2003 DODGE RAM bulb

must be displaying the odometer information when
the trip odometer reset switch button is pressed in
order to toggle to the engine hours display. The
engine hours will remain displayed for about thirty
seconds, until the engine speed message is greater
than zero, or until the ignition switch is turned to
the Off position, whichever occurs first.
²Trip Odometer Reset- When the trip odome-
ter reset switch button is pressed and held for longer
than about two seconds with the ignition switch in
the On or Start positions, the trip odometer will be
reset to 0.0 kilometers (miles). The VFD must be dis-
playing the trip odometer information in order for
the trip odometer information to be reset.
²Communication Error- If the cluster fails to
receive a distance message during normal operation,
it will hold and display the last data received until
the ignition switch is turned to the Off position. If
the cluster does not receive a distance message
within one second after the ignition switch is turned
to the On position, it will display the last distance
message stored in the cluster memory. If the cluster
is unable to display distance information due to an
error internal to the cluster, the VFD display will be
dashes.
²Actuator Test- Each time the cluster is put
through the actuator test, the odometer VFD will dis-
play all of its segments simultaneously during the
VFD portion of the test to confirm the functionality
of each of the VFD segments and the cluster control
circuitry.
The PCM continually monitors the vehicle speed
pulse information received from the vehicle speed
sensor and engine speed pulse information received
from the crankshaft position sensor, then sends the
proper distance and engine speed messages to the
instrument cluster. For further diagnosis of the
odometer/trip odometer or the instrument cluster cir-
cuitry that controls these functions, (Refer to 8 -
ELECTRICAL/INSTRUMENT CLUSTER - DIAGNO-
SIS AND TESTING). For proper diagnosis of the
vehicle speed sensor, the crankshaft position sensor,
the PCM, the PCI data bus, or the electronic message
inputs to the instrument cluster that control the
odometer/trip odometer, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
OIL PRESSURE GAUGE
DESCRIPTION
An oil pressure gauge is standard equipment on all
instrument clusters. The oil pressure gauge is located
in the upper right quadrant of the instrument clus-
ter, above the coolant temperature gauge. The oilpressure gauge consists of a movable gauge needle or
pointer controlled by the instrument cluster circuitry
and a fixed 90 degree scale on the cluster overlay
that reads left-to-right from ªLº (or Low) to ªHº (or
High) for gasoline engines. On vehicles with a diesel
engine the scale reads from ª0º kPa to ª760º kPa in
markets where a metric instrument cluster is speci-
fied, or from ª0º psi to ª110º psi in all other markets.
An International Control and Display Symbol icon for
ªEngine Oilº is located on the cluster overlay, directly
below the left end of the gauge scale. The oil pres-
sure gauge graphics are black against a white field
except for two red graduations at the low end of the
gauge scale, making them clearly visible within the
instrument cluster in daylight. When illuminated
from behind by the panel lamps dimmer controlled
cluster illumination lighting with the exterior lamps
turned On, the black graphics appear blue and the
red graphics still appear red. The orange gauge nee-
dle is internally illuminated. Gauge illumination is
provided by replaceable incandescent bulb and bulb
holder units located on the instrument cluster elec-
tronic circuit board. The oil pressure gauge is ser-
viced as a unit with the instrument cluster.
OPERATION
The oil pressure gauge gives an indication to the
vehicle operator of the engine oil pressure. 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) on vehicles with a
gasoline engine, or from the Engine Control Module
(ECM) on vehicles equipped with a diesel engine over
the Programmable Communications Interface (PCI)
data bus. The oil pressure gauge is an air core mag-
netic unit that receives battery current on the instru-
ment cluster electronic circuit board through the
fused ignition switch output (run-start) circuit when-
ever the ignition switch is in the On or Start posi-
tions. The cluster is programmed to move the gauge
needle back to the low end of the scale after the igni-
tion switch is turned to the Off position. The instru-
ment cluster circuitry controls the gauge needle
position and provides the following features:
²Engine Oil Pressure Message- The instru-
ment cluster circuitry restricts the oil pressure gauge
needle operation in order to provide readings that
are consistent with customer expectations. Each time
the cluster receives a message from the PCM or ECM
indicating the engine oil pressure is above about 41
kPa (6 psi) the cluster holds the gauge needle at a
point near the middle increment within the normal
range on the gauge scale.
