Vacuum DODGE RAM 1500 1998 2.G Owner's Manual

²Engine Temperature High Message- Each
time the cluster receives a message from the PCM or
ECM indicating the engine coolant temperature of a
gasoline engine is about 122É C (252É F) or higher, or
of a diesel engine is about 112É C (233É F) or higher,
the check gauges indicator will be illuminated. The
indicator remains illuminated until the cluster
receives a message from the PCM or ECM indicating
that the engine coolant temperature of a gasoline
engine is below about 122É C (252É F), or of a diesel
engine is below about 112É C (233É F), or until the
ignition switch is turned to the Off position, which-
ever occurs first.
²Engine Oil Pressure Low Message- Each
time the cluster receives a message from the PCM or
ECM indicating the engine oil pressure is about 41
kPa (6 psi) or lower, the check gauges indicator will
be illuminated. The indicator remains illuminated
until the cluster receives a message from the PCM or
ECM indicating that the engine oil pressure is above
about 41 kPa (6 psi), or until the ignition switch is
turned to the Off position, whichever occurs first.
The cluster will only turn the indicator on in
response to an engine oil pressure low message if the
engine speed is greater than zero.
²System Voltage Low (Charge Fail) Message
- Each time the cluster receives a message from the
PCM or ECM indicating the electrical system voltage
is less than about 11.5 volts (charge fail condition),
the check gauges indicator will be illuminated. The
indicator remains illuminated until the cluster
receives a message from the PCM or ECM indicating
the electrical system voltage is greater than about
12.0 volts (but less than 16.0 volts), or until the igni-
tion switch is turned to the Off position, whichever
occurs first.
²System Voltage High Message- Each time
the cluster receives a message from the PCM or ECM
indicating the electrical system voltage is greater
than about 16.0 volts, the check gauges indicator will
be illuminated. The indicator remains illuminated
until the cluster receives a message from the PCM or
ECM indicating the electrical system voltage is less
than about 15.5 volts (but greater than 11.5 volts), 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 check gauges 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.
On vehicles with a gasoline engine, the PCM con-
tinually monitors the engine temperature, oil pres-
sure, and electrical system voltage, then sends the
proper messages to the instrument cluster. On vehi-
cles with a diesel engine, the ECM continually mon-itors the engine temperature, oil pressure, and
electrical system voltage, then sends the proper mes-
sages to the instrument cluster. For further diagnosis
of the check gauges indicator or the instrument clus-
ter circuitry that controls the LED, (Refer to 8 -
ELECTRICAL/INSTRUMENT CLUSTER - DIAGNO-
SIS AND TESTING). For proper diagnosis of the
PCM, the ECM, the PCI data bus, or the electronic
message inputs to the instrument cluster that control
the check gauges indicator, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
CRUISE INDICATOR
DESCRIPTION
A cruise indicator is standard equipment on all
instrument clusters (Fig. 13). However, on vehicles
not equipped with the optional speed control system,
this indicator is electronically disabled. The cruise
indicator consists of the word ªCRUISEº, which
appears in the lower portion of the gear selector indi-
cator 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 speedom-
eter 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 word
ªCRUISEº appears in a blue-green color and at the
same lighting level as the gear selector indicator
information when it is illuminated by the instrument
cluster electronic circuit board. The cruise indicator
is serviced as a unit with the VFD in the instrument
cluster.
OPERATION
The cruise indicator gives an indication to the vehi-
cle operator when the speed control system is turned
On, regardless of whether the speed control is
engaged. This indicator is controlled by the instru-
ment cluster circuit board based upon cluster pro-
gramming and electronic messages received by the
cluster from the Powertrain Control Module (PCM)
over the Programmable Communications Interface
(PCI) data bus. The cruise indicator 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 battery cur-
rent input on the fused ignition switch output (run-
start) circuit. Therefore, the indicator will always be
Fig. 13 Cruise Indicator
8J - 22 INSTRUMENT CLUSTERDR
CHECK GAUGES INDICATOR (Continued)

the PCM or ECM indicating the percent tank full is
less than empty, the gauge needle is moved to the far
left end of the gauge scale and the low fuel indicator
is illuminated immediately. This message would indi-
cate that the fuel tank sender input to the PCM or
ECM is a short circuit.
