2002 JEEP GRAND CHEROKEE pci bus

Control Module (PCM) over the Programmable Com-
munications Interface (PCI) data bus. The tachome-
ter is an air core magnetic unit that receives battery
current on the instrument cluster electronic circuit
board through the fused ignition switch output (run-
start) circuit whenever the ignition switch is in the
On or Start positions. The cluster is programmed to
move the gauge needle back to the low end of the
scale after the ignition switch is turned to the Off
position. The instrument cluster circuitry controls
the gauge needle position and provides the following
features:
²Engine Speed Message- Each time the cluster
receives an engine speed message from the PCM it
will calculate the correct engine speed reading and
position the gauge needle at that speed position on
the gauge scale. The cluster will receive a new
engine speed message and reposition the gauge
pointer accordingly about every 86 milliseconds. The
gauge needle will continue to be positioned at the
actual engine speed position on the gauge scale until
the ignition switch is turned to the Off position.
²Communication Error- If the cluster fails to
receive an engine speed message, it will hold the
gauge needle at the last indication for about six sec-
onds, or until the ignition switch is turned to the Off
position, whichever occurs first. If a new engine
speed message is not received after about six sec-
onds, the gauge needle will return to the far left
(low) end of the scale.
²Actuator Test- Each time the cluster is put
through the actuator test, the gauge needle will be
swept across the entire gauge scale and back in order
to confirm the functionality of the gauge and the
cluster control circuitry.
The PCM continually monitors the crankshaft posi-
tion sensor to determine the engine speed, then
sends the proper engine speed messages to the
instrument cluster. For further diagnosis of the
tachometer or the instrument cluster circuitry that
controls the gauge, (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND TEST-
ING). For proper diagnosis of the crankshaft position
sensor, the PCM, the PCI data bus, or the electronic
message inputs to the instrument cluster that control
the tachometer, a DRBIIItscan tool is required.
Refer to the appropriate diagnostic information.
TRANS TEMP INDICATOR
DESCRIPTION
A transmission over-temperature indicator is stan-
dard equipment on all gasoline engine instrument
clusters. The transmission over-temperature indica-
tor is located near the lower right corner of theinstrument cluster, to the right of the speedometer.
The transmission over-temperature indicator consists
of the words ªTRANS OVER TEMPº imprinted on an
amber lens. The lens is located behind a cutout in
the opaque layer of the instrument cluster overlay.
The dark outer layer of the overlay prevents the indi-
cator from being clearly visible when it is not illumi-
nated. The words ªTRANS OVER TEMPº appear
silhouetted against an amber field through the trans-
lucent outer layer of the overlay when the indicator
is illuminated from behind by a replaceable incandes-
cent bulb and bulb holder unit located on the instru-
ment cluster electronic circuit board. The
transmission over-temperature indicator lens is ser-
viced as a unit with the instrument cluster lens, hood
and mask unit.
OPERATION
The transmission over-temperature indicator gives
an indication to the vehicle operator when the trans-
mission fluid temperature is excessive, which may
lead to accelerated transmission component wear or
failure. This indicator is controlled by a transistor on
the instrument cluster electronic circuit board based
upon cluster programming and electronic messages
received by the cluster over the Programmable Com-
munications Interface (PCI) data bus. These mes-
sages are sent by the Powertrain Control Module
(PCM) or by the Transmission Control Module
(TCM), depending on the model of the automatic
transmission. The transmission over-temperature
indicator bulb is completely controlled by the instru-
ment cluster logic circuit, and that logic will only
allow this indicator to operate when the instrument
cluster receives a battery current input on the fused
ignition switch output (run-start) circuit. Therefore,
the indicator will always be off when the ignition
switch is in any position except On or Start. The bulb
only illuminates when it is provided a path to ground
by the instrument cluster transistor. The instrument
cluster will turn on the transmission over-tempera-
ture indicator for the following reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position the transmission over-tem-
perature indicator is illuminated for about three sec-
onds as a bulb test.