²Engine Oil Pressure Low Message- Each
time the cluster receives a message from the PCM or
8J - 32 INSTRUMENT CLUSTERDR
ODOMETER (Continued)

instrument cluster. For further diagnosis of the over-
drive off indicator or the instrument cluster circuitry
that controls the indicator, (Refer to 8 - ELECTRI-
CAL/INSTRUMENT CLUSTER - DIAGNOSIS AND
TESTING). For proper diagnosis of the overdrive con-
trol system, the PCM, the PCI data bus, or the elec-
tronic message inputs to the instrument cluster that
control the overdrive off indicator, a DRBIIItscan
tool is required. Refer to the appropriate diagnostic
information.
SEATBELT INDICATOR
DESCRIPTION
A seatbelt indicator is standard equipment on all
instrument clusters. The seatbelt indicator is located
on the upper edge of the instrument cluster, between
the tachometer and the speedometer. The seatbelt
indicator consists of a stencil-like cutout of the Inter-
national Control and Display Symbol icon for ªSeat
Beltº in the opaque layer of the instrument cluster
overlay. The dark outer layer of the overlay prevents
the indicator from being clearly visible when it is not
illuminated. A red Light Emitting Diode (LED)
behind the cutout in the opaque layer of the overlay
causes the icon to appear in red through the translu-
cent outer layer of the overlay when the indicator is
illuminated from behind by the LED, which is sol-
dered onto the instrument cluster electronic circuit
board. The seatbelt indicator is serviced as a unit
with the instrument cluster.
OPERATION
The seatbelt indicator gives an indication to the
vehicle operator of the status of the driver side front
seatbelt. This indicator is controlled by a transistor
on the instrument cluster circuit board based upon
cluster programming and a hard wired input from
the seatbelt switch in the driver side front seatbelt
buckle through the seat belt indicator driver circuit.
The seatbelt indicator Light Emitting Diode (LED) is
completely controlled by the instrument cluster logic
circuit, 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 LED 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 seatbelt indicator for the following rea-
sons:
²Seatbelt Reminder Function- Each time the
cluster receives a battery current input on the fused
ignition switch output (run-start) circuit, the indica-tor will be illuminated as a seatbelt reminder for
about six seconds, or until the ignition switch is
turned to the Off position, whichever occurs first.
This reminder function will occur regardless of the
status of the seatbelt switch input to the cluster.
²Driver Side Front Seatbelt Not Buckled-
Following the seatbelt reminder function, each time
the cluster detects an open circuit on the seat belt
indicator driver circuit (seatbelt switch open = seat-
belt unbuckled) with the ignition switch in the Start
or On positions, the indicator will be illuminated.
The seatbelt indicator remains illuminated until the
seat belt indicator driver input to the cluster is
closed to ground (seatbelt switch closed = seatbelt
buckled), or until the ignition switch is turned to the
Off position, whichever occurs first.
²Airbag Indicator Backup- If the instrument
cluster detects a fault in the airbag indicator circuit
it will send a message indicating the fault to the Air-
bag Control Module (ACM), store a Diagnostic Trou-
ble Code (DTC) in the cluster memory, then flash the
seatbelt indicator on and off. The cluster will con-
tinue to flash the seatbelt indicator until the airbag
indicator circuit fault is resolved, 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 seatbelt indicator will
be turned on, then off again during the bulb check
portion of the test to confirm the functionality of the
LED and the cluster control circuitry.
The seatbelt switch is connected in series between
ground and the seat belt indicator driver input to the
instrument cluster. The seatbelt switch input to the
instrument cluster circuitry may be diagnosed using
conventional diagnostic tools and methods. For fur-
ther diagnosis of the seatbelt indicator or the instru-
ment cluster circuitry that controls the LED, (Refer
to 8 - ELECTRICAL/INSTRUMENT CLUSTER -
DIAGNOSIS AND TESTING).