²More Than Full Percent Tank Full Message
- Each time the cluster receives a message from the
PCM or ECM indicating the percent tank full is more
than full, the gauge needle is moved to the far left
end of the gauge scale and the low fuel indicator is
illuminated immediately. This message would indi-
cate that the fuel tank sender input to the PCM or
ECM is an open circuit.
²Communication Error- If the cluster fails to
receive a percent tank full message, it will hold the
gauge needle at the last indication about five seconds
or until the ignition switch is turned to the Off posi-
tion, whichever occurs first. After five seconds, the
cluster will move the gauge needle to the low end of
the gauge scale.
²Actuator Test- Each time the cluster is put
through the actuator test, the fuel gauge 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 fuel tank sending unit to deter-
mine the level of the fuel in the fuel tank. On
vehicles with a diesel engine, the ECM continually
monitors the fuel tank sending unit to determine the
level of the fuel in the fuel tank. The PCM or ECM
then sends the proper fuel level messages to the
instrument cluster. For further diagnosis of the fuel
gauge or the instrument cluster circuitry that con-
trols the gauge, (Refer to 8 - ELECTRICAL/INSTRU-
MENT CLUSTER - DIAGNOSIS AND TESTING).
For proper diagnosis of the fuel tank sending unit,
the PCM, the ECM, the PCI data bus, or the elec-
tronic message inputs to the instrument cluster that
control the fuel gauge, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
GEAR SELECTOR INDICATOR
DESCRIPTION
An electronic automatic transmission gear selector
indicator is standard factory-installed equipment onthis model. The gear selector indicator information is
displayed in a 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
speedometer 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 gear selector indicator displays the following
characters from left to right: ªP,º ªR,º ªN,º ªD,º ª2,º
and ª1º (Fig. 18). Respectively, these characters rep-
resent the park, reverse, neutral, drive, second gear,
and first gear positions of the transmission gear
selector lever on the steering column. The VFD illu-
minates a rectangular box around the character that
represents the currently selected lever position.
The gear selector indicator characters and graphics
appear in the same blue-green color and at the same
lighting level as the odometer/trip odometer informa-
tion when illuminated by the instrument cluster elec-
tronic circuit board. During daylight hours (exterior
lamps Off) the gear selector indicator VFD is illumi-
nated at full brightness for clear visibility. At night
(exterior lamps are On) the VFD lighting level is
adjusted with the other cluster illumination lamps
using the panel lamps dimmer thumbwheel on the
headlamp switch. However, a ªParadeº mode position
of the panel lamps dimmer thumbwheel allows the
VFD to be illuminated at full brightness when the
vehicle is driven in daylight hours with the exterior
lamps turned On. The gear selector indicator VFD is
serviced as a unit with the instrument cluster.
OPERATION
The electronic gear selector indicator gives an indi-
cation to the vehicle operator of the transmission
gear that has been selected with the automatic trans-
mission gear selector lever. This indicator is con-
trolled by the instrument cluster circuit board based
upon cluster programming. The cluster circuitry
automatically configures itself for the proper trans-
mission and automatic transmission model based
upon the hard wired transmission range sensor mux
circuit input to the cluster. The gear selector indica-
tor information is displayed by a dedicated Vacuum
Fluorescent Display (VFD) unit on the instrument
cluster electronic circuit board, and the VFD will not
display the gear selector indicator information after
the ignition switch is turned to the Off position. The
instrument cluster circuitry configures the gear selec-
tor indicator VFD based upon the following inputs
from the transmission range sensor:
²Open Circuit- If the cluster is configured for
an automatic transmission and the transmission
range sensor mux circuit is open, the cluster circuitry
controls the gear selector indicator display based
Fig. 18 Gear Selector Indicator
DRINSTRUMENT CLUSTER 8J - 27
FUEL GAUGE (Continued)

ODOMETER
DESCRIPTION
An odometer and trip odometer are standard
equipment in all instrument clusters (Fig. 23). The
odometer, trip odometer, and engine hours informa-
tion are displayed in a common electronic, blue-green
Vacuum-Fluorescent Display (VFD). The VFD is sol-
dered 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 it from being clearly visible when
it is not illuminated. However, the odometer, trip
odometer, and engine hours information are not dis-
played simultaneously. The trip odometer reset
switch on the instrument cluster circuit board toggles
the display between odometer and trip odometer
modes by depressing the odometer/trip odometer
switch button that extends through the lower edge of
the cluster lens, just left of the odometer VFD. When
the trip odometer information is displayed, the word
ªTRIPº is also illuminated in the upper right corner
of the VFD in a blue-green color and at the same
lighting level as the trip odometer information. The
engine hours information replaces the selected odom-
eter or trip odometer information whenever the igni-
tion switch is in the On position and the engine is
not running.
