engine DODGE RAM 2002 Service Repair Manual

OPERATION
The upshift indicator gives an indication to the
vehicle operator when the transmission should be
shifted to the next highest gear in order to achieve
the best fuel economy. This indicator is controlled by
a transistor on the instrument cluster circuit board
based upon the cluster programming and electronic
messages received by the cluster from the Powertrain
Control Module (PCM) over the Chrysler Collision
Detection (CCD) data bus. The upshift indicator bulb
receives battery current on the instrument cluster
electronic circuit board through the fused ignition
switch output (st-run) circuit whenever the ignition
switch is in the On or Start positions; therefore, the
lamp will always be off when the ignition switch is in
any position except On or Start. The bulb only illu-
minates when it is provided a path to ground by the
instrument cluster transistor. On models not
equipped with a manual transmission, the incandes-
cent bulb and bulb holder unit are not installed at
the factory when the vehicle is built. The instrument
cluster will turn on the upshift indicator for the fol-
lowing reasons:
²Upshift Lamp-On Message- Each time the
cluster receives an upshift lamp-on message from the
PCM indicating the engine speed and load conditions
are right for a transmission upshift to occur, the
upshift indicator is illuminated. The indicator
remains illuminated until the cluster receives an
upshift lamp-off message from the PCM or until the
ignition switch is turned to the Off position, which-
ever occurs first. The PCM 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 indicator will be
turned on during the bulb check portion of the test to
confirm the functionality of the indicator and the
cluster control circuitry.
The PCM continually monitors the engine speed
and load conditions to determine the proper fuel and
ignition requirements. The PCM then sends the
proper messages to the instrument cluster. If the
upshift indicator fails to light during normal vehicle
operation, replace the bulb with a known good unit.
For further diagnosis of the upshift indicator or the
instrument cluster circuitry that controls the indica-
tor, (Refer to 8 - ELECTRICAL/INSTRUMENT
CLUSTER - DIAGNOSIS AND TESTING). For
proper diagnosis of the PCM, the CCD data bus, or
the message inputs to the instrument cluster that
control the upshift indicator, a DRBIIItscan tool isrequired. Refer to the appropriate diagnostic infor-
mation.
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 temperature gauge. The voltage gauge con-
sists 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 8 volts to 18 volts. An International Con-
trol and Display Symbol icon for ªBattery Charging
Conditionº is located directly below the lowest grad-
uation of the gauge scale. The voltage gauge graphics
are white against a black 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 white graph-
ics appear blue-green and the red graphics appear
red. The orange gauge needle is internally illumi-
nated. Gauge illumination is provided by replaceable
incandescent bulb and bulb holder units located on
the instrument cluster electronic circuit board. 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 the cluster programming and elec-
tronic messages received by the cluster from the
Powertrain Control Module (PCM) over the Chrysler
Collision Detection (CCD) data bus. The voltage
gauge is an air core magnetic unit that receives bat-
tery current on the instrument cluster electronic cir-
cuit board through the fused ignition switch output
(st-run) 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:
²Charge Fail Message- Each time the cluster
receives a message from the PCM indicating a charge
fail condition (system voltage is 10.8 volts or lower),
the gauge needle is moved to the 8 volt graduation
on the gauge scale and the check gauges indicator is
illuminated. The gauge needle remains on the 8 volt
BR/BEINSTRUMENT CLUSTER 8J - 33
UPSHIFT INDICATOR (Continued)

graduation and the check gauges indicator remains
illuminated until the cluster receives a message from
the PCM indicating there is no charge fail condition
(system voltage is 10.9 volts or higher, but lower
than 16.7 volts), or until the ignition switch is turned
to the Off position, whichever occurs first. On models
equipped with the optional diesel engine, the instru-
ment cluster is programmed to support the voltmeter
gauge needle above the low end of normal graduation
and suppress the check gauges indicator operation
until ten seconds after the engine intake manifold air
heater has completed its cycle.
²Voltage High Message- Each time the cluster
receives a message from the PCM indicating a volt-
age high condition (system voltage is 16.7 volts or
higher), the gauge needle is moved to the 18 volt
graduation on the gauge scale and the check gauges
indicator is illuminated. The gauge needle remains
on the 18 volt graduation and the check gauges indi-
cator remains illuminated until the cluster receives a
message from the PCM indicating there is no voltage
high condition (system voltage is 16.6 volts or lower,
but higher than 10.9 volts), or until the ignition
switch is turned to the Off position, whichever occurs
first.