²Trans Over-Temp Indicator Lamp-On Mes-
sage- Each time the cluster receives a trans over-
temp indicator lamp-on message from the PCM or
TCM indicating that the transmission fluid tempera-
ture is 135É C (275É F) or higher, the transmission
over-temperature indicator will be illuminated. The
indicator remains illuminated until the cluster
receives a trans over-temp indicator lamp-off mes-
sage from the PCM or TCM, or until the ignition
8J - 32 INSTRUMENT CLUSTERWJ
TACHOMETER (Continued)

switch is turned to the Off position, whichever occurs
first.
²Actuator Test- Each time the cluster is put
through the actuator test, the transmission over-tem-
perature indicator will be turned on for the duration
of the test to confirm the functionality of the bulb
and the cluster control circuitry.
The PCM or TCM continually monitors the trans-
mission temperature sensor to determine the trans-
mission operating condition. The PCM or TCM then
sends the proper trans over-temp indicator lamp-on
or lamp-off messages to the instrument cluster. If the
transmission over-temperature indicator fails to light
during the bulb test, replace the bulb with a known
good unit. If the instrument cluster turns on the
transmission over-temperature indicator due to a
high transmission oil temperature condition, it may
indicate that the transmission or the transmission
cooling system are being overloaded or that they
require service. For further diagnosis of the trans-
mission over-temperature indicator or the instrument
cluster circuitry that controls the indicator, (Refer to
8 - ELECTRICAL/INSTRUMENT CLUSTER - DIAG-
NOSIS AND TESTING). For proper diagnosis of the
transmission temperature sensor, the PCM, the
TCM, the PCI data bus, or the electronic message
inputs to the instrument cluster that control the
transmission over-temperature indicator, a DRBIIIt
scan tool is required. Refer to the appropriate diag-
nostic information.
TURN SIGNAL INDICATOR
DESCRIPTION
Two turn signal indicators, one right and one left,
are standard equipment on all instrument clusters.
The turn signal indicators are located near the upper
edge of the instrument cluster, the left one is left of
the tachometer, and the right one is right of the
speedometer. Each turn signal indicator consists of
an International Control and Display Symbol icon for
ªTurn Warningº imprinted on a green lens. Each lens
is located behind a dedicated cutout in the opaque
layer of the instrument cluster overlay. The dark
outer layer of the overlay prevents these icons from
being clearly visible when they are not illuminated.
The icons appear silhouetted against a green field
through the translucent outer layer of the overlay
when the indicator is illuminated from behind by a
replaceable incandescent bulb and bulb holder unit
located on the instrument cluster electronic circuit
board. The turn signal indicator lenses are serviced
as a unit with the instrument cluster lens, hood and
mask unit.
OPERATION
The turn signal indicators give an indication to the
vehicle operator that the turn signal (left or right
indicator flashing) or hazard warning (both left and
right indicators flashing) have been selected and are
operating. These indicators are controlled by two
individual hard wired inputs from the combination
flasher circuitry to the instrument cluster electronic
circuit board. Each turn signal indicator bulb is
grounded on the instrument cluster electronic circuit
board at all times; therefore, these indicators remain
functional regardless of the ignition switch position.
Each indicator bulb will only illuminate when it is
provided with battery current by the combination
flasher in the Junction Block (JB).
The turn signal indicators are connected in parallel
with the other turn signal circuits. This arrangement
allows the turn signal indicators to remain func-
tional, regardless of the condition of the other cir-
cuits in the turn signal and hazard warning systems.
The combination flasher outputs to the instrument
cluster turn signal indicator inputs can be diagnosed
using conventional diagnostic tools and methods. For
more information on the turn signal and hazard
warning system, (Refer to 8 - ELECTRICAL/LAMPS/
LIGHTING - EXTERIOR - OPERATION - TURN
SIGNAL & HAZARD WARNING SYSTEM).
DIAGNOSIS AND TESTING - TURN SIGNAL
INDICATOR
The diagnosis found here addresses an inoperative
turn signal indicator condition. If the problem being
diagnosed is related to inoperative turn signal or
hazard warning lamps, be certain to repair the turn
signal and hazard warning system before attempting
to diagnose or repair the turn signal indicators.