The odometer, trip odometer, and engine hours
information is stored in the instrument cluster mem-
ory. This information can be increased when the
proper inputs are provided to the instrument cluster,
but the information cannot be decreased. The odom-
eter can display values up to 999,999 kilometers
(999,999 miles). The odometer latches at these val-
ues, and will not roll over to zero. The trip odometer
can display values up to 9,999.9 kilometers (9,999.9
miles) before it rolls over to zero. The odometer dis-
play does not have a decimal point and will not show
values less than a full unit (kilometer or mile), while
the trip odometer display does have a decimal point
and will show tenths of a unit (kilometer or mile).
The unit of measure (kilometers or miles) for the
odometer and trip odometer display is not shown in
the VFD. The unit of measure for the instrument
cluster odometer/trip odometer is selected at the time
that it is manufactured, and cannot be changed.
Engine hours are displayed in the format, ªhr9999º.The cluster will accumulate values up to 9,999 hours
before the display rolls over to zero.
The odometer has a ªRental Carº mode, which will
illuminate the odometer information in the VFD
whenever the driver side front door is opened with
the ignition switch in the Off or Accessory positions.
During daylight hours (exterior lamps are Off) the
VFD is illuminated at full brightness for clear visibil-
ity. At night (exterior lamps are On) the VFD lighting
level is adjusted with the other cluster illumination
lamps using the panel lamps dimmer thumbwheel on
the headlamp switch. However, a ªParadeº mode
position of the panel lamps dimmer thumbwheel
allows the VFD to be illuminated at full brightness if
the exterior lamps are turned On during daylight
hours.
The VFD, the trip odometer switch, and the trip
odometer switch button are serviced as a unit with
the instrument cluster.
OPERATION
The odometer and trip odometer give an indication
to the vehicle operator of the distance the vehicle has
traveled. The engine hours give an indication of the
cumulative engine-on time. This indicator is con-
trolled by the instrument cluster circuitry 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 odometer, trip
odometer and engine hours information is displayed
by the instrument cluster Vacuum Fluorescent Dis-
play (VFD). The VFD will display the odometer infor-
mation whenever any door is opened with the
ignition switch in the Off or Accessory positions, and
will display the last previously selected odometer or
trip odometer information when the ignition switch is
turned to the On or Start positions. The instrument
cluster circuitry controls the VFD and provides the
following features:
²Odometer/Trip Odometer Display Toggling-
Actuating the trip odometer reset switch button
momentarily with the VFD illuminated will toggle
the display between the odometer and trip odometer
information. Each time the VFD is illuminated with
the ignition switch in the On or Start positions, the
display will automatically return to the last mode
previously selected (odometer or trip odometer).
²Engine Hours Display Toggling- When the
trip odometer reset switch button is pressed and held
for longer than about six seconds with the ignition
switch in the On position and the engine speed mes-
sage from the PCM is zero, the trip odometer infor-
mation will be momentarily displayed, then the
engine hours information will be displayed. The VFD
must be displaying the odometer information when
Fig. 23 Odometer Display
8J - 32 INSTRUMENT CLUSTERDR

appears in the lower portion of the odometer/trip
odometer Vacuum Fluorescent Display (VFD) unit.
