2002 JEEP GRAND CHEROKEE rear light

repaired and, if faulty or damaged, the entire a/c
heater control must be replaced. (Refer to 24 - HEAT-
ING & AIR CONDITIONING/CONTROLS/A/C
HEATER CONTROL - REMOVAL)
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.
DIAGNOSIS AND TESTING - REAR WINDOW
DEFOGGER SWITCH
For complete circuit diagrams, refer to the Appro-
priate Wiring Information.
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.
(1) Disconnect and isolate the battery negative
cable. Remove the a/c heater control from the instru-
ment panel and disconnect the 11-way (manual tem-
perature control) or 16-way (automatic zone control)
instrument panel wire harness connector from the a/c
heater control receptacle.
(2) Check for continuity between the ground cir-
cuit cavity of the 11-way or 16-way instrument panel
wire harness connector for the a/c heater control and
a good ground. There should be continuity. If OK, go
to Step 3. If not OK, repair the open ground circuit to
ground as required.
(3) Connect two jumper wires to the a/c heater
control 11-way or 16-way connector receptacle. Con-
nect one jumper from the ground circuit terminal inthe 11-way or 16-way a/c heater control connector
receptacle to a good ground. Connect the other
jumper from the fused rear window defogger relay
output circuit terminal of the 11-way or 16-way con-
nector receptacle to a 12-volt battery feed. The rear
window defogger switch LED indicator should light.
If OK, go to Step 4. If not OK, replace the faulty a/c
heater control.
(4) Check for continuity between the ground cir-
cuit and rear window defogger switch sense circuit
terminals of the 11-way or 16-way a/c heater control
connector receptacle. There should be momentary
continuity as the rear window defogger switch push
button is depressed, and then no continuity. If OK, go
to Step 5. If not OK, replace the faulty a/c heater
control.
(5) Disconnect the 22-way instrument panel wire
harness connector from the Body Control Module
(BCM) connector receptacle. Check for continuity
between the rear window defogger switch sense cir-
cuit cavity of the 11-way or 16-way instrument panel
wire harness connector for the a/c heater control and
a good ground. There should be no continuity. If OK,
go to Step 6. If not OK, repair the shorted rear win-
dow defogger switch sense circuit as required.
(6) Check for continuity between the rear window
defogger switch sense circuit cavities of the 11-way or
16-way instrument panel wire harness connector for
the a/c heater control and the 22-way instrument
panel wire harness connector for the BCM. There
should be continuity. If OK, refer to (Refer to 8 -
ELECTRICAL/HEATED GLASS/REAR WINDOW
DEFOGGER RELAY - DIAGNOSIS AND TESTING).
REMOVAL
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.
(Refer to 24 - HEATING & AIR CONDITIONING/
CONTROLS/A/C HEATER CONTROL - REMOVAL)
WJHEATED GLASS 8G - 7
REAR WINDOW DEFOGGER SWITCH (Continued)

(14) If a plus (+) or a minus (-) is displayed next to
degree number, and/or the degree displayed is not
zero, loosen but do not remove hold-down clamp bolt.
Rotate oil pump drive until IN RANGE appears on
screen. Continue to rotate oil pump drive until
achieving as close to 0É as possible.
The degree scale on SET SYNC screen of DRB is
referring to fuel synchronization only.It is not
referring to ignition timing.Because of this, do
not attempt to adjust ignition timing using this
method. Rotating oil pump drive will have no effect
on ignition timing. All ignition timing values are con-
trolled by powertrain control module (PCM).
(15) Tighten hold-down clamp bolt to 23 N´m (17
ft. lbs.) torque.
INSTALLATION - 4.7L
The Camshaft Position Sensor (CMP) on the 4.7L
V±8 engine is bolted to the front/top of the right cyl-
inder head (Fig. 10).
(1) Clean out machined hole in cylinder head.
(2) Apply a small amount of engine oil to sensor
o-ring.
(3) Install sensor into cylinder head with a slight
rocking action. Do not twist sensor into position as
damage to o-ring may result.
CAUTION: Before tightening sensor mounting bolt,
be sure sensor is completely flush to cylinder head.
If sensor is not flush, damage to sensor mounting
tang may result.
(4) Install mounting bolt and tighten to 12 N´m
(106 in. lbs.) torque.
