomplished using the MOPAR Rear Window location. To prevent terminal or pigtail from moving
Defogger Repair Kit (P/N 4267922) or equivalent. while the epoxy is curing, it must be wedged or
clamped.
WARNING: MATERIALS CONTAINED IN REPAIR KIT (8) Carefully remove masking tape from grid line.
MAY CAUSE SKIN OR EYE IRRITATION. CONTAINS
EPOXY RESIN AND AMINE TYPE HARDENER, CAUTION: Do not allow the glass surface to exceed
HARMFUL IF SWALLOWED. AVOID CONTACT WITH 400°F, glass may fracture.
SKIN AND EYES. FOR SKIN, WASH AFFECTED AR-
EAS WITH SOAP AND WATER. DO NOT TAKE IN- (9) Allow epoxy to cure 24 hours at room tempera-
TERNALLY. IF TAKEN INTERNALLY, INDUCE ture or use heat gun with a 260°-371°C (500°-700°F)
VOMITING; CALL A PHYSICIAN IMMEDIATELY. IF IN range for 15 minutes. Hold gun approximately
CONTACT WITH EYES, FLUSH WITH PLENTY OF 254mm (10 inches) from repaired area.
WATER. USE WITH ADEQUATE VENTILATION. DO (10) After conductive epoxy is properly cured re-
NOT USE NEAR FIRE OR FLAME. CONTENTS CON- move wedge or clamp from terminal or pigtail and
TAIN 3% FLAMMABLE SOLVENTS. KEEP OUT OF check operation of rear window defogger. Do not at-
REACH OF CHILDREN. tach connectors until curing is complete.
(1) Mask repair area so that the conductive epoxy DEFOGGER SWITCH REMOVE/INSTALL
can be applied neatly. Extend epoxy application onto (1) Disconnect battery negative cable.
the grid line or the bus bar (Fig. 3) on either side of (2) Remove ash receiver.
the break. (3) Remove 6 screws holding instrument panel cen-
ter bezel (Fig. 4).
Fig. 3 Grid Line Repair (Typical)
(2) Follow instructions in repair kit for preparing
damaged area.
(3) Remove package separator clamp and mix two
conductive epoxy components thoroughly within
packaging. Fold package in half and cut center cor-
ner to dispense epoxy.
(4) For grid line, mask area to be repaired with
masking tape or a template (Fig. 3).
(5) Apply epoxy through slit in masking tape or
template. Overlap both ends of the break by at least
19mm (.75 in.).
(6) For a terminal or pigtail replacement, mask ad-
jacent areas so epoxy can be extended onto line as
well as bus bar. Apply a thin layer of epoxy to area
where terminal or pigtail was fastened and onto ad- Fig. 4 Instrument Panel Center Bezel
jacent grid line. (4) Remove center bezel.

5. ZJ REAR WINDOW DEFOGGER 8N - 5
(5) Remove 2 screws holding dash pad located be-
hind top of center bezel.
(6) Gently pry defroster grille out of dash pad.
(7) Unplug auto head lamp and sun sensors (if
equipped) and set defroster grille aside.
(8) Remove 4 screws in defroster duct opening
holding dash pad (Fig. 5).
Fig. 5 Upper Dash Pad Attaching Screws
(9) Remove 3 screws above instrument panel clus-
ter holding dash pad (Fig. 6). Fig. 7 Lower Instrument Panel Trim
Fig. 6 Remove Screws Holding Dash Pad
(10) Open glove box and remove 2 screws holding
dash pad.
(11) Remove dash pad by pulling up to unsnap end
clips.
(12) With left front door open, remove 1 screw from
the side of the lower instrument panel trim (Fig. 7).
(13) Remove 4 screws holding the steering column
cover (Fig. 8).
(14) Remove 1 screw from bottom of lower instru-
ment panel trim and pull panel off. There is also a Fig. 8 Steering Column Cover and Knee Blocker
clip holding the panel to the instrument panel.
(15) Remove 6 screws holding knee blocker.
(16) Remove steering column retaining nuts.

6. 8N - 6 REAR WINDOW DEFOGGER ZJ
(17) Remove 3 screws holding bottom of bezels (Fig.
9).
Fig. 9 Remove Screws Holding Bottom Of Bezels
(18) Remove 2 screws holding top of end and
switch pod bezels (Fig. 10). The end bezel can now be
removed.
Fig. 11 Left Switch Pod Bezel Screws
Fig. 10 Remove Screws Holding Top of Bezels
(19) Remove 2 screws holding left switch pod bezel
(Fig. 11).
(20) Remove 3 screws holding right switch pod be-
zel (Fig. 12).
Fig. 12 Right Switch Pod Bezel Screws

7. ZJ REAR WINDOW DEFOGGER 8N - 7
(21) Pull switch pod bezel out far enough to remove
switch connectors. Disconnect connectors from each
switch pod and remove bezel (Fig. 13).
Fig. 14 Relay Center Cover
Fig. 13 Rear View Of Switch Pod Bezel
(22) Remove required switch pod attaching screws
and switch pod.
(23) Reverse the removal procedures to install.
Tighten steering column retaining nuts to 12 N⅐m
(105 in. lbs.).
DEFOGGER RELAY/TIMER REMOVE/INSTALL
(1) Open glove box and remove 3 screws holding
relay center cover (Fig. 14).
(2) Remove the red relay from the relay center
(Fig. 15).
(3) Align relay terminals with cavities in relay cen- Fig. 15 Rear Window Defogger Relay
ter and push relay into place.
(4) Re-install relay center cover.