The VFD is soldered onto the cluster electronic cir-
cuit 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
text ªSERV 4WDº appears in an amber color and at
the same lighting level as the odometer/trip odometer
information when they are illuminated by the instru-
ment 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 (Fig. 28). The speedometer graphics are black
(primary scale) and blue (secondary scale) 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 dark blue and
the blue graphics appear light blue. The orange
gauge needle is internally illuminated. Gauge illumi-
nation is provided by replaceable incandescent bulb
and bulb holder units located on the instrument clus-
ter electronic circuit board. The speedometer is ser-
viced 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-
Fig. 28 Speedometer Text
DRINSTRUMENT CLUSTER 8J - 37
SERVICE 4WD INDICATOR (Continued)

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-
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.
TOW/HAUL INDICATOR
DESCRIPTION
A tow/haul indicator is standard equipment on all
instrument clusters (Fig. 30). However, on vehicles
not equipped with the optional overdrive automatic
transmission, this indicator is electronically disabled.
The tow/haul indicator consists of the text ªTOW/
HAULº, which appears in the lower portion of the
odometer/trip odometer indicator Vacuum Fluores-
cent 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 VFDprevents the indicator from being clearly visible
when it is not illuminated. The text ªTOW/HAULº
appear in an amber color and at the same lighting
level as the odometer/trip odometer information
when they are illuminated by the instrument cluster
electronic circuit board. The tow/haul indicator is ser-
viced as a unit with the VFD in the instrument clus-
ter.
OPERATION
The tow/haul indicator gives an indication to the
vehicle operator when the Off position of the tow/
haul switch has been selected, disabling the electron-
ically controlled overdrive feature of the automatic
transmission. This indicator 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) over the Programmable Communications
Interface (PCI) data bus. The tow/haul indicator 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 indicator will
always be off when the ignition switch is in any posi-
tion except On or Start. The indicator only illumi-
nates when it is switched to ground by the
instrument cluster circuitry. The instrument cluster
will turn on the tow/haul off indicator for the follow-
ing reasons:
²Tow/Haul Lamp-On Message- Each time the
cluster receives a tow/haul lamp-on message from the
PCM indicating that the Off position of the tow/haul
switch has been selected, the tow/haul indicator will
be illuminated. The indicator remains illuminated
until the cluster receives a tow/haul lamp-off mes-
sage from the PCM, 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 tow/haul indicator will
be turned on, then off again during the VFD portion
of the test to confirm the functionality of the VFD
and the cluster control circuitry.
The PCM continually monitors the tow/haul switch
to determine the proper outputs to the automatic
transmission. The PCM then sends the proper tow/
haul lamp-on and lamp-off messages to the instru-
ment cluster. For further diagnosis of the tow/haul
indicator or the instrument cluster circuitry that con-
trols the indicator, (Refer to 8 - ELECTRICAL/IN-
STRUMENT 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 tow/haul indicator, a DRBIIItscan tool is
Fig. 30 Tow/Haul Indicator
DRINSTRUMENT CLUSTER 8J - 39
TACHOMETER (Continued)

cator is electronically disabled. The upshift indicator
consists of an upward pointed arrow icon, which
appears on the right side of the electronic gear selec-
tor indicator 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
speedometer 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 icon appears in a blue-green color and at the
same lighting level as the odometer/trip odometer
information when it is illuminated by the instrument
cluster electronic circuit board. The upshift indicator
is serviced as a unit with the instrument cluster.
