Chrysler 300M, Dodge Interpid. Manual - part 74

the BCM failed to complete the circuit to ground
required to energize the EBL relay coil (Fig. 3).

(2) Using a DC voltmeter with a 0-15 volt range,

connect the negative lead to a known good vehicle
electrical ground.

(3) Touch the positive bus bar and check voltage.

The voltage should be above 11 volts. Push the Rear
Window Defogger button to turn off the indicator.
The measured voltage should be 0 volts. If these volt-
ages are correct then the problem is with the Rear
Window Grid or Grid ground electrical connection.
(Refer to 8 - ELECTRICAL/HEATED GLASS/REAR
WINDOW DEFOGGER GRID - DIAGNOSIS AND
TESTING) If there is no voltage to the rear window
defogger grid when the system is ON, (Refer to 8 -
ELECTRICAL/HEATED GLASS - DIAGNOSIS AND
TESTING

FUSE AND

ELECTRICAL SHORT

TEST).

DIAGNOSIS AND TESTING - FUSE AND
ELECTRICAL SHORT TEST

(1) Stop the engine.
(2) Check the fuse supplying power to the rear

glass grid relay. If the fuse is good, (Refer to 8 -
ELECTRICAL/HEATED

GLASS/REAR

WINDOW

DEFOGGER RELAY - DIAGNOSIS AND TESTING).
If the fuse is open, then go to Step 3.

(3) Locate the ground lug that connects the nega-

tive lead of the rear window grid to ground. Remove
the screw holding the ground lug and isolate it from
any vehicle ground.

(4) Connect one lead of an ohmmeter to the nega-

tive ground lug of the rear window grid (with the lug
still not connected to a vehicle ground), and check
the resistance to a known good vehicle ground. If the
ohmmeter indicates less than 10 ohms, then the rear
window defogger grid is shorting to the vehicle
ground, then go to Step 5. If the ohmmeter indicates
more than 100 ohms of resistance, then go to Step 6.

(5) Disconnect the rear window defogger grid volt-

age feed wire from the vehicle harness. If the ohm-
meter still indicates less than 10 ohms, then the rear
window defogger grid is shorting to the vehicle
ground and must be replaced. If the ohmmeter indi-
cates more than 100 ohms of resistance with the grid
voltage feed wire disconnected, then go to Step 6.

(6) There is a problem with the circuits that con-

nect to the rear window defogger relay. Refer to the
appropriate wiring information for circuit descrip-
tions. Check wiring with an ohmmeter to verify
proper wiring connections to the rear window defog-
ger relay. If no problems are found, then replace the
fuse and try running the system.

REAR WINDOW DEFOGGER
GRID

DIAGNOSIS AND TESTING - REAR WINDOW
DEFOGGER GRID

The horizontal grid line and vertical bus bar line is

printed and fired on the inside surface of the rear
window glass. These comprise an electrical circuit.
The electrically conductive lines are composed of a
silver ceramic material which when fired on glass
becomes bonded to the glass and is highly resistant
to abrasion. It is possible, however, that a break may
occur in an individual grid line resulting in no cur-
rent flow through the line. To detect breaks in grid
lines, the following procedure is required:

(1) Stop the engine. Connect the negative lead of a

0-25 volt range voltmeter to a known good vehicle
electrical ground.

(2) Start the engine and push the rear window

defogger button to turn on the system.

(3) Touch the ground side (point B) of the Rear

Window Defogger Grid (Fig. 4). The voltage mea-
sured should be below 1 volt. If the voltage is greater
than 1 volt then check the voltage on each grid line
at the Mid-Point with the positive lead. If the voltage
is not approximately 6 volts or half the voltage mea-

Fig. 3 REAR WINDOW DEFOGGER SYSTEM

SCHEMATIC

1 - BCM AND BUTTON LED RELAY CONTROL LINE (MANUAL
TEMPERATURE CONTROL ONLY)
2 - VEHICLE VOLTAGE SUPPLY
3 - GROUND CONNECTOR
4 - REAR WINDOW GRID LINE STRUCTURE
5 - POINT B
6 - MIDPOINT C (TYPICAL)
7 - POINT A
8 - POWER CONNECTOR

HEATED GLASS

8G - 3

HEATED GLASS (Continued)

sured on the positive rear window grid bus bar, then
the grid line is bad. The break in the grid can be
found by moving the probe along the line until the
voltage changes. The area where the voltage changes
is where the open circuit is.

STANDARD PROCEDURE - REAR WINDOW
DEFOGGER GRID REPAIR

The repair of the grid lines or the terminal is pos-

sible using the Mopar

t Repair Package or equivalent.

(1) Mask the repair area so conductive epoxy can

be extended onto the line or the bus bar (Fig. 5).

(2) Follow the instructions in the repair kit for

preparing the damaged area.

(3) Remove the package separator clamp and mix

the plastic conductive epoxy thoroughly. Fold in half
and cut the center corner to dispense the epoxy.

(4) For grid line repair, mark off the area to be

repaired with masking tape or a template (Fig. 5).

(5) Apply conductive epoxy through the slit in the

masking tape. Overlap both ends of the break by 19
mm (3/4 inch).

(6) For a terminal or pigtail replacement, mask

adjacent areas so the epoxy can be extended onto the
line as well as the bus bar. Apply a thin layer of
epoxy to the area where the terminal was fastened
and to the adjacent line.

(7) Apply a thin layer of conductive epoxy on the

terminal and place terminal on desired location. To
prevent the terminal from moving while the epoxy is
curing, it must be wedged or clamped.

(8) Carefully remove the masking tape from the

grid line.