(Refer to 8 - ELECTRICAL/LAMPS/LIGHTING -
EXTERIOR - DIAGNOSIS AND TESTING - TURN
SIGNAL & HAZARD WARNING SYSTEM). If no
turn signal and hazard warning system problem is
found, the following procedure will help locate an
open in the turn signal indicator circuit. Refer to the
appropriate wiring information. The wiring informa-
tion includes wiring diagrams, proper wire and con-
nector repair procedures, details of wire harness
routing and retention, connector pin-out information
and location views for the various wire harness con-
nectors, splices and grounds.
WJINSTRUMENT CLUSTER 8J - 33
TRANS TEMP INDICATOR (Continued)

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,
PASSENGER AIRBAG, SIDE CURTAIN AIRBAG,
FRONT IMPACT SENSOR, SIDE IMPACT SENSOR,
OR INSTRUMENT PANEL COMPONENT DIAGNOSIS
OR SERVICE. DISCONNECT AND ISOLATE THE
BATTERY NEGATIVE (GROUND) CABLE, THEN
WAIT TWO MINUTES FOR THE SYSTEM CAPACI-
TOR TO DISCHARGE BEFORE PERFORMING FUR-
THER DIAGNOSIS OR SERVICE. THIS IS THE ONLY
SURE WAY TO DISABLE THE SUPPLEMENTAL
RESTRAINT SYSTEM. FAILURE TO TAKE THE
PROPER PRECAUTIONS COULD RESULT IN ACCI-
DENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.
(1) Disconnect and isolate the battery negative
cable. Remove the instrument cluster from the
instrument panel and disconnect the instrument
panel wire harness for the instrument cluster from
the cluster connector receptacle.
(2) Reconnect the battery negative cable. Activate
the hazard warning system by moving the hazard
warning switch button to the On position. Check for
battery voltage at the inoperative (right or left) turn
signal circuit cavity of the instrument panel wire
harness connector for the instrument cluster. There
should be a switching (on and off) battery voltage sig-
nal present. If OK, replace the faulty (right or left)
turn signal indicator bulb. If not OK, repair the open
(right or left) turn signal circuit between the instru-
ment cluster and the combination flasher in the
Junction Block (JB) as required.
VOLTAGE GAUGE
DESCRIPTION
A voltage gauge is standard equipment on all
instrument clusters. The voltage gauge is located in
the upper left corner of the instrument cluster, to the
left of the tachometer. The voltage gauge consists of a
movable gauge needle or pointer controlled by the
instrument cluster circuitry and a fixed 90 degree
scale on the gauge dial face that reads left-to-right
from 9 volts to 19 volts. An International Control and
Display Symbol icon for ªBattery Charging Condi-
tionº is located on the gauge dial face.
The voltage gauge graphics are either white, gray
and orange against a black gauge dial face (base
cluster) or black, gray and red against a taupe gauge
dial face (premium cluster), making them clearly vis-
ible within the instrument cluster in daylight. When
illuminated from behind by the panel lamps dimmer
controlled cluster illumination lighting with the exte-rior lamps turned On, the base cluster white gauge
graphics appear blue-green and the orange graphics
still appear orange, while the premium cluster taupe
gauge dial face appears blue-green with the black
graphics silhouetted against the illuminated back-
ground and the red graphics still appear red. The
gray gauge graphics for both versions of the cluster
are not illuminated. The orange gauge needle in the
base cluster gauge is internally illuminated, while
the black gauge needle in the premium cluster gauge
is not.
Base cluster gauge illumination is provided by
replaceable incandescent bulb and bulb holder units
located on the instrument cluster electronic circuit
board. Premium cluster gauge illumination is pro-
vided by an integral electro-luminescent lamp that is
serviced as a unit with the instrument cluster. The
voltage gauge is serviced as a unit with the instru-
ment cluster.