SECURITY INDICATOR
DESCRIPTION
A security indicator is standard equipment on all
instrument clusters. However, on vehicles not
equipped with the optional Vehicle Theft Security
System (VTSS), this indicator is electronically dis-
abled. The security indicator is located in the lower
right quadrant of the instrument cluster, between the
speedometer and the coolant temperature gauge. The
security indicator consists of a small round 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-
8J - 34 INSTRUMENT CLUSTERDR
OVERDRIVE OFF INDICATOR (Continued)

nated. A red Light Emitting Diode (LED) behind the
cutout in the opaque layer of the overlay causes the
indicator to appear in red through the translucent
outer layer of the overlay when it is illuminated from
behind by the LED, which is soldered onto the
instrument cluster electronic circuit board. The secu-
rity indicator is serviced as a unit with the instru-
ment cluster.
OPERATION
The security indicator gives an indication to the
vehicle operator when the Vehicle Theft Security Sys-
tem (VTSS) is arming or is armed. On models
equipped with the Sentry Key Immobilizer System
(SKIS), the security indicator also gives an indication
to the vehicle operator of the status of the SKIS. This
indicator is controlled by a transistor on the instru-
ment cluster circuit board based upon cluster pro-
gramming, hard wired inputs to the cluster from the
various security system components, electronic mes-
sages received by the cluster from the Remote Key-
less Entry (RKE) receiver module over a dedicated
serial bus, and electronic messages received by the
cluster from the Sentry Key Immobilizer Module
(SKIM) over the Programmable Communications
Interface (PCI) data bus. The security indicator Light
Emitting Diode (LED) is completely controlled by the
instrument cluster logic circuit, and that logic will
allow this indicator to operate whenever the instru-
ment cluster receives a battery current input on the
fused B(+) circuit. Therefore, the LED can be illumi-
nated regardless of the ignition switch position. The
LED only illuminates when it is provided a path to
ground by the instrument cluster transistor. The
instrument cluster will turn on the security indicator
for the following reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position, the SKIM tells the cluster
to illuminate the SKIS indicator for about two sec-
onds as a bulb test.
²VTSS Indication- During the sixteen second
VTSS arming function, the cluster will flash the
security indicator on and off repeatedly at a steady,
fast rate to indicate that the VTSS is in the process
of arming. Following successful VTSS arming, the
cluster flashes the security indicator on and off con-
tinuously at a slower rate to indicate that the VTSS
is armed. The security indicator continues flashing at
the slower rate until the VTSS is disarmed or trig-
gered. If the VTSS has alarmed and rearmed, the
cluster will flash the security indicator at a steady,
slow rate for about thirty seconds after the VTSS is
disarmed.
²SKIM Lamp-On Message- Each time the clus-
ter receives a lamp-on message from the SKIM, the
security indicator will be illuminated. The indicatorcan be flashed on and off, or illuminated solid, as dic-
tated by the SKIM message. The indicator remains
illuminated solid or continues to flash until the clus-
ter receives a lamp-off message from the SKIM, or
until the ignition switch is turned to the Off position,
whichever occurs first. For more information on the
SKIS and the security indicator control parameters,
(Refer to 8 - ELECTRICAL/VEHICLE THEFT SECU-
RITY/SENTRY KEY IMMOBILIZER SYSTEM -
OPERATION).
²Communication Error- If the cluster receives
no SKIS lamp-on or lamp-off messages from the
SKIM for twenty consecutive seconds, the SKIS indi-
cator is illuminated by the instrument cluster. The
indicator remains controlled and illuminated by the
cluster until a valid SKIS lamp-on or lamp-off mes-
sage is received from the SKIM.
²Actuator Test- Each time the instrument clus-
ter is put through the actuator test, the security indi-
cator will be turned on, then off again during the
bulb check portion of the test to confirm the function-
ality of the LED and the cluster control circuitry.
The instrument cluster circuitry controls the secu-
rity indicator whenever the ignition switch is in the
Off position and the VTSS is arming, armed, or
alarming. Whenever the ignition switch is in the On
or Start positions, the SKIM performs a self-test to
decide whether the SKIS is in good operating condi-
tion and whether a valid key is present in the igni-
tion lock cylinder. The SKIM then sends the proper
lamp-on or lamp-off messages to the instrument clus-
ter. For further diagnosis of the security indicator or
the instrument cluster circuitry that controls the
indicator, (Refer to 8 - ELECTRICAL/INSTRUMENT
CLUSTER - DIAGNOSIS AND TESTING). If the
instrument cluster flashes the SKIS indicator upon
ignition On, or turns on the SKIS indicator solid
after the bulb test, it indicates that a SKIS malfunc-
tion has occurred or that the SKIS is inoperative. For
proper diagnosis of the VTSS, the SKIS, the SKIM,
the PCI data bus, or the electronic message inputs to
the instrument cluster that control the security indi-
cator, a DRBIIItscan tool is required. Refer to the
appropriate diagnostic information.
