2002 DODGE RAM length

BUS MESSAGE CODING
The first part of a data bus message has an Iden-
tification (ID) byte. The ID byte contains message
priority, message identification, message content and
message length information. All messages sent over
the data bus are coded for both priority and identifi-
cation.
PRIORITY
Messages can be broadcast almost simultaneously
by modules over the CCD data bus. Therefore, all
messages are defined and ranked by a predetermined
priority. When two CCD chips start a message at
exactly the same time, non-destructive arbitration
occurs between the two CCD chips. Arbitration will
occur based upon the priority code, to determine
which message takes priority on the data bus and to
prevent data collision. If a CCD chip senses a mes-
sage of higher priority being transmitted, it stops
transmitting its message. The higher priority mes-
sage is then transmitted in its entirety without inter-ruption. The other CCD chips on the data bus do not
allow any other messages to be broadcast.
To determine the winner in an arbitration, all mes-
sages start with an ID byte which contains the pre-
determined priority code. In the digital broadcast,
zero is the dominant bit. All ID bytes start with a
zero. This is the start of the message. With zeros
being the dominant bit, messages starting with more
zeros have a higher priority. For example: of the two
messages below, Message #2 loses arbitration at the
second bit, where Message #1 has a zero and Mes-
sage #2 has a one (Fig. 9). After the message is
broadcast, an idle period occurs while all micropro-
cessors can queue, if necessary, and attempt to
broadcast their messages again.
²Message #1 = 00010110
²Message #2 = 01010101
Fig. 7 Bus Termination
BR/BEELECTRONIC CONTROL MODULES 8E - 9
COMMUNICATION (Continued)

MESSAGE IDENTIFICATION
Because messages are broadcast over the data bus,
all modules can receive them, yet not all modules
need all messages. In order to enhance microproces-
sor speed, unneeded messages are filtered out. The
ID byte, along with showing message priority, alsoidentifies the data, content and length. The electronic
control module, through its CCD chip transceiver,
monitors the ID code of the messages. If the message
is not for that particular module, the message is sim-
ply ignored. Once the module recognizes a message
that it requires, the rest of the message is monitored
and processed.
TRANSMISSION VERIFICATION
Once a CCD chip transmits a message over the
CCD data bus, the message is received by the trans-
mitting module at the same time through the CCD
chip differential transceiver. The module knows the
message was broadcast correctly when it receives its
own message back. If the message received does not
match the message transmitted, the message is said
to be corrupt.
Corruption occurs when the message is incorrectly
transmitted on the data bus. Corruption can also
occur from interference, wiring problems, or other
data bus problems. In the case of a corrupt message,
the module attempts to have the CCD chip re-send
the message.
Fig. 8 Voltage Cycling to Correspond to Message
Fig. 9 Message Arbitration
8E - 10 ELECTRONIC CONTROL MODULESBR/BE
COMMUNICATION (Continued)