²Message Failure- If the cluster fails to receive
a system voltage message, it will hold the gauge nee-
dle at the last indication until a new message is
received, 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 gauge needle will be
swept to several calibration points on the gauge scale
in a prescribed sequence in order to confirm the func-
tionality of the gauge and the cluster control cir-
cuitry.
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 charge fail or voltage high condi-
tion, it may indicate that the charging system
requires service. For proper diagnosis of the charging
system, the CCD data bus, or the message inputs to
the instrument cluster that control the voltage
gauge, a DRBIIItscan tool is required. Refer to the
appropriate diagnostic information.WAIT-TO-START INDICATOR
DESCRIPTION
A wait-to-start indicator is standard equipment on
all instrument clusters, but is only functional in vehi-
cles equipped with an optional diesel engine. The
wait-to-start indicator is located near the lower edge
of the instrument cluster overlay, to the right of cen-
ter. The wait-to-start indicator consists of a stenciled
cutout of the text ªWAIT TO STARTº in the opaque
layer of the cluster overlay. The dark outer layer of
the overlay prevents the indicator from being clearly
visible when it is not illuminated. A red lens located
behind the cutout causes the ªWAIT TO STARTº text
to appear in red through the translucent outer layer
of the overlay when the indicator is illuminated from
behind by a Light Emitting Diode (LED) that is sol-
dered onto the instrument cluster electronic circuit
board. The wait-to-start indicator 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 intake
air heater is energized in its preheat operating mode.
This indicator is controlled by a hard wired input to
the instrument cluster from the Engine Control Mod-
ule (ECM). The wait-to-start indicator Light Emitting
Diode (LED) receives battery current on the instru-
ment cluster electronic circuit board through the
fused ignition switch output (st-run) circuit whenever
the ignition switch is in the On or Start positions;
therefore, the lamp will always be off when the igni-
tion switch is in any position except On or Start. The
indicator LED only illuminates when it is switched to
ground by the input from the ECM. The ECM will
turn on the wait-to-start indicator by pulling the
wait-to-start indicator driver circuit to ground each
time the ignition switch is turned to the On or Start
positions. The indicator then remains illuminated
until the ECM detects that the air within the intake
manifold is the proper temperature to ensure reliable
and efficient engine starting, until the ECM detects
that the engine is running, or until the ignition
switch is turned to the Off position, whichever occurs
first.
The ECM continually monitors the intake manifold
air temperature sensor, the Manifold Absolute Pres-
sure (MAP) sensor, and many other vehicle condi-
tions to determine when the wait-to-start indicator
should be illuminated. For proper diagnosis of the
wait-to-start indicator, the ECM, or the inputs the
ECM uses to control the wait-to-start indicator oper-
ation, a DRBIIItscan tool is required. Refer to the
appropriate diagnostic information.
8J - 34 INSTRUMENT CLUSTERBR/BE
VOLTAGE GAUGE (Continued)

INDICATOR DOES NOT ILLUMINATE WITH WASHER
RESERVOIR EMPTY
(1) Disconnect and isolate the battery negative
cable. Disconnect the headlamp and dash wire har-
ness connector for the washer fluid level switch from
the washer fluid level switch connector receptacle.
Check for continuity between the ground circuit cav-
ity of the headlamp and dash wire harness connector
for the washer fluid level switch and a good ground.
There should be continuity. If OK, go to Step 2. If not
OK, repair the open ground circuit to ground (G100)
as required.
(2) Remove the instrument cluster from the instru-
ment panel. Check for continuity between the washer
fluid switch sense circuit cavities of the headlamp
and dash wire harness connector for the washer fluid
level switch and the instrument panel wire harness
connector (Connector C2) for the instrument cluster.
If OK, replace the faulty washer fluid level switch. If
not OK, repair the open washer fluid switch sense
circuit between the washer fluid level switch and the
instrument cluster as required.
INDICATOR STAYS ILLUMINATED WITH WASHER
RESERVOIR FULL
(1) Disconnect and isolate the battery negative
cable. Disconnect the headlamp and dash wire har-
ness connector for the washer fluid level switch from
the washer fluid level switch connector receptacle.