OPERATION
The voltage gauge gives an indication to the vehi-
cle operator of the electrical system voltage. This
gauge is controlled by the instrument cluster circuit
board based upon cluster programming and elec-
tronic messages received by the cluster from the
Powertrain Control Module (PCM) over the Program-
mable Communications Interface (PCI) data bus. The
voltage gauge is an air core magnetic unit that
receives battery current on the instrument cluster
electronic circuit board through the fused ignition
switch output (run-start) circuit whenever the igni-
tion switch is in the On or Start positions. The clus-
ter is programmed to move the gauge needle back to
the low end of the scale after the ignition switch is
turned to the Off position. The instrument cluster
circuitry controls the gauge needle position and pro-
vides the following features:
²System Voltage Message- Each time the clus-
ter receives a message from the PCM indicating the
system voltage, the cluster moves the gauge needle to
the relative voltage level position on the gauge scale.
²System Voltage Low Message- Each time the
cluster receives a message from the PCM indicating
the system voltage is low (system voltage is about
eleven volts or lower), the gauge needle is moved to
the relative voltage position in the red zone of the
gauge scale and the check gauges indicator is illumi-
nated. The gauge needle remains in the red zone and
the check gauges indicator remains illuminated until
the cluster receives a message from the PCM indicat-
ing there is no low system voltage condition (system
voltage is above about eleven volts, but lower than
about sixteen volts).
²System Voltage High Message- Each time
the cluster receives a message from the PCM indicat-
8J - 34 INSTRUMENT CLUSTERWJ
TURN SIGNAL INDICATOR (Continued)

ing the system voltage is high (system voltage is
about sixteen volts or higher), the gauge needle is
moved to the relative voltage position in the red zone
of the gauge scale and the check gauges indicator is
illuminated. The gauge needle remains in the red
zone and the check gauges indicator remains illumi-
nated until the cluster receives a message from the
PCM indicating there is no high system voltage con-
dition (system voltage is below about sixteen volts,
but higher than about eleven volts).
²Communication Error- If the cluster fails to
receive a system voltage message, it will hold the
gauge needle at the last indication for about twelve
seconds, until a new message is received, or until the
ignition switch is turned to the Off position, which-
ever occurs first. After twelve seconds, the cluster
will return the gauge needle to the low end of the
gauge scale.
²Actuator Test- Each time the cluster is put
through the actuator test, the gauge needle will be
swept across the entire gauge scale and back to con-
firm the functionality of the gauge and the cluster
control circuitry.
The PCM continually monitors the system voltage
to control the generator output. The PCM then sends
the proper system voltage messages to the instru-
ment cluster. For further diagnosis of the voltage
gauge or the instrument cluster circuitry that con-
trols the gauge, (Refer to 8 - ELECTRICAL/INSTRU-
MENT CLUSTER - DIAGNOSIS AND TESTING). If
the instrument cluster turns on the check gauges
indicator due to a system voltage low or high condi-
tion, it may indicate that the charging system
requires service. For proper diagnosis of the charging
system, the PCI data bus, or the electronic message
inputs to the instrument cluster that control the volt-
age gauge, a DRBIIItscan tool is required. Refer to
the appropriate diagnostic information.
WAIT-TO-START INDICATOR
DESCRIPTION
A wait-to-start indicator is only found in the
instrument clusters of vehicles equipped with an
optional diesel engine. The wait-to-start indicator is
located near the lower edge of the tachometer gauge
dial face, to the right of center. The wait-to-start
indicator consists of an International Control and
Display Symbol icon for ªDiesel Preheatº imprinted
on an amber lens. The lens is located behind a cutout
in the opaque layer of the tachometer gauge dial face
overlay. The dark outer layer of the gauge dial face
overlay prevents the icon from being clearly visible
when the indicator is not illuminated. The icon
appears silhouetted against an amber field throughthe translucent outer layer of the gauge dial face
overlay when the indicator is illuminated from
behind by a replaceable incandescent bulb and bulb
holder unit located on the instrument cluster elec-
tronic circuit board. The wait-to-start indicator lens
is serviced as a unit with the instrument cluster.
OPERATION
The wait-to-start indicator gives an indication to
the vehicle operator when the diesel engine glow
plugs are energized in their preheat operating mode.