(5) Connect electrical connector to sensor.
(6) Lower vehicle.
COIL RAIL
DESCRIPTION
A one-piece coil rail assembly containing three
individual coils is used on the 4.0L 6±cylinder engine
(Fig. 11). The coil rail must be replaced as one
assembly. The bottom of the coil is equipped with 6
individual rubber boots (Fig. 11) to seal the 6 spark
plugs to the coil. Inside each rubber boot is a spring.
The spring is used for a mechanical contact between
the coil and the top of the spark plug. These rubber
boots and springs are a permanent part of the coil
and are not serviced separately.
(1) The coil is bolted directly to the cylinder head
(Fig. 12). One electrical connector (located at rear of
coil) is used for all three coils.
Fig. 11 Ignition Coil AssemblyÐ4.0L 6±Cylinder
Engine
1 - CYL. #6
2 - CYL. #5
3 - CYL. #4
4 - CYL. #3
5 - CYL. #2
6 - CYL. #1
7 - COILS (3)
8 - MOUNTING BOLTS (4)
9 - BOLT BASES (4)
10 - RUBBER BOOTS (6)
Fig. 12 Coil LocationÐ4.0L Engine
1 - COIL RAIL
2 - COIL MOUNTING BOLTS (4)
3 - COIL
4 - COIL ELECTRICAL CONNECTION
WJIGNITION CONTROL 8I - 9
CAMSHAFT POSITION SENSOR (Continued)

INSTALLATION
4.7L High-Output Engine Only
NOTE: The left sensor is identified by an identifica-
tion tag (LEFT). It is also identified by a larger bolt
head. The Powertrain Control Module (PCM) must
have and know the correct sensor left/right posi-
tions. Do not mix the sensor locations.
(1) Thoroughly clean knock sensor mounting holes.
(2) Install sensors (Fig. 22) into cylinder block.
NOTE: Over or under tightening the sensor mount-
ing bolts will affect knock sensor performance, pos-
sibly causing improper spark control. Always use
the specified torque when installing the knock sen-
sors. The torque for the knock senor bolt is rela-
tively light for an 8mm bolt.
NOTE: Note foam strip on bolt threads. This foam is
used only to retain the bolts to sensors for plant
assembly. It is not used as a sealant. Do not apply
any adhesive, sealant or thread locking compound
to these bolts.
(3) Install and tighten mounting bolts.Bolt
torque is critical.Refer to torque specification.
(4) Install intake manifold. Refer to Engine sec-
tion.
(5) Connect knock sensor pigtail wiring harness to
engine wiring harness near right / rear of intake
manifold (Fig. 23).
SPARK PLUG
DESCRIPTION
Both the 4.0L 6-cylinder and the 4.7L V-8 engine
use resistor type spark plugs. Standard 4.7L V-8
engines are equipped with ªfired in suppressor sealº
type spark plugs using a copper core ground elec-
trode. High-Output (H.O.) 4.7L V-8 engines are
equipped with unique plugs using a platinum rivet
located on the tip of the center electrode.
Because of the use of an aluminum cylinder head
on the 4.7L engine, spark plug torque is very critical.
To prevent possible pre-ignition and/or mechanical
engine damage, the correct type/heat range/number
spark plug must be used.Do not substitute any
other spark plug on the 4.7L H.O. engine. Seri-
ous engine damage may occur.
Plugs on both engines have resistance values rang-
ing from 6,000 to 20,000 ohms (when checked with at
least a 1000 volt spark plug tester).Do not use an
ohmmeter to check the resistance values of thespark plugs. Inaccurate readings will result.
Remove the spark plugs and examine them for
burned electrodes and fouled, cracked or broken por-
celain insulators. Keep plugs arranged in the order
in which they were removed from the engine. A sin-
gle plug displaying an abnormal condition indicates
that a problem exists in the corresponding cylinder.
Replace spark plugs at the intervals recommended in
Group O, Lubrication and Maintenance.
EXCEPT 4.7L H.O. ENGINE :Spark plugs that
have low mileage may be cleaned and reused if not
otherwise defective, carbon or oil fouled. Also refer to
Spark Plug Conditions.4.7L H.O. ENGINE :Never
clean spark plugs on the 4.7L H.O. engine. Damage
to the platinum rivet will result.