OPERATION
The upshift indicator gives an indication to the
vehicle operator when the manual transmission
should be shifted to the next highest gear in order to
achieve the best fuel economy. This indicator 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) on vehicles with a gasoline engine, or
from the Engine Control Module (ECM) on vehicles
with a diesel engine over the Programmable Commu-
nications Interface (PCI) data bus. The upshift indi-
cator 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 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 indicator only
illuminates when it is switched to ground by the
instrument cluster circuitry. The instrument cluster
will turn on the upshift indicator for the following
reasons:
²Upshift Lamp-On Message- Each time the
cluster receives an upshift lamp-on message from the
PCM or ECM indicating the engine speed and load
conditions are right for a transmission upshift to
occur, the upshift indicator is illuminated. The indi-
cator remains illuminated until the cluster receives
an upshift lamp-off message from the PCM or ECM,
or until the ignition switch is turned to the Off posi-
tion, whichever occurs first. The PCM or ECM will
normally send an upshift lamp-off message three to
five seconds after a lamp-on message, if an upshift is
not performed. The indicator will then remain off
until the vehicle stops accelerating and is brought
back into the range of indicator operation, or until
the transmission is shifted into another gear.
²Actuator Test- Each time the cluster is put
through the actuator test, the upshift indicator willbe turned on, then off again during the VFD portion
of the test to confirm the functionality of the VFD
and the cluster control circuitry.
On vehicles with a gasoline engine, the PCM con-
tinually monitors the engine speed and load condi-
tions to determine the proper fuel and ignition
requirements. On vehicles with a diesel engine, the
ECM continually monitors the engine speed and load
conditions to determine the proper fuel requirements.
The PCM or ECM then sends the proper upshift indi-
cator lamp-on and lamp-off messages to the instru-
ment cluster. For further diagnosis of the upshift
indicator or the instrument cluster circuitry that con-
trols the indicator, (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND
TESTING). For proper diagnosis of the PCM, the
ECM, the PCI data bus, or the electronic message
inputs to the instrument cluster that control the
upshift indicator, a DRBIIItscan tool is required.
Refer to the appropriate diagnostic information.
VOLTAGE GAUGE
DESCRIPTION
A voltage gauge is standard equipment on all
instrument clusters. The voltage gauge is located in
the upper left quadrant of the instrument cluster,
above the fuel gauge. 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 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 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 (Fig. 34). 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 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 voltage gauge is serviced as
a unit with the instrument cluster.
Fig. 34 Battery Charging Condition Icon
8J - 42 INSTRUMENT CLUSTERDR
UPSHIFT INDICATOR (Continued)

BRAKE LAMP
REMOVAL
REMOVAL - WITH CARGO BOX
(1) Disconnect and isolate the negative battery
cable.
(2) Remove the tail lamp unit (Refer to 8 - ELEC-
TRICAL/LAMPS/LIGHTING - EXTERIOR/TAIL
LAMP UNIT - REMOVAL).
(3) Remove the lamp back plate from the tail lamp
unit.
(4) Release the brake lamp bulb locking tabs and
remove the bulb from the back plate.
REMOVAL - WITHOUT CARGO BOX
(1) Disconnect and isolate the negative battery
cable.
(2) Remove the four screws that secure the tail
lamp lens to the tail lamp housing (Fig. 3).
(3) Separate the tail lamp lens from the tail lamp
housing.
(4) Push the brake lamp bulb inward and rotate it
counter-clockwise.
(5) Remove the brake lamp bulb from the brake
lamp socket.
INSTALLATION
INSTALLATION - WITH CARGO BOX
(1) Install the brake lamp bulb into the lamp back
plate.
(2) Install the lamp back plate onto the tail lamp
unit.
(3) Install the tail lamp unit (Refer to 8 - ELEC-
TRICAL/LAMPS/LIGHTING - EXTERIOR/TAIL
LAMP UNIT - INSTALLATION).
(4) Reconnect the negative battery cable.
INSTALLATION - WITHOUT CARGO BOX
(1) Install the brake lamp bulb into the brake
lamp socket by pushing inward and rotating it clock-
wise.
NOTE: Install the tail lamp lens with the clear por-
tion (back-up lens) at the top of the housing. Make
sure that the gasket is correctly in place and not
twisted or torn.
(2) Position the tail lamp lens and gasket onto the
tail lamp unit.
NOTE: Do not overtighten the tail lamp lens screws
or damage to the tail lamp lens may result.
(3) Install the four screws that secure the tail
lamp lens to the tail lamp unit. Tighten the screws
securely.
(4) Reconnect the negative battery cable.