SERVICE 4WD INDICATOR
DESCRIPTION
A service 4WD indicator is standard equipment on
all instrument clusters. However, on vehicles not
equipped with the optional four-wheel drive system
and electronically shifted transfer case, this indicator
is electronically disabled. The service 4WD indicator
consists of the words ªSERVICE 4x4º, which appears
in the lower portion of the odometer/trip odometer
DRINSTRUMENT CLUSTER 8J - 35
SECURITY INDICATOR (Continued)

Vacuum Fluorescent Display (VFD) unit. The VFD is
soldered onto the cluster electronic circuit board and
is visible through a window with a smoked clear lens
located on the lower edge of the tachometer gauge
dial face of the cluster overlay. The dark lens over
the VFD prevents the indicator from being clearly
visible when it is not illuminated. The words ªSER-
VICE 4x4º appear in an amber color and at the same
lighting level as the odometer/trip odometer informa-
tion when they are illuminated by the instrument
cluster electronic circuit board. The service 4WD
indicator is serviced as a unit with the VFD in the
instrument cluster.
OPERATION
The service 4WD indicator gives an indication to
the vehicle operator when the Transfer Case Control
Module (TCCM) has recorded a Diagnostic Trouble
Code (DTC) for an electronic transfer case circuit or
component malfunction. This indicator is controlled
by a transistor on the instrument cluster circuit
board based upon cluster programming and elec-
tronic messages received by the cluster from the
TCCM over the Programmable Communications
Interface (PCI) data bus. The service 4WD indicator
is completely controlled by the instrument cluster
logic circuit, and that logic will only allow this indi-
cator 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 indicator only illu-
minates when it is switched to ground by the instru-
ment cluster circuitry. The instrument cluster will
turn on the service 4WD indicator for the following
reasons:
²Service 4WD Lamp-On Message- Each time
the cluster receives a service 4WD lamp-on message
from the TCCM, the indicator will be illuminated.
The indicator remains illuminated until the cluster
receives a service 4WD lamp-off message from the
TCCM, or until the ignition switch is turned to the
Off position, whichever occurs first.
²Communication Error- If the cluster receives
no messages from the TCCM for five seconds, the
service 4WD indicator is illuminated by the instru-
ment cluster to indicate a loss of TCCM communica-
tion. The indicator remains controlled and
illuminated by the cluster until a valid message is
received from the TCCM.
²Actuator Test- Each time the cluster is put
through the actuator test, the service 4WD indicator
will be turned on, then off again during the VFD por-
tion of the test to confirm the functionality of the
VFD and the cluster control circuitry.The TCCM continually monitors the electronic
transfer case switch and circuits to determine the
condition of the system. The TCCM then sends the
proper lamp-on or lamp-off messages to the instru-
ment cluster. For further diagnosis of the service
4WD indicator or the instrument cluster circuitry
that controls the VFD, (Refer to 8 - ELECTRICAL/
INSTRUMENT CLUSTER - DIAGNOSIS AND
TESTING). For proper diagnosis of the TCCM, the
PCI data bus, or the electronic message inputs to the
instrument cluster that control the service 4WD indi-
cator, a DRBIIItscan tool is required. Refer to the
appropriate diagnostic information.SPEEDOMETER
DESCRIPTION
A speedometer is standard equipment on all instru-
ment clusters. The speedometer is located next to the
tachometer, just to the right of center in the instru-
ment cluster. The speedometer consists of a movable
gauge needle or pointer controlled by the instrument
cluster circuitry and a fixed 210 degree primary scale
on the gauge dial face that reads left-to-right either
from ª0º to ª120º mph, or from ª0º to ª200º km/h,
depending upon the market for which the vehicle is
manufactured. Each version also has a secondary
inner scale on the gauge dial face that provides the
equivalent opposite units from the primary scale.