CAUTION: EXCEPT 4.7L H.O. ENGINE : Never use a
motorized wire wheel brush to clean the spark
plugs. Metallic deposits will remain on the spark
plug insulator and will cause plug misfire.
H.O. Gap Adjustment:If equipped with the 4.7L
H.O. engine, do not use a wire-type gapping tool as
damage to the platinum rivet on the center electrode
may occur. Use a tapered-type gauge (Fig. 24).
DIAGNOSIS AND TESTING - SPARK PLUG
CONDITIONS
NORMAL OPERATING
The few deposits present on the spark plug will
probably be light tan or slightly gray in color. This is
evident with most grades of commercial gasoline
Fig. 24 PLUG GAP - 4.7L H.O.
1 - TAPER GAUGE
WJIGNITION CONTROL 8I - 15
KNOCK SENSOR (Continued)

INSTRUMENT CLUSTER
DESCRIPTION
The instrument cluster for this model is an Elec-
troMechanical Instrument Cluster (EMIC) module
that is located in the instrument panel above the
steering column opening, directly in front of the
driver (Fig. 1). The remainder of the EMIC, including
the mounts and the electrical connections, are con-
cealed behind the cluster bezel. The EMIC gauges
and indicators are protected by an integral clear
plastic cluster lens, and are visible through a dedi-
cated hooded opening in the instrument panel top
pad. Just behind and integral to the cluster lens are
the cluster hood and cluster mask, which are con-
structed of molded black plastic. Two cluster masks
are used: A base version features a black matte face
and no trim ring around the perimeter of each gauge
opening, while a premium version features a black
matte face and a raised trim ring around the perim-
eter of each gauge opening. The cluster hood serves
as a visor and shields the face of the cluster from
ambient light and reflections to reduce glare, while
the cluster mask serves to separate and define the
individual gauges of the EMIC. On the lower edge of
the cluster lens just right of the speedometer, the
black plastic odometer/trip odometer switch button
protrudes through dedicated holes in the cluster
mask and the cluster lens. The molded plastic EMIC
lens, hood and mask unit has four integral mounting
tabs, two tabs extend down vertically from the lower
edge of the unit and two tabs extend horizontally
rearward from the upper surface of the hood. The
two lower mounting tabs are used to secure theEMIC to the molded plastic instrument panel cluster
carrier with two screws, while the two upper tabs are
secured to the underside of the hood formation of the
instrument panel top pad with two screws. A single
molded connector receptacle located on the EMIC
electronic circuit board is accessed from the back of
the cluster housing and is connected to the vehicle
electrical system through a single dedicated take out
and connector of the instrument panel wire harness.
The cluster mask features two large round open-
ings near its center through which the two major
gauges are visible, and two smaller round openings
stacked at the outboard side of each of the large
openings through which the four minor gauges are
visible. The cluster mask and the dial faces of the
gauges are laminated plastic units. The dark, visible
surface of the mask and the gauge dial faces are the
outer layer or overlay, which is translucent. The
darkness of this outer layer prevents the cluster from
appearing too cluttered or busy by concealing the
cluster indicators that are not illuminated, while the
translucence of this layer allows those indicators and
icons that are illuminated to be readily visible. The
underlying layer of the cluster mask overlay is
opaque and allows light from the various indicators
behind it to be visible through the outer layer of the
mask and gauge dial faces only through predeter-
mined cutouts. On the base instrument clusters the
graphics, increments, and numerals on the gauge
faces are also translucent and illuminated from
behind, while the orange gauge pointers are illumi-
nated internally. On the premium instrument clus-
ters the graphics, increments, numerals and gauge
needles are opaque while the remainder of the gauge
faces are translucent and illuminated from behind by
an electro-luminescent lamp. The EMIC electronic
circuitry is protected by a molded plastic rear cover
that features several round access holes for service of
the incandescent cluster indicator and illumination
lighting lamps and a large rectangular access hole
for the EMIC connector receptacle. The EMIC rear
cover is secured to the cluster housing with screws,
while the cluster lens, hood, and mask unit is
secured to the cluster housing with several integral
plastic latch features.