BRAKE LAMP SWITCH
DESCRIPTION
The plunger type brake lamp switch is mounted on
a bracket attached to the base of the steering col-
umn, under the instrument panel.
CAUTION: The switch can only be adjusted during
initial installation. If the switch is not adjusted prop-
erly a new switch must be installed.
OPERATION
The brake lamp switch is hard wired to the Center
High Mount Stop Lamp (CHMSL) and also moni-
tored by the Instrument Cluster for use by the brake
lamp, speed control brake sensor circuits and elec-
tronic brake distribution (EBD). The brake lamp cir-
cuit is open until the plunger is depressed. The speed
control and brake sensor circuits are closed until the
plunger is depressed. When the brake lamp switch
transitions, the CHMSL transitions and instrument
cluster transmits a brake applied/released message
on the bus. The Integrated Power Module (IPM) will
then transition the brake lamps.
When the brake light switch is activated, the Pow-
ertrain Control Module (PCM) receives an input indi-
cating that the brakes are being applied. After
receiving this input, the PCM maintains idle speed to
a scheduled rpm through control of the Idle Air Con-
trol (IAC) motor. The brake switch input is also used
to disable vent and vacuum solenoid output signals
to the speed control servo.
Fig. 3 Tail Lamp Lens
DRLAMPS/LIGHTING - EXTERIOR 8L - 9

Vehicles equipped with the speed control option use
a dual function brake lamp switch. The PCM moni-
tors the state of the dual function brake lamp switch.
The brake switch is equipped with three sets of
contacts, one normally open and the other two nor-
mally closed (brakes disengaged). The PCM sends a
12 volt signal to one of the normally closed contacts
in the brake switch, which is returned to the PCM as
a brake switch state signal. With the contacts closed,
the 12 volt signal is pulled to ground causing the sig-
nal to go low. The low voltage signal, monitored by
the PCM, indicates that the brakes are not applied.
When the brakes are applied, the contacts open,
causing the PCM's output brake signal to go high,
disengaging the speed control, cutting off PCM power
to the speed control solenoids.
The second set of normally closed contacts supplies
12 volts from the PCM any time speed control is
turned on. Through the brake switch, voltage is
routed to the speed control servo solenoids. The
speed control solenoids (vacuum, vent and dump) are
provided this voltage any time the speed control is
ON and the brakes are disengaged.
When the driver applies the brakes, the contacts
open and voltage is interrupted to the solenoids. The
normally open contacts are fed battery voltage. When
the brakes are applied, battery voltage is supplied to
the brake lamps.
The brake lamp switch can only be adjusted once.
That is at the initial installation of the switch. If the
switch is not adjusted properly or has been removed,
a new switch must be installed and adjusted.
DIAGNOSIS AND TESTING - BRAKE LAMP
SWITCH
The brake lamp switch can be tested with an ohm-
meter. The ohmmeter is used to check continuity
between the pin terminals (Fig. 4).
SWITCH CIRCUIT IDENTIFICATION
²Terminals 1 and 2: brake lamp circuit
²Terminals 3 and 4: RWAL/ABS module and Pow-
ertrain Control Module (PCM) circuit
²Terminals 5 and 6: speed control circuit
SWITCH CONTINUITY TEST
NOTE: Disconnect switch harness before testing
switch continuity.
With switch plunger extended, attach test leads to
pins 1 and 2. Replace switch if meter indicates no
continuity.
With switch plunger retracted, attach test leads to
pins 3 and 4. Replace switch if meter indicates no
continuity.With switch plunger retracted, attach test leads to
pins 5 and 6. Replace switch if meter indicates no
continuity.
REMOVAL
(1) Disconnect the switch harness (Fig. 5).
(2) Press and hold the brake pedal in applied posi-
tion.
(3) Rotate the switch counterclockwise about 30É to
align the switch lock tab with the notch in bracket.
(4) Pull the switch rearward out of the mounting
bracket and release the brake pedal.