This indicator is controlled by a transistor on the
instrument cluster circuit board based upon cluster
programming and electronic messages received by
the cluster from the Powertrain Control Module
(PCM) over the Programmable Communications
Interface (PCI) data bus. The wait-to-start indicator
bulb is completely controlled by the instrument clus-
ter logic circuit, and that logic will only allow this
indicator to operate when the instrument cluster
receives a battery current input on the fused ignition
switch output (run-start) circuit. Therefore, the indi-
cator will always be off when the ignition switch is in
any position except On or Start. The bulb only illu-
minates when it is switched to ground by the instru-
ment cluster transistor. The instrument cluster will
turn on the wait-to-start indicator for the following
reasons:
²Wait-To-Start Indicator Lamp-On Message-
Each time the cluster receives a wait-to-start indica-
tor lamp-on message from the PCM indicating the
glow plugs are heating and the driver must wait to
start the engine, the wait-to-start indicator will be
illuminated. The indicator remains illuminated until
the cluster receives a wait-to-start indicator lamp-off
message, 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 wait-to-start 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 continually monitors the ambient tem-
perature and the glow plug pre-heater circuits to
determine how long the glow plugs must be heated in
the pre-heat operating mode. The PCM then sends
the proper wait-to-start indicator lamp-on and lamp-
off messages to the instrument cluster. If the wait-to-
start indicator fails to light during the actuator test,
replace the bulb with a known good unit. For further
diagnosis of the wait-to-start indicator or the instru-
ment cluster circuitry that controls the indicator,
(Refer to 8 - ELECTRICAL/INSTRUMENT CLUS-
TER - DIAGNOSIS AND TESTING). For proper
diagnosis of the glow plug pre-heater control circuits,
the PCM, the PCI data bus, or the electronic message
WJINSTRUMENT CLUSTER 8J - 35
VOLTAGE GAUGE (Continued)

inputs to the instrument cluster that control the
wait-to-start indicator, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
WATER-IN-FUEL INDICATOR
DESCRIPTION
A water-in-fuel indicator is only found in the
instrument clusters of vehicles equipped with an
optional diesel engine. The water-in-fuel indicator is
located near the left edge of the instrument cluster,
to the left of the tachometer. The water-in-fuel indi-
cator consists of an International Control and Dis-
play Symbol icon for ªWater in Fuelº imprinted on a
red lens. The lens is located behind a cutout in the
opaque layer of the instrument cluster overlay. The
dark outer layer of the overlay prevents the icon
from being clearly visible when the indicator is not
illuminated. The icon appears silhouetted against a
red field through the translucent outer layer of the
overlay when the indicator is illuminated from
behind by a Light Emitting Diode (LED), which is
soldered onto the instrument cluster electronic circuit
board. The water-in-fuel indicator lens is serviced as
a unit with the instrument cluster lens, hood and
mask unit.
OPERATION
The water-in-fuel indicator gives an indication to
the vehicle operator when there is excessive water in
the fuel system. This indicator is controlled by a
transistor on the instrument cluster circuit board
based upon cluster programming and electronic mes-
sages received by the cluster from the Powertrain
Control Module (PCM) over the Programmable Com-
munications Interface (PCI) data bus. The water-in-
fuel indicator Light Emitting Diode (LED) is
completely controlled by the instrument cluster logic
circuit, and that logic will only allow this indicator tooperate 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 LED only illuminates
when it is provided a path to ground by the instru-
ment cluster transistor. The instrument cluster will
turn on the water-in-fuel indicator for the following
reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position the water-in-fuel indicator
is illuminated for about three seconds as a bulb test.
²Water-In-Fuel Indicator Lamp-On Message-
Each time the cluster receives a water-in-fuel indica-
tor lamp-on message from the PCM indicating there
is excessive water in the diesel fuel system, the
water-in-fuel indicator will be illuminated. The indi-
cator remains illuminated until the cluster receives a
water-in-fuel indicator lamp-off message, or until the
ignition switch is turned to the Off position, which-
ever occurs first.
²Actuator Test- Each time the cluster is put
through the actuator test, the water-in-fuel indicator
will be turned on for the duration of the test to con-
firm the functionality of the LED and the cluster con-
trol circuitry.