Text appearing on the cluster overlay just below the
hub of the speedometer needle abbreviates the unit
of measure for the primary scale (i.e.: MPH or km/h),
followed by the unit of measure for the secondary
scale. The speedometer graphics are black (primary
scale) and blue (secondary scale) against a white
field, making them clearly visible within the instru-
ment cluster in daylight. When illuminated from
behind by the panel lamps dimmer controlled cluster
illumination lighting with the exterior lamps turned
On, the black graphics appear dark blue and the blue
graphics appear light blue. The orange gauge needle
is internally illuminated. Gauge illumination is pro-
vided by replaceable incandescent bulb and bulb
holder units located on the instrument cluster elec-
tronic circuit board. The speedometer is serviced as a
unit with the instrument cluster.
OPERATION
The speedometer gives an indication to the vehicle
operator of the vehicle road speed. This gauge is con-
trolled by 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 Communica-
tions Interface (PCI) data bus. The speedometer is an
8J - 36 INSTRUMENT CLUSTERDR
SERVICE 4WD INDICATOR (Continued)

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:
²Vehicle Speed Message- Each time the clus-
ter receives a vehicle speed message from the PCM it
will calculate the correct vehicle speed reading and
position the gauge needle at that relative speed posi-
tion on the gauge scale. The cluster will receive a
new vehicle speed message and reposition the gauge
pointer accordingly about every 88 milliseconds. The
gauge needle will continue to be positioned at the
actual vehicle speed position on the gauge scale until
the ignition switch is turned to the Off position.
²Communication Error- If the cluster fails to
receive a speedometer message, it will hold the gauge
needle at the last indication for about three seconds,
or until the ignition switch is turned to the Off posi-
tion, whichever occurs first. After three seconds, the
gauge needle will return to the left end of the gauge
scale.
²Actuator Test- Each time the cluster is put
through the actuator test, the speedometer needle
will be swept to several calibration points on the
gauge scale in a prescribed sequence in order to con-
firm the functionality of the gauge and the cluster
control circuitry.
The PCM continually monitors the vehicle speed
sensor to determine the vehicle road speed. The PCM
then sends the proper vehicle speed messages to the
instrument cluster. For further diagnosis of the
speedometer 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 vehicle speed
sensor, the PCM, the PCI data bus, or the electronic
message inputs to the instrument cluster that control
the speedometer, a DRBIIItscan tool is required.
Refer to the appropriate diagnostic information.
TACHOMETER
DESCRIPTION
A tachometer is standard equipment on all instru-
ment clusters. The tachometer is located to the left of
the speedometer, just to the left of center in the
instrument cluster. The tachometer consists of a
movable gauge needle or pointer controlled by the
instrument cluster circuitry and a fixed 210 degree
scale on the gauge dial face that reads left-to-rightfrom ª0º to ª7º for gasoline engines. On vehicles with
a diesel engine, the scale reads from ª0º to ª5º. The
text ªRPM X 1000º imprinted on the cluster overlay
directly below the hub of the tachometer needle iden-
tifies that each number on the tachometer scale is to
be multiplied by 1000 rpm. The tachometer graphics
are black against a white field, making them clearly
visible within the instrument cluster in daylight.
When illuminated from behind by the panel lamps
dimmer controlled cluster illumination lighting with
the exterior lamps turned On, the black graphics
appear blue. The orange gauge needle is internally
illuminated. Gauge illumination is provided by
replaceable incandescent bulb and bulb holder units
located on the instrument cluster electronic circuit
board. The tachometer is serviced as a unit with the
instrument cluster.