Twelve versions of the EMIC module are offered on
this model, two base and ten premium. These ver-
sions accommodate all of the variations of optional
equipment and regulatory requirements for the vari-
ous markets in which the vehicle will be offered. This
module utilizes integrated circuitry and information
carried on the Programmable Communications Inter-
face (PCI) data bus network for control of all gauges
and many of the indicators. (Refer to 8 - ELECTRI-
CAL/ELECTRONIC CONTROL MODULES/COM-
MUNICATION - DESCRIPTION - PCI BUS). The
Fig. 1 Instrument Cluster
1 - INSTRUMENT PANEL TOP PAD HOOD FORMATION
2 - INSTRUMENT CLUSTER
3 - CLUSTER BEZEL
8J - 2 INSTRUMENT CLUSTERWJ

EMIC also uses several hard wired inputs in order to
perform its many functions. The EMIC module incor-
porates a blue-green digital Vacuum Fluorescent Dis-
play (VFD) for displaying odometer and trip
odometer information.
The EMIC houses six analog gauges and has pro-
visions for up to twenty indicators (Fig. 2). The
EMIC includes the following analog gauges:
²Coolant Temperature Gauge
²Fuel Gauge
²Oil Pressure Gauge
²Speedometer
²Tachometer
²Voltage Gauge
Some of the EMIC indicators are automatically
configured when the EMIC is connected to the vehi-
cle electrical system for compatibility with certain
optional equipment or equipment required for regula-
tory purposes in certain markets. While each EMIC
may have provisions for indicators to support every
available option, the configurable indicators will not
be functional in a vehicle that does not have the
equipment that an indicator supports. The EMIC
includes provisions for the following indicators (Fig.
2):
²Airbag Indicator (with Airbags only)
²Antilock Brake System (ABS) Indicator
²Brake Indicator
²Check Gauges Indicator
²Coolant Low Indicator (with Diesel Engine
only)
²Cruise Indicator
²Four-Wheel Drive Part Time Indicator
(with Selec-Trac NVG-242 Transfer Case only)
²Front Fog Lamp Indicator (with Front Fog
Lamps only)
²High Beam Indicator
²Low Fuel Indicator
²Malfunction Indicator Lamp (MIL)
²Overdrive-Off Indicator (except Diesel
Engine)
²Rear Fog Lamp Indicator (with Rear Fog
Lamps only)
²Seatbelt Indicator
²Sentry Key Immobilizer System (SKIS)
Indicator
²Transmission Overtemp Indicator (except
Diesel Engine)²Turn Signal (Right and Left) Indicators
²Wait-To-Start Indicator (with Diesel Engine
only)
²Water-In-Fuel Indicator (with Diesel Engine
only)
Many indicators in the EMIC are illuminated by a
dedicated Light Emitting Diode (LED) that is sol-
dered onto the EMIC electronic circuit board. The
LEDs are not available for service replacement and,
if damaged or faulty, the entire EMIC must be
replaced. Base cluster illumination is accomplished
by dimmable incandescent back lighting, which illu-
minates the gauges for visibility when the exterior
lighting is turned on. Premium cluster illumination
is accomplished by a dimmable electro-luminescent
lamp that is serviced only as a unit with the EMIC.
Each of the incandescent bulbs is secured by an inte-
gral bulb holder to the electronic circuit board from
the back of the cluster housing. The incandescent
bulb/bulb holder units are available for service
replacement.
Hard wired circuitry connects the EMIC to the
electrical system of the vehicle. These hard wired cir-
cuits are integral to several wire harnesses, which
are routed throughout the vehicle and retained by
many different methods. These circuits may be con-
nected to each other, to the vehicle electrical system
and to the EMIC through the use of a combination of
soldered splices, splice block connectors, and many
different types of wire harness terminal connectors
and insulators. Refer to the appropriate wiring infor-
mation. The wiring information includes wiring dia-
grams, proper wire and connector repair procedures,
further details on wire harness routing and reten-
tion, as well as pin-out and location views for the
various wire harness connectors, splices and grounds.
The EMIC modules for this model are serviced only
as complete units. The EMIC module cannot be
adjusted or repaired. If a gauge, an LED indicator,
the VFD, the electronic circuit board, the circuit
board hardware, the cluster overlay, the electro-lumi-
nescent lamp (premium model only) or the EMIC
housing are damaged or faulty, the entire EMIC mod-
ule must be replaced. The cluster lens, hood and
mask unit and the individual incandescent lamp
bulbs with holders are available for service replace-
ment.