The PCM continually monitors the water-in-fuel
sensor to determine whether there is excessive water
in the diesel fuel. The PCM then sends the proper
water-in-fuel indicator lamp-on and lamp-off mes-
sages to the instrument cluster. For further diagnosis
of the water-in-fuel indicator or the instrument clus-
ter circuitry that controls the indicator, (Refer to 8 -
ELECTRICAL/INSTRUMENT CLUSTER - DIAGNO-
SIS AND TESTING). For proper diagnosis of the
water-in-fuel sensor, the PCM, the PCI data bus, or
the electronic message inputs to the instrument clus-
ter that control the water-in-fuel indicator, a
DRBIIItscan tool is required. Refer to the appropri-
ate diagnostic information.
8J - 36 INSTRUMENT CLUSTERWJ
WAIT-TO-START INDICATOR (Continued)

ergize the combination flasher in response to mes-
sage inputs received over the Programmable
Communications Interface (PCI) data bus network.
The BCM can energize the combination flasher when
the VTSS is requested.
Vehicles equipped with the optional Electronic
Vehicle Information Center (EVIC) use turn signal
status messages received from the Electro-Mechani-
cal Instrument Cluster (EMIC) and distance mes-
sages received from the Powertrain Control Module
(PCM) over the PCI data bus to determine when the
Turn Signal On warning should be activated. The
EMIC receives hard wired inputs from the combina-
tion flasher to operate the turn signal indicators,
then sends the proper turn signal status message to
the EVIC. If a turn signal is left on for more than
about 1.6 kilometers (1 mile) of driving distance, the
EVIC will display a visual ªTurn Signal Onº message
and will send a request to the BCM over the PCI
data bus to notify the vehicle operator.
During both the turn signal and the hazard warn-
ing operation, if the exterior lamps are turned Off,
the front park/turn signal lamps and the front side
marker lamps will flash in unison. If the exterior
lamps are turned On, the front park/turn signal
lamps and the front side marker lamps will flash
alternately. Refer to the owner's manual.
DIAGNOSIS AND TESTING - TURN SIGNAL &
HAZARD WARNING SYSTEMS
When diagnosing the turn signal and hazard warn-
ing circuits, remember that high generator output
can burn out bulbs rapidly and repeatedly. If this is a
concern on the vehicle being diagnosed, test the
charging system as required.
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 ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Turn the ignition switch to the On position.
Actuate the turn signal switch or the hazard warning
switch. Observe the turn signal indicator lamp(s) in
the instrument cluster. If the flash rate is very high,
check for a turn signal bulb that is not lit or is verydimly lit. Repair the circuits to that lamp or replace
the faulty bulb, as required. If the turn signal indi-
cator(s) fail to light, go to Step 2.
(2) Turn the ignition switch to the Off position.
Check the ignition run fuse and the flasher fuse in
the Junction Block (JB). If OK, go to Step 3. If not
OK, repair the shorted circuit or component as
required and replace the faulty fuse(s).
(3) Check for battery voltage at the flasher fuse in
the JB. If OK, go to Step 4. If not OK, repair the
open fused B(+) circuit between the JB and the
Power Distribution Center (PDC).
(4) Turn the ignition switch to the On position.
Check for battery voltage at the ignition run fuse in
the JB. If OK, go to Step 5. If not OK, repair the
open fused ignition switch output (run) circuit
between the JB and the ignition switch.
(5) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Remove the combination flasher from the JB and
replace it with a known good unit. Reconnect the bat-
tery negative cable. Test the operation of the turn
signal and hazard warning systems. If OK, discard
the faulty combination flasher. If not OK, remove the
test flasher and go to Step 6.
(6) Turn the ignition switch to the On position.
Check for battery voltage at the fused ignition switch
output (run) circuit cavity in the JB for the combina-
tion flasher. If OK, go to Step 7. If not OK, repair the
open fused ignition switch output (run) circuit
between the combination flasher and the ignition run
fuse in the JB.
(7) Turn the ignition switch to the Off position.
Check for battery voltage at the B(+) circuit of the JB
for the combination flasher. If OK, go to Step 8. If
not OK, repair the open B(+) circuit between the
combination flasher and the flasher fuse in the JB.
(8) Disconnect and isolate the battery negative
cable. Disconnect the instrument panel wire harness
connector for the turn signal and hazard warning
switches from the multi-function switch connector.