CAUTION: Do not allow the glass surface to exceed
204°C (400°F), glass may fracture.

(9) Allow epoxy to cure 24 hours at room tempera-

ture or use a heat gun with a 260°-371°C (500°-
700°F)

range

for

minutes.

Hold

the

gun

approximately 254 mm (10 inches) from the repaired
area.

(10) After the conductive epoxy is properly cured

remove the wedge from the terminal and check the
rear window defogger operation. Do not attach the
connectors until curing is complete.

WARNING: REPAIR KIT MAY CAUSE SKIN OR EYE
IRRITATION. CONTAINS EPOXY RESIN AND AMINE
TYPE

HARDENER,

HARMFUL

SWALLOWED.

AVOID CONTACT WITH SKIN AND EYES. FOR SKIN,
WASH AFFECTED AREAS WITH SOAP AND WATER.
DO NOT TAKE INTERNALLY. IF TAKEN INTER-
NALLY, INDUCE VOMITING; CALL A PHYSICIAN
IMMEDIATELY. IF IN CONTACT WITH EYES, FLUSH
WITH PLENTY OF WATER. USE WITH ADEQUATE
VENTILATION. DO NOT USE NEAR FIRE OR FLAME.
CONTENTS CONTAIN 3 PERCENT FLAMMABLE
SOLVENTS.
KEEP OUT OF REACH OF CHILDREN.

Fig. 4 GRID LINE TEST

1 - VOLTAGE FEED A
2 - BUS BARS
3 - REAR WINDOW DEFOGGER
4 - MIDPOINT C
5 - GROUND B
6 - VOLTMETER
7 - REAR SHELF
8 - CHMSL TRIM COVER

Fig. 5 GRID LINE REPAIR

1 - BREAK
2 - GRID LINE
3 - MASKING TAPE

8G - 4

HEATED GLASS

REAR WINDOW DEFOGGER GRID (Continued)

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 right rear trunk area behind the car-
peting.

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

(1) Stop the engine. Connect the negative lead of a

0-15 volt range voltmeter to a known good vehicle
electrical ground.

(2) Reconnect rear window grid connections if dis-

connected for the Fuse and Electrical Short Test.
Start the engine check the voltages present at the
rear window defogger relay and rear window defog-
ger grid (Fig. 3). Refer to the Rear Window Defogger
Relay Test table for diagnosis.

REAR WINDOW DEFOGGER RELAY TEST

POTENTIAL PROBLEM

SYSTEM
ON OR OFF
WITH
ENGINE
RUNNING

VOLTAGE AT REAR WINDOW

DEFOGGER RELAY POINT TO

GOOD VEHICLE GROUND

VOLTAGE AT
REAR WINDOW
DEFOGGER
GRID TO GOOD
VEHICLE
GROUND

NO PROBLEM. VOLTAGES AS
EXPECTED WITH THE SYSTEM
OFF.

OFF

THAN

NO PROBLEM. VOLTAGES AS
EXPECTED WITH THE SYSTEM
ON.

THAN

LESS

THAN

1.0

THAN

LESS

THAN

1.0

RELAY CONTACTS NOT CLOSING.
REPLACE RELAY.

THAN

LESS

THAN

1.0

WIRING OPEN BETWEEN BODY
CONTROL MODULE AND REAR
WINDOW DEFOGGER RELAY, OR,
DEFECTIVE BODY CONTROL
MODULE.

THAN

HEATED GLASS

8G - 5

POTENTIAL PROBLEM

SYSTEM
ON OR OFF
WITH
ENGINE
RUNNING

VOLTAGE AT REAR WINDOW

DEFOGGER RELAY POINT TO

GOOD VEHICLE GROUND

VOLTAGE AT
REAR WINDOW
DEFOGGER
GRID TO GOOD
VEHICLE
GROUND

POOR CONNECTION BETWEEN
PIN 3 OF RELAY AND POSITIVE
CONNECTION ON REAR WINDOW
DEFOGGER GRID CIRCUIT.

THAN

LESS

THAN

1.0

POOR CONNECTION TO GROUND
ON NEGATIVE SIDE OF REAR
WINDOW DEFOGGER GRID.

THAN

LESS

THAN

1.0

THAN

POOR WIRING CONNECTION
BETWEEN PINS 1 TO 2 OF THE
REAR WINDOW DEFOGGER
RELAY.

THAN

OPEN FUSE OR OPEN WIRING
CONNECTION TO PIN 1 OF REAR
WINDOW DEFOGGER RELAY.

RELAY CONTACTS SHORTED.
REPLACE RELAY. REAR WINDOW
DEFOGGER WILL NOT TURN OFF.

OFF

THAN

REMOVAL

(1) Disconnect the battery negative remote cable

from the remote ground post (Fig. 6).

(2) Open the trunk. Remove the carpeting fasten-

ers from the right rear panel and pull the trunk car-
peting away.

(3) Remove the relay fastener screw and unplug

the relay.

(4) Remove the relay from vehicle.

INSTALLATION

(1) Plug the relay into the wire harness connector.
(2) Install the relay fastener screw.
(3) Place the carpet back into position and install

the fasteners.

(4) Connect the negative battery cable to the

remote ground post.

(5) Test the rear window defogger system for

proper operation.

Fig. 6 NEGATIVE BATTERY CABLE REMOTE

TERMINAL

1 - RIGHT STRUT TOWER
2 - AIR CLEANER INLET TUBE
3 - REMOTE TERMINAL

8G - 6

HEATED GLASS

REAR WINDOW DEFOGGER RELAY (Continued)

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