Check for continuity between the ground circuit ter-
minal and the washer fluid switch sense terminal in
the washer fluid level switch connector receptacle.
There should be no continuity. If OK, go to Step 2. If
not OK, replace the faulty washer fluid level switch.
(2) Remove the instrument cluster from the instru-
ment panel. Check for continuity between the washer
fluid switch sense circuit cavity of the headlamp and
dash wire harness connector for the washer fluid
level switch and a good ground. There should be no
continuity. If not OK, repair the shorted washer fluid
switch sense circuit between the washer fluid level
switch and the instrument cluster as required.
WATER-IN-FUEL INDICATOR
DESCRIPTION
A water-in-fuel indicator is standard equipment on
all instrument clusters, but is only functional in vehi-
cles equipped with an optional diesel engine. The
water-in-fuel indicator is located near the lower edge
of the instrument cluster overlay, to the left of center.
The water-in-fuel indicator consists of a stencilled
cutout of the text ªWATER IN FUELº 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 redlens located behind the cutout causes the ªWATER
IN FUELº text to appear in red through the translu-
cent outer layer of the overlay when the indicator is
illuminated from behind by a Light Emitting Diode
(LED) soldered onto the instrument cluster electronic
circuit board. The water-in-fuel indicator is serviced
as a unit with the instrument cluster.
OPERATION
The water-in-fuel indicator gives an indication to
the vehicle operator when the water accumulated in
the diesel engine fuel filter/separator filter bowl
requires draining. 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 Engine Control
Module (ECM) over the Chrysler Collision Detection
(CCD) data bus. The water-in-fuel indicator Light
Emitting Diode (LED) receives battery current on the
instrument cluster electronic circuit board through
the fused ignition switch output (st-run) circuit
whenever the ignition switch is in the On or Start
positions; therefore, the indicator will always be off
when the ignition switch is in any position except On
or Start. The LED only illuminates when it is
switched to ground by the instrument cluster transis-
tor. 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 indicator is illuminated
for about two seconds as a bulb test.
²Water-In-Fuel Lamp-On Message- Each time
the cluster receives a water-in-fuel lamp-on message
from the ECM, the indicator will be illuminated. The
indicator remains illuminated until the cluster
receives a water-in-fuel lamp-off message from the
ECM 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 indicator will be
turned on during the bulb check portion of the test to
confirm the functionality of the LED and the cluster
control circuitry.
The ECM continually monitors the water-in-fuel
sensor, then sends the proper messages to the instru-
ment cluster. For further diagnosis of the water-in-
fuel indicator or the instrument cluster circuitry that
controls the indicator, (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND TEST-
ING). For proper diagnosis of the water-in-fuel
sensor, the ECM, the CCD data bus, or the message
inputs to the instrument cluster that control the
water-in-fuel indicator, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic
information.
8J - 36 INSTRUMENT CLUSTERBR/BE
WASHER FLUID INDICATOR (Continued)

FOG LAMP
DIAGNOSIS AND TESTING - FOG LAMP
CONDITION POSSIBLE CAUSES CORRECTION
FOG LAMPS ARE DIM
WITH ENGINE IDLING OR
IGNITION TURNED OFF.1. Loose or corroded battery cables. 1. Clean and secure battery cable clamps
and posts.
2. Loose or worn generator drive
belt.2. Adjust or replace generator drive belt.
3. Charging system output too low. 3. Test and repair charging system.
4. Battery has insufficient charge. 4. Test battery state-of -charge.
5. Battery is sulfated or shorted. 5. Load test battery.
6. Poor lighting circuit Z33-ground. 6. Test for voltage drop across Z33-ground
locations.
FOG LAMP BULBS BURN
OUT FREQUENTLY1. Charging system output too high. 1. Test and repair charging system.
2. Loose or corroded terminals or
splices in circuit.2. Inspect and repair all connectors and
splices.
FOG LAMPS ARE DIM
WITH ENGINE RUNNING
ABOVE IDLE1. Charging system output too low. 1. Test and repair charging system.
2. Poor lighting circuit Z33-ground. 2. Test for voltage drop across Z33-ground
locations.
3. High resistance in fog lamp circuit. 3. Test amperage draw of fog lamp circuit.
FOG LAMPS FLASH
RANDOMLY1. Poor lighting circuit Z33-ground. 1. Test for voltage drop across Z33-ground
locations.