Check for continuity between the ground circuit of
the instrument panel wire harness connector for the
left multi-function switch and a good ground. There
should be continuity. If OK, go to Step 9. If not OK,
repair the open ground circuit.
(9) Check for continuity between the hazard switch
sense circuit of the instrument panel wire harness
connector for the multi-function switch and a good
ground. There should be no continuity. If OK, go to
Step 10. If not OK, repair the shorted hazard switch
sense circuit between the multi-function switch and
the combination flasher.
(10) Check for continuity between the hazard
switch sense circuit of the JB for the combination
flasher and the instrument panel wire harness con-
WJLAMPS/LIGHTING - EXTERIOR 8L - 3
LAMPS/LIGHTING - EXTERIOR (Continued)

INSTALLATION - BULB
CAUTION: Do not touch the bulb glass with fingers
or other oily surfaces. Reduced bulb life will result.
(1) Position the bulb into socket and push into
place.
(2) Position the bulb socket in headlamp and turn
the bulb socket one quarter turn clockwise.
(3) Install the headlamp.
HEADLAMP SWITCH
DESCRIPTION
The headlamp switch is part of the left multi-func-
tion switch. A knob on the end of the multi-function
switch control stalk controls all of the exterior light-
ing switch functions. The exterior lighting switch is
hard wired to the Body Control Module (BCM).
The exterior lighting switch cannot be adjusted or
repaired and, if faulty or damaged, the entire left
multi-function switch unit must be replaced. (Refer
to 8 - ELECTRICAL/LAMPS/LIGHTING - EXTERI-
OR/TURN SIGNAL/HAZARD SWITCH - REMOVAL)
for the service procedures. (Refer to 8 - ELECTRI-
CAL/ELECTRONIC CONTROL MODULES/BODY
CONTROL/CENTRAL TIMER MODUL - DESCRIP-
TION) for more information on this component.
OPERATION
The exterior lighting switch uses a hard wired five
volt reference circuit from the BCM, resistor multi-
plexing and a hard wired switch output circuit to
provide the BCM with a zero to five volt signal thatindicates the status of all of the exterior lighting
switch settings. The BCM then uses control outputs
to energize the headlamp and park lamp relays that
activate the exterior lighting circuits.
The BCM monitors the exterior lighting switch sta-
tus, then sends the proper switch status messages to
other modules over the Programmable Communica-
tions Interface (PCI) data bus network. The exterior
lighting switch status is also used by the BCM as an
input for chime warning system operation.
DIAGNOSIS AND TESTING Ð HEADLAMP
SWITCH
Before testing the headlamp switch, turn on the
exterior lighting and open the driver side front door.
If the exterior lamps of the vehicle operate, but there
is no chime warning issued with the driver side front
door open, (Refer to 8 - ELECTRICAL/LAMPS/
LIGHTING - INTERIOR/DOOR AJAR SWITCH -
DIAGNOSIS AND TESTING). If the exterior lamps
of the vehicle are inoperative, but the chime warning
is issued, (Refer to 8 - ELECTRICAL/LAMPS/LIGHT-
ING - EXTERIOR - DIAGNOSIS AND TESTING).
If the exterior lamps and the chime warning are
both inoperative, test the left multi-function switch.
(Refer to 8 - ELECTRICAL/LAMPS/LIGHTING -
EXTERIOR - DIAGNOSIS AND TESTING). If the
multi-function switch tests OK, proceed as follows.
The following tests will help to locate a short or open
in the hard wired circuits between the multi-function
switch and the Body Control Module (BCM). For
complete circuit diagrams, refer to the appropriate
wiring information.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO ELECTRICAL, RESTRAINTS
BEFORE ATTEMPTING ANY STEERING WHEEL,
STEERING COLUMN, OR INSTRUMENT PANEL
COMPONENT DIAGNOSIS OR SERVICE. FAILURE
TO TAKE THE PROPER PRECAUTIONS COULD
RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT
AND POSSIBLE PERSONAL INJURY.