WJINSTRUMENT CLUSTER 8J - 3
INSTRUMENT CLUSTER (Continued)

OPERATION
The ElectroMechanical Instrument Cluster (EMIC)
is designed to allow the vehicle operator to monitor
the conditions of many of the vehicle components and
operating systems. The gauges and indicators in the
EMIC provide valuable information about the various
standard and optional powertrains, fuel and emis-
sions systems, cooling systems, lighting systems,
safety systems and many other convenience items.
The EMIC is installed in the instrument panel so
that all of these monitors can be easily viewed by the
vehicle operator when driving, while still allowing
relative ease of access for service. The microproces-
sor-based EMIC hardware and software uses various
inputs to control the gauges and indicators visible on
the face of the cluster. Some of these inputs are hard
wired, but most are in the form of electronic mes-
sages that are transmitted by other electronic mod-ules over the Programmable Communications
Interface (PCI) data bus network. (Refer to 8 -
ELECTRICAL/ELECTRONIC CONTROL MOD-
ULES/COMMUNICATION - OPERATION).
The EMIC microprocessor smooths the input data
using algorithms to provide gauge readings that are
accurate, stable and responsive to operating condi-
tions. These algorithms are designed to provide
gauge readings during normal operation that are con-
sistent with customer expectations. However, when
abnormal conditions exist, such as low or high bat-
tery voltage, low oil pressure or high coolant temper-
ature, the algorithm can drive the gauge pointer to
an extreme position and the microprocessor turns on
the Check Gauges indicator to provide a distinct
visual indication of a problem to the vehicle operator.
The instrument cluster circuitry also sends electronic
chime tone request messages over the PCI data bus
to the Body Control Module (BCM) when it monitors
Fig. 2 EMIC Gauges & Indicators
1 - BRAKE INDICATOR 15 - TRANSMISSION OVERTEMP INDICATOR
2 - REAR FOG LAMP INDICATOR 16 - PART TIME 4WD INDICATOR
3 - WATER-IN-FUEL INDICATOR 17 - CHECK GAUGES INDICATOR
4 - VOLTAGE GAUGE 18 - ENGINE TEMPERATURE GAUGE
5 - LEFT TURN INDICATOR 19 - ODOMETER/TRIP ODOMETER SWITCH BUTTON
6 - TACHOMETER 20 - ODOMETER/TRIP ODOMETER DISPLAY
7 - HIGH BEAM INDICATOR 21 - WAIT-TO-START INDICATOR
8 - AIRBAG INDICATOR 22 - OVERDRIVE-OFF INDICATOR
9 - SPEEDOMETER 23 - SEATBELT INDICATOR
10 - RIGHT TURN INDICATOR 24 - ABS INDICATOR
11 - OIL PRESSURE GAUGE 25 - FUEL GAUGE
12 - SKIS INDICATOR 26 - FRONT FOG LAMP INDICATOR
13 - MALFUNCTION INDICATOR LAMP (MIL) 27 - LOW FUEL INDICATOR
14 - CRUISE INDICATOR 28 - COOLANT LOW INDICATOR
8J - 4 INSTRUMENT CLUSTERWJ
INSTRUMENT CLUSTER (Continued)

The VFD is diagnosed using the EMIC self-diag-
nostic actuator test. (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND
TESTING). Proper testing of the PCI data bus and
the data bus message inputs to the EMIC that con-
trol the VFD functions requires the use of a DRBIIIt
scan tool. Refer to the appropriate diagnostic infor-
mation. Specific operation details for the odometer
and trip odometer functions of the VFD may be found
elsewhere in this service information.
INDICATORS
Indicators are located in various positions within
the EMIC and are all connected to the EMIC circuit
board. The turn signal indicators are hard wired. The
brake indicator is controlled by PCI data bus mes-
sages from the Controller Antilock Brake (CAB) as
well as by hard wired park brake switch and brake
fluid level switch inputs to the EMIC. The Malfunc-
tion Indicator Lamp (MIL) is normally controlled by
PCI data bus messages from the Powertrain Control
Module (PCM); however, if the EMIC loses PCI data
bus communication, the EMIC circuitry will automat-
ically turn the MIL on until PCI data bus communi-
cation is restored. The EMIC uses PCI data bus
messages from the Airbag Control Module (ACM), the
BCM, the PCM, the CAB, the Sentry Key Immobi-
lizer Module (SKIM), and the Transmission Control
Module (TCM) to control all of the remaining indica-
tors.