2. High resistance in fog lamp circuit. 2. Test amperage draw of fog lamp circuit.
3. Faulty fog lamp switch. 3. Replace fog lamp switch.
4. Loose or corroded terminals or
splices in circuit.4. Inspect and repair all connectors and
splices.
FOG LAMPS DO NOT
ILLUMINATE1. Blown fuse for fog lamp. 1.Trace short and replace fuse.
2. No Z33-ground at fog lamps. 2. Repair circuit ground.
3. Faulty fog lamp switch. 3. Replace fog lamp switch.
4. Broken connector terminal or wire
splice in fog lamp circuit.4. Repair connector terminal or wire splice.
5. Defective or burned out bulb. 5. Replace bulb.
FOG LAMPS ARE
INOPERATIVE AND FOG
LAMP INDICATOR LIGHT
ALWAYS STAYS ON.1. Fog lamp/DRL* feed shorted to
ground.1. Check wiring circuit from fog lamp/DRL*
fuse to fog lamp. Trace short circuit in
wiring and repair.
FOG LAMPS ARE
INOPERATIVE AND FOG
LAMP INDICATOR LIGHT
IS ILLUMINATED.1. Fog lamp/DRL* fuse defective. 1. Trace short circuit and replace fuse.
2. Open circuit from fog lamp fuse to
fog lamp.2. Check wiring circuit from fog lamp/DRL*
fuse to fog lamp. Trace open circuit in
wiring and repair.
8L - 10 LAMPS/LIGHTING - EXTERIORBR/BE

DIAGNOSIS AND TESTING - HEADLAMP
A good ground is necessary for proper lighting
operation. Grounding is provided by the lamp socket
when it comes in contact with the metal body, or
through a separate ground wire.
Always begin any diagnosis by testing all of the
fuses and circuit breakers in the system. For com-plete circuit diagrams, refer to the appropriate wir-
ing information. The wiring information includes
wiring diagrams, proper wire and connector repair
procedures, details of wire harness routing and
retention, connector pin-out information and location
views for the various wire harness connectors, splices
and grounds.
CONDITION POSSIBLE CAUSES CORRECTION
HEADLAMPS ARE DIM
WITH ENGINE IDLING1. Loose or corroded battery cables. 1. Clean and secure battery cable clamps
and posts.
OR IGNITION TURNED
OFF2. Loose or worn generator drive
belt.2. Adjust or replace generator drive belt.
3. Charging system output too low. 3. Test and repair charging system.
4. Battery has insufficient charge. 4. Test battery state-of -charge.
5. Battery is sulfated or shorted. 5. Load test battery.
6. Poor lighting circuit Z3-ground. 6. Test for voltage drop across Z3-ground
locations.
7. Both headlamp bulbs defective. 7. Replace both headlamp bulbs.
HEADLAMP BULBS BURN
OUT1. Charging system output too high. 1. Test and repair charging system.
FREQUENTLY 2. Loose or corroded terminals or
splices in circuit.2. Inspect and repair all connectors and
splices.
HEADLAMPS ARE DIM
WITH ENGINE RUNNING1. Charging system output too low. 1. Test and repair charging system.
ABOVE IDLE* 2. Poor lighting circuit Z3-ground. 2. Test for voltage drop across Z3-ground
locations.
3. High resistance in headlamp
circuit.3. Test amperage draw of headlamp circuit.
4. Both headlamp bulbs defective. 4. Replace both headlamp bulbs.
HEADLAMPS FLASH
RANDOMLY1. Poor lighting circuit Z3-ground. 1. Test for voltage drop across Z3-ground
locations.
2. High resistance in headlamp
circuit.2. Test amperage draw of headlamp circuit.
Should not exceed 30 amps.
3. Faulty headlamps switch circuit
breaker.3. Replace headlamp switch.
4. Loose or corroded terminals or
splices in circuit.4. Inspect and repair all connectors and
splices.