(1) Disconnect and isolate the battery negative
cable. Disconnect the instrument panel wire harness
connector from the left multi-function switch connec-
tor. Disconnect the instrument panel wire harness
connector from the Body Control Module (BCM).
Check for continuity between the headlamp switch
mux circuit of the instrument panel wire harness
connector for the multi-function switch and a good
ground. There should be no continuity. If OK, go to
Step 2. If not OK, repair the shorted headlamp
switch mux circuit.
(2) Check for continuity between the headlamp
switch mux circuit of the instrument panel wire har-
Fig. 13 Headlamp Bulb
1 - HIGH BEAM BULB
2 - LOW BEAM BULB
3 - MARKER BULB
4 - PARK/TURN SIGNAL BULB
WJLAMPS/LIGHTING - EXTERIOR 8L - 15
HEADLAMP (Continued)

²Hazard Warning Control- The hazard warn-
ing push button is pressed down to activate the haz-
ard warning system, and pressed down again to turn
the system off. The left multi-function switch pro-
vides a ground to the hazard warning sense input of
the combination flasher to control activation of the
hazard warning lamps.
²Headlamps- The Body Control Module (BCM)
monitors the left multi-function switch then, based
upon that multiplexed input, controls an output to
the headlamp low or high beam relays to illuminate
or extinguish the headlamps.
²Headlamp Beam Selection- The Body Control
Module (BCM) monitors the left multi-function
switch then, based upon that switched ground input,
controls an output to the headlamp low or high beam
relays to activate the selected headlamp beam.
²Headlamp Optical Horn- The Body Control
Module (BCM) monitors the left multi-function
switch then, based upon that switched ground input,
controls an output to the headlamp high beam relay
to activate the headlamp high beams.
²Park Lamps- The Body Control Module (BCM)
monitors the left multi-function switch then, based
upon that multiplexed input, controls an output to
the park lamp relay to illuminate or extinguish the
parking lamps.
²Rear Fog Lamps- The Body Control Module
(BCM) monitors the left multi-function switch then,
based upon that multiplexed input, controls an out-
put to the rear fog lamp relay to illuminate or extin-
guish the rear fog lamps.
²Turn Signal Control- The left multi-function
switch control stalk actuates the turn signal switch.
The Body Control Module (BCM) monitors the left
multi-function switch then, based upon that multi-
plexed input, provides a variable voltage output to
control the lighting of the turn signals.
Following are descriptions of the how the left
multi-function switch operates to control the many
interior lighting functions and features it provides:
²Panel Lamps Dimming- The Body Control
Module (BCM) monitors the left multi-function
switch then, based upon that multiplexed input, pro-
vides a variable voltage output through several panel
lamps driver circuits to control the lighting of many
incandescent panel lamps. The BCM also sends panel
lamps dimming messages over the Programmable
Communications Interface (PCI) data bus to other
modules to control Display lighting levels in those
modules.²Interior Lamps Defeat- The Body Control
Module (BCM) monitors the left multi-function
switch then, based upon that multiplexed input,
internally disables the function the BCM normally
provides to control the illumination of the interior
lamps.
²Interior Lamps On- The Body Control Module
(BCM) monitors the left multi-function switch then,
based upon that multiplexed input, provides a control
output to activate all of the interior lamp circuits.
²Parade Mode- The Body Control Module
(BCM) monitors the left multi-function switch then,
based upon that multiplexed input, provides a volt-
age output through several panel lamps driver cir-
cuits to control the lighting of many incandescent
panel lamps. The BCM also sends panel lamps dim-
ming messages over the Programmable Communica-
tions Interface (PCI) data bus to other modules on
the bus to control lighting levels in those modules.
DIAGNOSIS AND TESTING - LEFT MULTI -
FUNCTION SWITCH
Refer to the appropriate 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 ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable. Disconnect the instrument panel wire harness
connector from the multi-function switch connector.
(2) Using an ohmmeter, perform the continuity
and resistance tests at the terminals in the multi-
function switch connector as shown in the Left Multi-
Function Switch Test chart (Fig. 23).
8L - 20 LAMPS/LIGHTING - EXTERIORWJ
LEFT MULTI-FUNCTION SWITCH (Continued)