Fig. 4 Brake Lamp Switch Terminal Identification
1 - TERMINAL PINS
2 - PLUNGER TEST POSITIONS
Fig. 5 Brake Lamp Switch & Bracket
1 - RELEASE LEVER
2 - BRACKET
3 - BRAKE PEDAL SUPPORT
4 - BRAKE LAMP SWITCH
8L - 10 LAMPS/LIGHTING - EXTERIORDR
BRAKE LAMP SWITCH (Continued)

The compass unit also will compensate for magne-
tism the body of the vehicle may acquire during nor-
mal use. However, avoid placing anything magnetic
directly on the roof of the vehicle. Magnetic mounts
for an antenna, a repair order hat, or a funeral pro-
cession flag can exceed the compensating ability of
the compass unit if placed on the roof panel. Mag-
netic bit drivers used on the fasteners that hold the
overhead console assembly to the roof header can
also affect compass operation. If the vehicle roof
should become magnetized, the demagnetizing and
calibration procedures found in this section may be
required to restore proper compass operation.
TEMPERATURE DISPLAY
All the available overhead consoles on this model
include Temperature information. The temperature
displays the outside ambient temperature in whole
degrees. The temperature display can be toggled
from Fahrenheit to Celsius by selecting the desired
U.S./Metric option from the customer programmable
features. The displayed temperature is not an instant
reading of conditions, but an average temperature. It
may take the temperature display several minutes to
respond to a major temperature change, such as driv-
ing out of a heated garage into winter temperatures.
When the ignition switch is turned to the Off posi-
tion, the last displayed temperature reading stays in
the electronic control modules, (CMTC, EVIC) mem-
ory. When the ignition switch is turned to the On
position again, the electronic module will display the
memory temperature for one minute; then update the
display to the current average temperature reading
within five minutes.The temperature function is supported by an ambi-
ent temperature sensor. This sensor is mounted out-
side the passenger compartment near the front and
center of the vehicle, and is hard wired to the Front
Control Module (FCM). The FCM sends temperature
status messages to the module over the J1850 PCI
data bus circuit. For more information on the ambi-
ent temperature sensor, refer to Ambient Tempera-
ture Sensor later in this section.
Following are general descriptions of the major
components used in the overhead console. Refer to
Wiring Diagrams for complete circuit schematics.
OPERATION
Refer to the vehicle Owner's Manual for specific
operation of each overhead console and its systems.
DIAGNOSIS AND TESTING - OVERHEAD
CONSOLE
If the problem with the overhead console is an
inaccurate or scrambled display, refer toSELF-DI-
AGNOSTIC TESTlater in this text. If the problem
with the overhead console is incorrect Vacuum Fluo-
rescent Display (VFD) dimming levels, use a DRB
IIItscan tool and the proper Diagnostic Procedures
manual to test for the correct dimming message
inputs being received from the Body Control Module
(BCM) or Front Control Module (FCM) over the
J1850 Programmable Communications Interface
(PCI) data bus circuit. If the problem is a no-display
condition, use the following procedure. For complete
circuit diagrams, refer toOverhead Consolein the
Wiring Diagrams section of the service manual.
(1) Remove the overhead console from the head-
liner (Refer to 8 - ELECTRICAL/OVERHEAD CON-
SOLE - REMOVAL).
(2) Check for battery voltage at the overhead con-
sole electrical connector. Refer to Wiring for connec-
tor information. If OK, go to Step 3. If not OK, Check
for battery voltage at the appropriate B(+) fuse in the
integrated power module, repair the open fused B(+)
circuit as required.
(3) Turn the ignition switch to the On position.
Check the fused ignition switch output circuit(s) at
the overhead console electrical connector. If OK, go to
Step 4. If not OK, repair the open or shorted circuit
as required.
(4) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Check for continuity between the ground circuit cav-
ity of the overhead console electrical connector and a
good ground. There should be continuity. If OK, refer
toSELF-DIAGNOSTIC TESTbelow for further
diagnosis of the electronics module and the J1850
PCI data bus circuit. If not OK, repair the open
ground circuit as required.