HEADLAMPS (HIGH &
LOW) DO NOT
ILLUMINATE1. No voltage at either headlamp. 1. Voltage should always be present. Trace
short circuit and replace BOTH headlamp
fuses. Check wiring circuit from Right
headlamp fuse to headlamp. (Repeat for
Left side)
8L - 14 LAMPS/LIGHTING - EXTERIORBR/BE
HEADLAMP (Continued)

HEADLAMP RELAY
DESCRIPTION
The headlamp (or security) relay is located in the
Power Distribution Center (PDC) near the battery in
the engine compartment (Fig. 14). See the fuse and
relay layout label affixed to the inside surface of the
PDC cover for headlamp relay identification and loca-
tion. The headlamp relay is a conventional Interna-
tional Standards Organization (ISO) micro relay.
Relays conforming to the ISO specifications have
common physical dimensions, current capacities, ter-
minal patterns, and terminal functions. The relay is
contained within a small, rectangular, molded plastic
housing. The relay is connected to all of the required
inputs and outputs through its PDC receptacle by
five male spade-type terminals that extend from the
bottom of the relay base. The ISO designation for
each terminal is molded into the base adjacent to the
terminal. The ISO terminal designations are as fol-
lows:
²30 (Common Feed)- This terminal is con-
nected to the movable contact point of the relay.
²85 (Coil Ground)- This terminal is connected
to the ground feed side of the relay control coil.
²86 (Coil Battery)- This terminal is connected
to the battery feed side of the relay control coil.
²87 (Normally Open)- This terminal is con-
nected to the normally open fixed contact point of the
relay.
²87A (Normally Closed)- This terminal is con-
nected to the normally closed fixed contact point of
the relay.
The headlamp relay cannot be adjusted or
repaired. If the relay is damaged or faulty, it must be
replaced.
OPERATION
The headlamp (or security) relay is an electrome-
chanical switch that uses a low current input from
the high-line or premium Central Timer Module
(CTM) to control a high current output to the head-
lamps. The movable common feed contact point is
held against the fixed normally closed contact point
by spring pressure. When the relay coil is energized,
an electromagnetic field is produced by the coil wind-
ings. This electromagnetic field draws the movable
relay contact point away from the fixed normally
closed contact point, and holds it against the fixed
normally open contact point. When the relay coil is
de-energized, spring pressure returns the movable
contact point back against the fixed normally closed
contact point. A resistor or diode is connected in par-
allel with the relay coil in the relay, and helps to dis-
sipate voltage spikes and electromagnetic
interference that can be generated as the electromag-
netic field of the relay coil collapses.
The headlamp relay terminals are connected to the
vehicle electrical system through a connector recepta-
cle in the Power Distribution Center (PDC). The
inputs and outputs of the headlamp relay include:
²The common feed terminal (30) is connected to
ground at all times through a take out and eyelet
terminal connector of the right headlamp and dash
wire harness that is secured by a ground screw to
the left fender inner shield near the PDC in the
engine compartment.
²The coil ground terminal (85) is connected to the
Central Timer Module (CTM) through the security
relay control circuit. The CTM energizes the head-
lamp relay control coil by internally pulling this cir-
cuit to ground.
²The coil battery terminal (86) is connected to
battery current at all times through a fused B(+) cir-
cuit that is internal to the PDC.
²The normally open terminal (87) is connected to
the headlamps at all times through the beam select
switch low beam output circuit. This circuit provides
a path to ground for the headlamps through the com-
mon feed terminal when the headlamp relay control
coil is energized by the CTM.
²The normally closed terminal (87A) is not con-
nected to any circuit in this application, but is
grounded through the common feed terminal when
the headlamp relay control coil is de-energized.
The headlamp relay can be diagnosed using con-
ventional diagnostic tools and methods.