The various indicators are controlled by different
strategies; some receive fused ignition switch output
from the EMIC circuitry and have a switched ground,
others are grounded through the EMIC circuitry and
have a switched battery feed, while still others are
completely controlled by the EMIC microprocessor
based upon various hard wired and electronic mes-
sage inputs. Some indicators are illuminated at a
fixed intensity, while the illumination intensity of
others is synchronized with that of the EMIC general
illumination lamps.
The hard wired indicators are diagnosed using con-
ventional diagnostic methods. The EMIC and PCI
bus message controlled indicators are diagnosed
using the EMIC self-diagnostic actuator test. (Refer
to 8 - ELECTRICAL/INSTRUMENT CLUSTER -
DIAGNOSIS AND TESTING). Proper testing of the
PCI data bus and the electronic data bus message
inputs to the EMIC that control each indicator
require the use of a DRBIIItscan tool. Refer to the
appropriate diagnostic information. Specific details of
the operation for each indicator may be found else-
where in this service information.CLUSTER ILLUMINATION
Two types of general cluster illumination are avail-
able in this model. Base versions of the EMIC have
several incandescent illumination lamps, while pre-
mium versions of the EMIC have a single electro-lu-
minescent lamp. Both types of lamps provide cluster
back lighting whenever the exterior lighting is
turned On with the control knob on the left (lighting)
multi-function switch control stalk. The illumination
intensity of these lamps is adjusted by the EMIC
microprocessor based upon electronic dimming level
messages received from the Body Control Module
(BCM) over the PCI data bus. The BCM provides
electronic dimming level messages to the EMIC
based upon internal programming and inputs it
receives when the control ring on the left (lighting)
multi-function switch control stalk is rotated (down
to dim, up to brighten) to one of six available minor
detent positions.
The incandescent illumination lamps receive bat-
tery current at all times, while the ground for these
lamps is controlled by a 12-volt Pulse Width Modu-
lated (PWM) output of the EMIC electronic circuitry.
The illumination intensity of these bulbs and of the
vacuum-fluorescent electronic display are controlled
by the instrument cluster microprocessor based upon
dimming level messages received from the Body Con-
trol Module (BCM) over the PCI data bus. The BCM
uses inputs from the headlamp and panel dimmer
switches within the left (lighting) multi-function
switch control stalk and internal programming to
decide what dimming level message is required. The
BCM then sends the proper dimming level messages
to the EMIC over the PCI data bus.
The electro-luminescent lamp unit consists of lay-
ers of phosphor, carbon, idium tin oxide, and dielec-
tric applied by a silk-screen process between two
polyester membranes and includes a short pigtail
wire and connector. The lamp pigtail wire is con-
nected to a small connector receptacle on the EMIC
circuit board through a small clearance hole in the
cluster housing rear cover. The EMIC electronic cir-
cuitry also uses a PWM strategy to control the illu-
mination intensity of this lamp; however, the EMIC
powers this lamp with an Alternating Current (AC)
rated at 80 volts rms (root mean squared) and 415
Hertz, which excites the phosphor particles causing
them to luminesce.
The BCM also has several hard wired panel lamp
driver outputs and sends the proper panel lamps
dimming level messages over the PCI data bus to
coordinate the illumination intensity of all of the
instrument panel lighting and the VFDs of other
electronic modules on the PCI data bus. Vehicles
equipped with the Auto Headlamps option have an
automatic parade mode. In this mode, the BCM uses
8J - 6 INSTRUMENT CLUSTERWJ
INSTRUMENT CLUSTER (Continued)

pletely controlled by the instrument cluster logic cir-
cuit, and that logic will only allow this indicator to
operate when the instrument cluster receives a bat-
tery current input on the fused ignition switch out-
put (run-start) circuit. Therefore, the indicator will
always be off when the ignition switch is in any posi-
tion except On or Start. The bulb only illuminates
when it is provided a path to ground by the instru-
ment cluster transistor. The instrument cluster will
turn on the overdrive off indicator for the following
reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position the overdrive off indicator
is illuminated for about three seconds as a bulb test.