OPERATION
The tachometer gives an indication to the vehicle
operator of the engine speed. This gauge is controlled
by the instrument cluster circuit board based upon
cluster programming and electronic messages
received by the cluster from the Powertrain Control
Module (PCM) on vehicles with a gasoline engine, or
from the Engine Control Module (ECM) on vehicles
equipped with a diesel engine over the Programma-
ble Communications Interface (PCI) data bus. The
tachometer is an air core magnetic unit that receives
battery current on the instrument cluster electronic
circuit board through the fused ignition switch out-
put (run-start) circuit whenever the ignition switch is
in the On or Start positions. The cluster is pro-
grammed 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 or
ECM it will calculate the correct engine speed read-
ing and position the gauge needle at that relative
speed position on the gauge scale. The cluster will
receive a new engine speed message and reposition
the gauge pointer accordingly about every 88 milli-
seconds. The gauge needle will continually be reposi-
tioned at the relative engine speed position on the
gauge scale until the engine stops running, or until
the ignition switch is turned to the Off position,
whichever occurs first.
²Communication Error- If the cluster fails to
receive an engine speed message, it will hold the
gauge needle at the last indication for about three
seconds, or until the ignition switch is turned to the
Off position, whichever occurs first. After three sec-
DRINSTRUMENT CLUSTER 8J - 37
SPEEDOMETER (Continued)

onds, the gauge needle will return to the left end of
the gauge scale.
²Actuator Test- Each time the cluster is put
through the actuator test, the tachometer needle will
be swept to several calibration points on the gauge
scale in a prescribed sequence in order to confirm the
functionality of the gauge and the cluster control cir-
cuitry.
On vehicles with a gasoline engine, the PCM con-
tinually monitors the crankshaft position sensor to
determine the engine speed. On vehicles with a die-
sel engine, the ECM continually monitors the engine
speed sensor to determine the engine speed. The
PCM or ECM then sends the proper engine speed
messages to the instrument cluster. For further diag-
nosis of the tachometer or the instrument cluster cir-
cuitry that controls the gauge, (Refer to 8 -
ELECTRICAL/INSTRUMENT CLUSTER - DIAGNO-
SIS AND TESTING). For proper diagnosis of the
crankshaft position sensor, the engine speed sensor,
the PCM, the ECM, the PCI data bus, or the elec-
tronic message inputs to the instrument cluster that
control the tachometer, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
TRANS TEMP INDICATOR
DESCRIPTION
A transmission over-temperature indicator is stan-
dard equipment on all instrument clusters. However,
on vehicles not equipped with an optional automatic
transmission, this indicator is electronically disabled.
The transmission over-temperature indicator is
located on the left side of the instrument cluster, to
the left of the fuel gauge. The transmission over-tem-
perature indicator consists of a stencil-like cutout of
the words ªTRANS TEMPº in the opaque layer of the
instrument cluster overlay. The dark outer layer of
the overlay prevents the indicator from being clearly
visible when it is not illuminated. A red Light Emit-
ting Diode (LED) behind the cutout in the opaque
layer of the overlay causes the ªTRANS TEMPº text
to appear in red through the translucent outer layer
of the overlay when the indicator is illuminated from
behind by the LED, which is soldered onto the
instrument cluster electronic circuit board. The
transmission over-temperature indicator is serviced
as a unit with the instrument cluster.
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 orfailure. This indicator is controlled by a transistor on
the instrument cluster circuit board based upon clus-
ter programming and electronic messages received by
the cluster from the Powertrain Control Module
(PCM) over the Programmable Communications
Interface (PCI) data bus. The transmission over-tem-
perature indicator Light Emitting Diode (LED) is
completely controlled by the instrument cluster logic
circuit, 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 LED 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 transmission over-temperature 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 two sec-
onds as a bulb test.
²Trans Over-Temp Lamp-On Message- Each
time the cluster receives a trans over-temp lamp-on
message from the PCM indicating that the transmis-
sion fluid temperature is 135É C (275É F) or higher,
the indicator will be illuminated and a single chime
tone is sounded. The indicator remains illuminated
until the cluster receives a trans over-temp lamp-off
message from the PCM, or until the ignition switch
is turned to the Off position, whichever occurs first.
The chime tone feature will only repeat during the
same ignition cycle if the transmission over-tempera-
ture indicator is cycled off and then on again by the
appropriate trans over-temp messages from the PCM.
²Actuator Test- Each time the cluster is put
through the actuator test, the transmission over-tem-
perature indicator will be turned on, then off again
during the bulb check portion of the test to confirm
the functionality of the LED and the cluster control
circuitry.