DIAGNOSIS AND TESTING - HEADLAMP RELAY
The headlamp (or security) relay (Fig. 15) is
located in the Power Distribution Center (PDC) near
the battery in the engine compartment. See the fuse
and relay layout label affixed to the inside surface of
Fig. 14 Power Distribution Center
1 - COVER
2 - POWER DISTRIBUTION CENTER
BR/BELAMPS/LIGHTING - EXTERIOR 8L - 17

LAMPS/LIGHTING - INTERIOR
TABLE OF CONTENTS
page page
LAMPS/LIGHTING - INTERIOR
SPECIFICATIONS
INTERIOR LAMPS.....................33
DOME LAMP
REMOVAL.............................34
INSTALLATION.........................34
DOOR AJAR SWITCH
DESCRIPTION.........................34
DIAGNOSIS AND TESTING - DOOR AJAR
SWITCH............................34
REMOVAL.............................35
INSTALLATION.........................35GLOVE BOX LAMP AND SWITCH
REMOVAL.............................35
INSTALLATION.........................36
READING LAMP
DESCRIPTION.........................36
OPERATION...........................36
REMOVAL.............................36
INSTALLATION.........................37
VANITY LAMP
REMOVAL.............................37
INSTALLATION.........................37
LAMPS/LIGHTING - INTERIOR
SPECIFICATIONS
INTERIOR LAMPS
LAMP BULB
A/C HEATER CONTROL 158
ASH RECEIVER 161
CIGAR LIGHTER 161
HEADLAMP SWITCH 158
HEATER CONTROL 158
INSTRUMENT CLUSTER PC194
RADIO ASC
AIRBAG HIGH LINE PC194
AIRBAG LOW LINE PC74
ANTI-LOCK BRAKE PC74
BATTERY VOLTAGE PC194
BRAKE WARNING PC194LAMP BULB
CHECK ENGINE PC74
ENGINE OIL PRESSURE PC74
FOUR WHEEL DRIVE PC194
HIGH BEAM PC194
LOW FUEL PC194
LOW WASHER FLUID PC74
MAINTENANCE
REQUIREDPC74
MESSAGE CENTER PC194
SEAT BELT PC74
TURN SIGNAL PC194
UPSHIFT PC74
DOME 1004
GLOVE COMPARTMENT 1891
VANITY MIRROR LAMP P/N 6501966
BR/BELAMPS/LIGHTING - INTERIOR 8L - 33

using the U.S./Metric push button. The displayed
temperature is not an instant reading of conditions,
but an average temperature. It may take the ther-
mometer display several minutes to respond to a
major temperature change, such as driving 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 thermometer unit memory. When the ignition
switch is turned to the On position again, the ther-
mometer will display the memory temperature if the
engine coolant temperature is above about 43É C
(109É F). If the engine coolant temperature is below
about 43É C (109É F), the thermometer will display
the actual temperature sensed by the ambient tem-
perature sensor. The thermometer temperature dis-
play update interval varies with the vehicle speed;
therefore, if the temperature reading seems inaccu-
rate, drive the vehicle for at least three minutes
while maintaining a speed of 48 kilometers-per-hour
(30 miles-per-hour) or higher.
The thermometer function is supported by an
ambient temperature sensor. The sensor is mounted
outside the passenger compartment near the front
and center of the vehicle, and is hard wired to the
module. The ambient temperature sensor is available
as a separate service item.
STANDARD PROCEDURE
STANDARD PROCEDURE - COMPASS
CALIBRATION
CAUTION: Do not place any external magnets, such
as magnetic roof mount antennas, in the vicinity of
the compass. Do not use magnetic tools when ser-
vicing the overhead console.
The electronic compass unit features a self-cali-
brating design, which simplifies the calibration pro-
cedure. This feature automatically updates the
compass calibration while the vehicle is being driven.
This allows the compass unit to compensate for small
changes in the residual magnetism that the vehicle
may acquire during normal use. If the compass read-
ings appear to be erratic or out of calibration, per-
form the following calibration procedure. Also, new
service replacement compass mini-trip computer
modules must have their compass calibrated using
this procedure. Do not attempt to calibrate the com-
pass near large metal objects such as other vehicles,
large buildings, or bridges; or, near overhead or
underground power lines.
(1) Start the engine. If the compass/temperature
data is not currently being displayed, momentarily
depress and release the Step push button to stepthrough the display options until you have reached
the compass/temperature display.
(2) Depress both the U.S./Metric and the Step
push buttons at the same time for more than six sec-
onds, until ªCALº appears in the display, then release
both push buttons. The ªCALº in the display indi-
cates that the compass is in the calibration mode.
(3) Drive the vehicle on a level surface, at least
fifty feet away from large metal objects and power
lines, in all four compass directions, such as driving
around a city block several times or driving in two to
three complete circles at a slow to medium speed.
(4) When the calibration is successfully completed,
ªCALº will disappear from the display and normal
compass mini-trip computer operation will resume.
NOTE: If the ªCALº message remains in the display,
either there is excessive magnetism near the com-
pass, or the unit is faulty. Repeat the calibration
procedure at least one more time.
NOTE: If the wrong direction is still indicated in the
compass display, the area selected for calibration
may be too close to a strong magnetic field. Repeat
the calibration procedure in another location.