²Overdrive Off Indicator Lamp-On Message-
Each time the cluster receives an overdrive off indi-
cator lamp-on message from the PCM or TCM indi-
cating that the Off position of the overdrive off
switch has been selected, the overdrive off indicator
will be illuminated. The indicator remains illumi-
nated until the cluster receives an overdrive off indi-
cator lamp-off message from the PCM or TCM, or
until the ignition switch is turned to the Off position,
whichever occurs first.
²Actuator Test- Each time the cluster is put
through the actuator test, the overdrive off indicator
will be turned on for the duration of the test to con-
firm the functionality of the bulb and the cluster con-
trol circuitry.
The PCM or TCM continually monitors the over-
drive off switch to determine the proper outputs to
the automatic transmission. The PCM or TCM then
sends the proper overdrive off indicator lamp-on or
lamp-off messages to the instrument cluster. If the
overdrive off indicator fails to light during the bulb
test, replace the bulb with a known good unit. For
further diagnosis of the overdrive off indicator or the
instrument cluster circuitry that controls the indica-
tor, (Refer to 8 - ELECTRICAL/INSTRUMENT
CLUSTER - DIAGNOSIS AND TESTING). For
proper diagnosis of the overdrive control system, the
PCM, the TCM, the PCI data bus, or the electronic
message inputs to the instrument cluster that control
the overdrive off indicator, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
REAR FOG LAMP INDICATOR
DESCRIPTION
A rear fog lamp indicator is standard equipment on
all instrument clusters, but is only functional on
vehicles equipped with optional rear fog lamps,
which are available only in certain international
markets where they are required. The rear fog lampindicator is located on the left edge of the instrument
cluster, to the left of the tachometer. The rear fog
lamp indicator consists of an International Control
and Display Symbol icon for ªRear Fog Lightº
imprinted on an amber lens. The lens is located
behind a cutout in the opaque layer of the instru-
ment cluster overlay. The dark outer layer of the
overlay prevents the indicator from being clearly vis-
ible when it is not illuminated. The icon appears sil-
houetted against an amber field through the
translucent outer layer of the overlay when the indi-
cator is illuminated from behind by a replaceable
incandescent bulb and bulb holder unit located on
the instrument cluster electronic circuit board. When
the exterior lighting is turned On, the illumination
intensity of the rear fog lamp indicator is dimmable,
which is adjusted using the panel lamps dimmer con-
trol ring on the control stalk of the left multi-func-
tion switch. The rear fog lamp indicator lens is
serviced as a unit with the instrument cluster lens,
hood and mask unit.
OPERATION
The rear fog lamp indicator gives an indication to
the vehicle operator whenever the rear fog lamps are
illuminated. This indicator is controlled by a transis-
tor on the instrument cluster electronic circuit board
based upon cluster programming and electronic mes-
sages received by the cluster from the Body Control
Module (BCM) over the Programmable Communica-
tions Interface (PCI) data bus. The rear fog lamp
indicator bulb is completely controlled by the instru-
ment cluster logic circuit, and that logic will allow
this indicator to operate whenever the instrument
cluster receives a battery current input on the fused
B(+) circuit. Therefore, the indicator can be illumi-
nated regardless of the ignition switch position. The
bulb only illuminates when it is provided a path to
ground by the instrument cluster transistor. The
instrument cluster will turn on the rear fog lamp
indicator for the following reasons:
²Rear Fog Lamp Indicator Lamp-On Mes-
sage- Each time the cluster receives a rear fog lamp
indicator lamp-on message from the BCM indicating
that the rear fog lamps are turned On, the rear fog
lamp indicator will be illuminated. The indicator
remains illuminated until the cluster receives a rear
fog lamp indicator lamp-off message from the BCM.
²Actuator Test- Each time the cluster is put
through the actuator test, the rear fog lamp indicator
will be turned on for the duration of the test to con-
firm the functionality of the bulb and the cluster con-
trol circuitry.
The BCM continually monitors the exterior light-
ing (left multi-function) switch to determine the
proper outputs to the rear fog lamp relay. The BCM
WJINSTRUMENT CLUSTER 8J - 27
OVERDRIVE OFF INDICATOR (Continued)