The PCM continually monitors the transmission
temperature sensor to determine the transmission
operating condition. The PCM then sends the proper
trans over-temp lamp-on or lamp-off messages to the
instrument cluster. 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 and/or the transmis-
sion 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 LED, (Refer to 8 -
ELECTRICAL/INSTRUMENT CLUSTER - DIAGNO-
SIS AND TESTING). For proper diagnosis of the
transmission temperature sensor, the PCM, the PCI
8J - 38 INSTRUMENT CLUSTERDR
TACHOMETER (Continued)

data bus, or the electronic message inputs to the
instrument cluster that control the transmission
over-temperature indicator, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
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, between the speedom-
eter and the tachometer. Each turn signal indicator
consists of a stencil-like cutout of the International
Control and Display Symbol icon for ªTurn Warningº
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. A green Light Emitting Diode (LED)
behind each turn signal indicator cutout in the
opaque layer of the overlay causes the icon to appear
in green through the translucent outer layer of the
overlay when the indicator is illuminated from
behind by the LED, which is soldered onto the
instrument cluster electronic circuit board. The turn
signal indicators are serviced as a unit with the
instrument cluster.
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 transis-
tors on the instrument cluster electronic circuit board
based upon the cluster programming, a hard wired
multiplex input received by the cluster from the turn
signal and hazard warning switch circuitry of the
multi-function switch on the turn/hazard switch mux
circuit, and electronic messages received from the
Front Control Module (FCM) over the Programmable
Communications Interface (PCI) data bus. Each turn
signal indicator Light Emitting Diode (LED) is com-
pletely controlled by the instrument cluster logic cir-
cuit, and that logic will allow this indicator to
operate whenever the instrument cluster receives a
battery current input on the fused B(+) circuit.
Therefore, each LED can be illuminated regardless of
the ignition switch position. The LED only illumi-
nates when it is provided a path to ground by the
instrument cluster transistor. The instrument cluster
will turn on the turn signal indicators for the follow-
ing reasons:²Turn Signal-On Input- Each time the cluster
detects a turn signal-on input from the turn signal
switch circuitry of the multi-function switch on the
turn/hazard switch mux circuit, the requested turn
signal lamps and turn signal indicator will be flashed
on and off, and an electromechanical relay soldered
onto the cluster electronic circuit board will produce
a clicking sound to emulate a conventional turn sig-
nal flasher. The turn signals and the turn signal
indicators continue to flash on and off until the clus-
ter receives a turn signal-off input from the multi-
function switch, or until the ignition switch is turned
to the Off position, whichever occurs first. The
instrument cluster also sends an electronic message
to the FCM over the PCI data bus, and the FCM
flashes the appropriate exterior turn signal lamps. If
the FCM detects an inoperative turn signal circuit, it
increases the flash rate for the remaining operative
turn signals and sends an electronic message to the
instrument cluster. The instrument cluster then
increases the flash rate of the turn signal indicator
and the clicking rate of the electromechanical relay
to provide an indication of the problem to the vehicle
operator.
²Hazard Warning-On Input- Each time the
cluster detects a hazard warning-on input from the
hazard warning switch circuitry of the multi-function
switch on the turn/hazard switch mux circuit, all of
the turn signal lamps and both turn signal indicators
will be flashed on and off, and an electromechanical
relay soldered onto the cluster electronic circuit
board will produce a clicking sound to emulate a con-
ventional hazard warning flasher. The turn signals
and the turn signal indicators continue to flash on
and off until the cluster receives a hazard warning-
off input from the multi-function switch. The instru-
ment cluster also sends an electronic message to the
FCM over the PCI data bus, and the FCM flashes all
of the exterior turn signal lamps. If the FCM detects
an inoperative turn signal circuit, it increases the
flash rate for the remaining operative turn signals
and sends an electronic message to the instrument
cluster. The instrument cluster then increases the
flash rate of both turn signal indicators and the click-
ing rate of the electromechanical relay to provide an
indication of the problem to the vehicle operator.
²Actuator Test- Each time the cluster is put
through the actuator test, the turn signal indicators
will be turned on, then off again during the bulb
check portion of the test to confirm the functionality
of each LED and the cluster control circuitry.