STANDARD PROCEDURE - COMPASS
VARIATION ADJUSTMENT
Compass variance, also known as magnetic decli-
nation, is the difference in angle between magnetic
north and true geographic north. In some geographic
locations, the difference between magnetic and geo-
graphic north is great enough to cause the compass
to give false readings. If this problem occurs, the
compass variance must be set. There are two meth-
ods that can be used to enter this information into
the compass mini-trip computer module. They are
the zone method and the direct method.
ZONE METHOD
(1) Using the Variance Settings map, find your
geographic location and note the zone number (Fig.
2).
(2) Turn the ignition switch to the On position. If
the compass/temperature data is not currently being
displayed, momentarily depress and release the Step
push button to step through the display options until
you have reached the compass/temperature display.
(3) Depress both the U.S./Metric and the Step
push buttons at the same time and hold them down
for more than 100 milliseconds, but not more than
one second. The compass mini-trip computer will
enter the variation adjustment mode and ªVARº
along with the current variance zone will appear in
the display.
8M - 4 MESSAGE SYSTEMSBR/BE
OVERHEAD CONSOLE (Continued)

AMBIENT TEMP SENSOR
DESCRIPTION
Ambient air temperature is monitored by the com-
pass mini-trip computer module through the ambient
temperature sensor. The ambient temperature sensor
is a variable resistor mounted to a bracket that is
secured with a screw to the underside of the hood
panel near the hood latch striker in the engine com-
partment (Fig. 8).
For complete circuit diagrams, refer toOverhead
Consolein the Contents of Wiring Diagrams. The
ambient temperature sensor cannot be adjusted or
repaired and, if faulty or damaged, it must be
replaced.
OPERATION
The ambient temperature sensor is a variable
resistor that operates on a five-volt reference signal
sent to it by the compass mini-trip computer module.
The resistance in the sensor changes as temperature
changes, changing the return circuit voltage to the
compass mini-trip computer module. Based upon the
resistance in the sensor, the compass mini-trip com-
puter module senses a specific voltage on the return
circuit, which it is programmed to correspond to a
specific temperature.
DIAGNOSIS AND TESTING - AMBIENT
TEMPERATURE SENSOR
The thermometer function is supported by the
ambient temperature sensor, a wiring circuit, and a
portion of the compass mini-trip computer module. If
any portion of the ambient temperature sensor cir-
cuit fails, the compass/thermometer display function
will self-diagnose the circuit. If 55É C (131É F)
appears in the display, the sensor is being exposed to
temperatures above 55É C (131É F), or the sensor cir-
cuit is shorted. If ±40É C (±40É F) appears in the dis-
play, the sensor is being exposed to temperatures
below ±40É C (±40É F), or the sensor circuit is open.
The ambient temperature sensor circuit can also be
diagnosed using the following Sensor Test, and Sen-
sor Circuit Test. If the temperature sensor and cir-
cuit are confirmed to be OK, but the temperature
display is inoperative or incorrect, refer toDiagnosis
and Testing the Compass Mini-Trip Computer.
For complete circuit diagrams, refer toWiring Dia-
grams.
SENSOR TEST
(1) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the ambient temperature sensor wire har-
ness connector.(2) Measure the resistance of the ambient temper-
ature sensor. At ±40É C (±40É F), the sensor resis-
tance is 336 kilohms. At 55É C (131É F), the sensor
resistance is 2.488 kilohms. The sensor resistance
should read between these two values. If OK, refer to
theSensor Circuit Test below. If not OK, replace
the faulty ambient temperature sensor.
SENSOR CIRCUIT TEST
(1) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the ambient temperature sensor wire har-
ness connector and the overhead console wire har-
ness connector.
(2) Connect a jumper wire between the two termi-
nals in the body half of the ambient temperature sen-
sor wire harness connector.
(3) Check for continuity between the sensor return
circuit and the ambient temperature sensor signal
circuit cavities of the roof wire harness overhead con-
sole connector. There should be continuity. If OK, go
to Step 4. If not OK, repair the open sensor return
circuit or ambient temperature sensor signal circuit
to the ambient temperature sensor as required.
(4) Remove the jumper wire from the body half of
the ambient temperature sensor wire harness con-
nector. Check for continuity between the sensor
return circuit cavity of the roof wire harness over-
head console connector and a good ground. There
should be no continuity. If OK, go to Step 5. If not
OK, repair the shorted sensor return circuit as
required.
