standard factory-installed equipment on this model.
Electrically heated outside rear view mirrors are
available facory-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:

• Outside mirror heating grid

• Rear glass heating grid

• Rear window defogger relay

• Rear 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, the use of a
DRB scan tool and the proper Diagnostic Procedures
manual are recommended.

The other electronic modules that may affect power

lock system operation are as follows:

• Body Control Module (BCM) - Refer to Body

Control Module in the Description and Operation
section of Group 8E - Instrument Panel Systems for
more information.

• Driver Door Module (DDM) - Refer to Door

Module in the Power Lock System section of Group
8P - Power Lock Systems.

• Passenger Door Module (PDM) - Refer to

Door Module in the Power Lock System section of
Group 8P - Power Lock Systems.

Refer to Rear Window Defogger and Power

Mirrors in the Contents of Group 8W - Wiring Dia-
grams for complete circuit diagrams. Following are
general descriptions of the major components in the
power lock system.

ELECTRICALLY HEATED SYSTEMS

8N - 1

OPERATION

The rear window defogger system is controlled by a

momentary switch that is integral to the heating and
air conditioning control unit located in the center
stack area of the instrument panel. A Light-Emitting
Diode (LED) in the switch button will light to indi-
cate when the rear window defogger system is turned
on. The BCM, which contains the rear window defog-
ger system timer and control logic, monitors the sta-
tus 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 also sends a defogger switch sta-
tus message to the DDM and the PDM over the PCI
data bus. The DDM and PDM respond to the defog-
ger switch status messages by energizing or de-ener-
gizing the battery current feed to their respective
outside 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.

OUTSIDE MIRROR HEATING GRID

DESCRIPTION

Electrically heated outside rear view mirrors are

standard equipment on this model. These mirrors
feature an electric heating grid located behind the
mirror glass of each power operated outside rear
view mirror. These heating grids consist of a single
resistor wire routed in a grid-like pattern and cap-
tured between two thin sheets of plastic. When elec-
trical current is passed through the resistor wire, it
produces enough heat energy to clear the outside
mirror glass of ice, snow or fog. Battery current is
directed to the outside mirror heating grid only when
the rear window defogger switch is in the On posi-
tion.

If the outside mirror heating grids and the rear

window heating grid are all inoperative, refer to
Rear Window Defogger System in the Diagnosis
and Testing section of this group for diagnosis. If the

outside mirror heating grids are inoperative, but the
rear window heating grid is operating as designed,
refer to Power Mirror in the Diagnosis and Testing
section of Group 8T - Power Mirror Systems for diag-
nosis of the outside 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 sec-
tion of Group 8T - Power Mirror Systems for the ser-
vice procedures.

OPERATION

The outside mirror heating grids are energized and

de-energized by the Driver Door Module (DDM) and
the Passenger Door Module (PDM) based upon the
rear window defogger switch status. The Body Con-
trol Module (BCM) monitors the rear window defog-
ger 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 Programmable
Communications Interface data bus. The DDM and
PDM respond to the defogger switch status messages
by energizing or de-energizing the battery current
feed to their respective outside rear view mirror
heating grids.

REAR GLASS HEATING 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 Rear Glass Heating Grid Repair in the
Service Procedures section of this group for the
repair procedures.

8N - 2

ELECTRICALLY HEATED SYSTEMS

DESCRIPTION AND OPERATION (Continued)

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).

REAR WINDOW DEFOGGER SWITCH

DESCRIPTION

The rear window defogger switch is integral to the

heating and air conditioning control unit, which is
located in the instrument panel center stack below
the radio receiver. This momentary switch provides a
hard wired ground signal to the Body Control Module
(BCM) each time it is depressed. A Light Emitting
Diode (LED) in the push button for the rear window
defogger switch illuminates to indicate when the rear
window defogger system is turned on.

The rear window defogger switch and the rear win-

dow

defogger

switch

LED

indicator

cannot

repaired and, if faulty or damaged, the entire heating
and air conditioning control unit must be replaced.
Refer to Heater-A/C Control in the Removal and
Installation section of Group 24 - Heating and Air
Conditioning for the service procedures.

OPERATION

When the rear window defogger switch push but-

ton is depressed, it momentarily closes the rear win-
dow defogger switch sense circuit for the BCM to
ground. The BCM monitors the rear window defogger
switch sense circuit. Each time the BCM rear win-
dow defogger timer and logic circuitry sees another
input from the switch, it toggles a control output to
the rear window defogger relay. Energizing the rear
window defogger relay provides electrical current to
the rear window defogger grid and to the LED indi-
cator in the switch, which lights to indicate when the
defogger system is turned on. A dedicated fuse in the
junction block protects the rear window defogger
relay output circuit to the LED indicator.

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 SYSTEM

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS,

REFER

GROUP

PASSIVE

RESTRAINT SYSTEMS BEFORE ATTEMPTING ANY
STEERING

WHEEL,

STEERING

COLUMN,

INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.

For complete circuit diagrams, refer to Rear Win-

dow Defogger in the Contents of Group 8W - Wir-
ing Diagrams. The operation of the electrically
heated rear window defogger system can be con-
firmed 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

ELECTRICALLY HEATED SYSTEMS

8N - 3

DESCRIPTION AND OPERATION (Continued)

Content .. 141 142 143 144 ..