The instrument cluster continually monitors the
multi-function switch to determine the proper turn
signal and hazard warning system control. The
instrument cluster then sends the proper turn signal
and hazard warning flasher-on and flasher-off mes-
DRINSTRUMENT CLUSTER 8J - 39
TRANS TEMP INDICATOR (Continued)

reads from ª8º to ª18º volts. An International Control
and Display Symbol icon for ªBattery Charging Con-
ditionº is located on the cluster overlay, directly
below the right end of the gauge scale. The voltage
gauge graphics are black against a white field except
for a single red graduation at each end of the gauge
scale, making them clearly visible within the instru-
ment cluster in daylight. When illuminated from
behind by the panel lamps dimmer controlled cluster
illumination lighting with the exterior lamps turned
On, the black graphics appear blue and the red
graphics still appear red. The orange gauge needle is
internally illuminated. Gauge illumination is pro-
vided by replaceable incandescent bulb and bulb
holder units located on the instrument cluster elec-
tronic circuit board. The voltage gauge is serviced as
a unit with the instrument 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) on vehicles
equipped with a gasoline engine, or from the Engine
Control Module (ECM) on vehicles equipped with a
diesel engine over the Programmable Communica-
tions Interface (PCI) data bus. The voltage gauge is
an air core magnetic unit that receives battery cur-
rent 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 left 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:
²System Voltage Message- Each time the clus-
ter receives a system voltage message from the PCM
or ECM indicating the system voltage is between
about 9.5 volts and about 15 volts, the gauge needle
is moved to the relative voltage position on the gauge
scale.
²System Voltage Low (Charge Fail) Message
- Each time the cluster receives three consecutive
messages from the PCM or ECM indicating the elec-
trical system voltage is less than about 9 volts
(charge fail condition), the gauge needle is moved to
the graduation on the far left end of the gauge scale
and the check gauges indicator is illuminated. The
gauge needle remains at the far left end of the gauge
scale and the check gauges indicator remains illumi-
nated until the cluster receives a single message
from the PCM or ECM indicating the electrical sys-tem voltage is greater than about 9.5 volts (but less
than about 15.5 volts), or until the ignition switch is
turned to the Off position, whichever occurs first. On
vehicles equipped with the optional diesel engine, the
ECM is programmed to restrict the voltage gauge
needle to a position above the graduation on the far
left end of the gauge scale and suppress the check
engine indicator operation until after the engine
intake manifold air heater has completed a pre-heat
or post-heat cycle.
²System Voltage High Message- Each time
the cluster receives three consecutive messages from
the PCM or ECM indicating the electrical system
voltage is greater than about 15.5 volts, the gauge
needle is moved to the graduation on the far right
end of the gauge scale and the check gauges indica-
tor is illuminated. The gauge needle remains at the
right end of the gauge scale and the check gauges
indicator remains illuminated until the cluster
receives a message from the PCM or ECM indicating
the electrical system voltage is less than about 15.0
volts (but greater than about 9.5 volts), or until the
ignition switch is turned to the Off position, which-
ever occurs first.
²Communication Error- If the cluster fails to
receive a system voltage message, it will hold the
gauge needle at the last indication for about five sec-
onds or until the ignition switch is turned to the Off
position, whichever occurs first. After five seconds,
the cluster will move the gauge needle to the far left
end of the gauge scale.
²Actuator Test- Each time the cluster is put
through the actuator test, the voltage gauge needle
will be swept to several calibration points on the
gauge scale in a prescribed sequence in order to con-
firm the functionality of the gauge and the cluster
control circuitry.
On vehicles with a gasoline engine, the PCM con-
tinually monitors the system voltage to control the
generator output. On vehicles with a diesel engine,
the ECM continually monitors the system voltage to
control the generator output. The PCM or ECM then
sends the proper system voltage messages to the
instrument cluster. For further diagnosis of the volt-
age gauge or the instrument cluster circuitry that
controls the gauge, (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND TEST-
ING). If the instrument cluster turns on the check
gauges indicator due to a charge fail or voltage high
condition, it may indicate that the charging system
requires service. For proper diagnosis of the charging
system, the PCM, the ECM, the PCI data bus, or the
electronic message inputs to the instrument cluster
that control the voltage gauge, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
DRINSTRUMENT CLUSTER 8J - 41
VOLTAGE GAUGE (Continued)