Fig. 1 DR OVERHEAD CONSOLE ± EVIC
8M - 2 MESSAGE SYSTEMSDR
OVERHEAD CONSOLE (Continued)

(6) Depress and release theRESETpush button
to enter the displayed zone number into the EVIC/
CMTC module memory.
(7) Confirm that the correct directions are now
indicated by the compass.
REMOVAL
OVERHEAD CONSOLE REMOVAL
(1) Disconnect and isolate the negative battery
cable.
(2) Remove the overhead console retaining screws,
located in the sunglass storage bin.
(3) Using your fingertips, grasp the sides of the
overhead console and pull straight down evenly to
disengage the two snap clips at the front of the unit.
(4) Lower the overhead console far enough to
access the wire harness connectors.
(5) Disconnect the EVIC, CMTC electronic module
and the reading/courtesy lamps electrical connectors.
(6) Remove the overhead console from the vehicle.
INSTALLATION
(1) Position the overhead console in the vehicle.
(2) Connect the EVIC, CMTC electronic module
and the reading/courtesy lamps electrical connectors.
(3) Grasp the sides of the overhead console and
push straight up evenly to engage the two snap clips
at the rear of the unit.
(4) Install the overhead console retaining screw,
located in the front of console. Torque the screw to
1.2 N´m (10 in. lbs.).
(5) Connect the negative battery cable.
COMPASS/MINI-TRIP
COMPUTER
DESCRIPTION
The Compass Mini-Trip Computer (CMTC) is a
module located in the overhead console. The CMTC is
equipped with a mini-trip feature. The CMTC con-
sists of a electronic control module with a vacuum
fluorescent display (VFD) and function switches. The
CMTC consists of a electronic module that displays
compass, trip computer, and temperature features.
Actuating the STEP push button will cause the
CMTC to change mode of operation when the ignition
is ON. Example:
²Average miles per gallon (ECO)
²Distance to empty (DTE)
²Trip odometer (ODO)
²Elapsed time (ET)
²OffActuating the C/T push button will cause the
CMTC to change to Compass/Temperature display.
OPERATION
The Compass Mini-Trip Computer module in the
overhead console has buttons used to select various
functions. The CMTC selector buttons will not oper-
ate until the ignition is in the RUN position.
When the ignition switch is first turned to the
RUN position the CMTC display;
²Returns to the last mode setting selected before
the ignition was last switched OFF.
DIAGNOSIS AND TESTING - COMPASS
MINI-TRIP COMPUTER
Compass Mini-Trip Computer (CMTC) data is
obtained from other electronic modules (CCN, FCM
and JTEC) on the J1850 Data Bus circuit. The
CMTC will display dashes (- -) for any of the screens
it did not receive the bus messages. The label corre-
sponding to the missing information will be lit. If no
compass mini-trip computer data is displayed, check
the J1850 Data Bus circuit communications and the
other modules.
Refer to Overhead Console Diagnosis and Testing
for instructions on performing a CMTC module Self-
Diagnostic Test. The DRB IIItis recommended for
checking the J1850 Data Bus circuit and the other
modules. Perform the CMTC self diagnosis before
replacing the CMTC module.
REMOVAL
(1) Disconnect and isolate the negative battery
cable.
(2) Remove the overhead console from the headlin-
er.(Refer to 8 - ELECTRICAL/OVERHEAD CON-
SOLE - REMOVAL).
(3) Remove the screws holding Compass Mini-Trip
Computer module in the overhead console (Fig. 5).
(4) Disconnect the CMTC module electrical connec-
tor. Depress the retaining tab and pull straight
apart.
(5) Remove CMTC module from console assembly.
INSTALLATION
(1) Position the compass mini-trip computer mod-
ule in the overhead console.
(2) Install the screws holding the compass mini-
trip computer module in the overhead console.
(3) Connect the module electrical connector.
(4) Install the overhead console on the headlin-
er(Refer to 8 - ELECTRICAL/OVERHEAD CON-
SOLE - INSTALLATION).
(5) Connect the negative battery cable.
(6) Check CMTC module function.
8M - 6 MESSAGE SYSTEMSDR
OVERHEAD CONSOLE (Continued)