(5) Check for continuity between the ambient tem-
perature sensor signal circuit cavity of the roof wire
harness overhead console connector and a good
ground. There should be no continuity. If OK, refer to
Diagnosis and Testing the Compass Mini-Trip
Computerin this section. If not OK, repair the
shorted ambient temperature sensor signal circuit as
required.
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Locate the ambient temperature sensor, on the
underside of the hood near the hood latch striker
(Fig. 8).
(3) Disconnect the wire harness connector from the
ambient temperature sensor connector receptacle.
(4) Remove the one screw that secures the ambient
temperature sensor bracket to the inner hood rein-
forcement.
(5) Remove the ambient temperature sensor from
the inner hood reinforcement.
8M - 12 MESSAGE SYSTEMSBR/BE

fault or malfunction. Refer to the appropriate diag-
nostic information to diagnose the problem.
SPECIAL TOOLS - AIRBAG SYSTEM
AIRBAG CONTROL MODULE
DESCRIPTION
The Airbag Control Module (ACM) is concealed
underneath the plastic ACM trim cover (automatic
transmission) or center console (manual transmis-
sion), directly below the instrument panel in the pas-
senger compartment of the vehicle. The ACM is
secured with screws to a stamped steel mounting
bracket located under the instrument panel center
support bracket on the floor panel transmission tun-
nel. The ACM contains an electronic microprocessor,
an electronic impact sensor, an electromechanical saf-
ing sensor, and an energy storage capacitor. TheACM is connected to the vehicle electrical system
through a take out and connector of the instrument
panel wire harness.
The ACM cannot be repaired or adjusted and, if
damaged or faulty, it must be replaced.
OPERATION
The microprocessor in the ACM contains the airbag
system logic circuits, and it monitors and controls all
of the airbag system components. The ACM also uses
On-Board Diagnostics (OBD) and can communicate
with other electronic modules in the vehicle as well
as with the DRBIIItscan tool using the Chrysler
Collision Detection (CCD) data bus network. This
method of communication is used for control of the
airbag indicator in the ElectroMechanical Instrument
Cluster (EMIC) and for airbag system diagnosis and
testing through the 16-way data link connector
located on the lower left edge of the instrument
panel. (Refer to 8 - ELECTRICAL/ELECTRONIC
CONTROL MODULES/COMMUNICATION - OPER-
ATION). The ACM microprocessor continuously mon-
itors all of the airbag system electrical circuits to
determine the system readiness. If the ACM detects
a monitored system fault, it sets an active Diagnostic
Trouble Code (DTC) and sends messages to the
EMIC over the CCD data bus to turn on the airbag
indicator. (Refer to 8 - ELECTRICAL/INSTRUMENT
CLUSTER/AIRBAG INDICATOR - OPERATION). If
the airbag system fault is still present when the igni-
tion switch is turned to the Off position, the DTC is
stored in memory by the ACM. However, if a fault
does not recur for a number of ignition cycles, the
ACM will automatically erase the stored DTC.
The ACM receives battery current through two cir-
cuits, on a fused ignition switch output (run) circuit
through a fuse in the Junction Block (JB), and on a
fused ignition switch output (start-run) circuit
through a second fuse in the JB. The ACM is
grounded through a ground circuit and take out of
the instrument panel wire harness. This take out has
a single eyelet terminal connector secured by a nut to
a ground stud located on the forward extension of the
left front fender wheel housing in the engine com-
partment. Therefore, the ACM is operational when-
ever the ignition switch is in the Start or On
positions. The ACM also contains an energy-storage
capacitor. When the ignition switch is in the Start or
On positions, this capacitor is continually being
charged with enough electrical energy to deploy the
airbags for up to one second following a battery dis-
connect or failure. The purpose of the capacitor is to
provide backup airbag system protection in case
there is a loss of battery current supply to the ACM
during an impact. The capacitor is only serviced as a
unit with the ACM.
Fig. 4 16-Way Data Link Connector - Typical
1 - 16±WAY DATA LINK CONNECTOR
2 - BOTTOM OF INSTRUMENT PANEL
Puller C-3428-B
8O - 6 RESTRAINTSBR/BE
RESTRAINTS (Continued)