harness connector for the heated mirror switch. If
OK, go to Step 5. If not OK, repair the open fused
ignition switch output (run/start) circuit to the fuse
in the JB as required.
(5) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Reconnect the 3-way instrument panel wire harness
connector for the heated mirror switch to the heated
mirror switch connector receptacle on the back of the
a/c heater control. Reconnect the battery negative
cable. Turn the ignition switch to the On position.
Depress and release the heated mirror switch. The
amber heated mirror system indicator lamp next to
the heated mirror switch button should light. If OK,
go to Step 6. If not OK, replace the faulty a/c heater
control.
(6) Back probe the fused heated mirror relay out-
put circuit cavity of the 3-way instrument panel wire
harness connector for the heated mirror switch on
the back of the a/c heater control and check for volt-
age (battery voltage less the resistance in both out-
side mirror heating grids). If OK, (Refer to 8 -
ELECTRICAL/HEATED MIRRORS/HEATED MIR-
ROR GRID - DIAGNOSIS AND TESTING).
HEATED MIRROR GRID
DESCRIPTION
Vehicles equipped with the optional heated mirror
system have an electrically operated heating grid
located behind the mirror glass of each power oper-
ated outside rear view mirror. The outside mirror
heating grid consists of two thin laminations of plas-
tic that approximate the outer dimensions and shape
of the mirror glass. A single length of resistor wire
weaves in a back and forth pattern between, and is
held in place by the two thin laminations of plastic.
The two ends of the resistor wire terminate near the
inboard edge of the grid, where they are soldered to
the ground feed and battery current feed wires con-
tained in the power mirror wire harness. The heating
grid is then sandwiched between the back of the
molded plastic mirror glass case and the mirror
glass, where it remains in direct contact with the
back of the mirror glass at all times.
The outside mirror heating grids cannot be
repaired and, if faulty or damaged, the entire outside
power mirror unit must be replaced. Refer to Power
Mirrors for the service procedures.
OPERATION
One end of the outside mirror heating grid resistor
wire is connected to a ground feed at all times
through a body ground screw located inside the left
rear corner of the truck cab. Battery current is
directed to the other end of the outside mirror heat-
ing grid resistor wire by the energized heated mirror
relay when the heated mirror switch is in the On
position. As electrical current passes through the
heating grid, the resistance of the wire in the heating
grid converts some of that electrical current into
heat. The heat produced by the heating grid is then
conducted through the back of the mirror glass to
help keep the glass clear of ice, snow or fog.
DIAGNOSIS AND TESTING - HEATED MIRROR
GRID
For circuit descriptions and diagrams (Refer to
Appropriate Wiring Information).
(1) Disconnect and isolate the battery negative
cable. Disconnect the door wire harness connector
from the power mirror wire harness connector at the
power mirror with the inoperative heating grid.
Check for continuity between the ground circuit cav-
ity in the door wire harness connector for the power
mirror and a good ground. If OK, go to Step 2. If not
OK, repair the open ground circuit to ground as
required.
(2) Reconnect the battery negative cable. Turn the
ignition switch to the On position. Turn on the
heated mirror system. Check for voltage (battery
voltage less the resistance in the outside mirror heat-
ing grid that is still connected) at the fused heated
mirror relay output circuit cavity in the door wire
harness connector for the power mirror. If OK, go to
Step 3. If not OK, repair the open fused heated mir-
ror relay output circuit to the heater and air condi-
tioner control unit as required.
(3) Check the outside mirror heating grid by test-
ing for continuity between the ground circuit and the
fused heated mirror relay output circuit cavities in
the power mirror wire harness connector. There
should be continuity. If not OK, replace the faulty
power mirror. If OK, check the resistance through
the outside mirror heating grid. The correct resis-
tance should be from 10 to 16 ohms when measured
at an ambient temperature of 21É C (70É F). If not
OK, replace the faulty power mirror.
8G - 4 HEATED MIRRORSBR/BE
MIRROR SWITCH (Continued)

(6) From the back of the heated seat switch bezel,
gently push the heated seat switch out through the
front of the bezel.
INSTALLATION
Both heated seat switches and the heated seat
switch bezel are available individually for service
replacement.
NOTE: When installing the heated seat switches, be
certain they are installed in the proper mounting
holes of the heated seat switch bezel. Note that the
driver side and passenger side switches are identi-
cal in appearance except for the keyway in the con-
nector receptacle on the backs of the switches. The
driver side switch has the keyway located near the
bottom of the connector receptacle and should be
installed in the left mounting hole of the heated
seat switch bezel. The passenger side switch has
the keyway located near the top of the connector
receptacle and should be installed in the right
mounting hole of the heated seat switch bezel.
(1) From the front of the heated seat switch bezel,
align the back of the heated seat switch with the
proper mounting hole in the heated seat switch bezel
and gently push the switch into the bezel until it
snaps into place.
(2) Position the heated seat switch bezel and both
switches to the instrument panel as a unit.
(3) Reconnect the two instrument panel wire har-
ness connectors to the connector receptacles on the
backs of the heated seat switches.(4) Position the heated seat switch bezel and both
switches in the instrument panel mounting hole as a
unit.
(5) Install and tighten the three screws that secure
the heated seat switch bezel to the instrument panel.
Tighten the screws to 2.2 N´m (20 in. lbs.).
(6) Install the cluster bezel onto the instrument
panel. Refer toCluster Bezelin the index of this
service manual for the location of the proper cluster
bezel installation procedures.
(7) Reconnect the battery negative cable.
HEATED SEAT ELEMENT
DESCRIPTION
Vehicles equipped with the optional heated seat
system have two sets of electrically operated heating
element grids located in each front seat, one set for
the seat cushion and the other set for the seat back.
Each of the heated seat element grids consists of a
single length of resistor wire that is routed in a zig-
zag pattern and captured between a covering and the
adhesive foam rubber backing. Short pigtail wires
with connectors (Fig. 5) are soldered to each end of
each resistor wire element grid, which connect all of
the element grids for each seating position to each
other in series with the heated seat module through
the seat wire harness.
Fig. 4 Heated Seat Switch and Bezel Remove/Install
1 - INSTRUMENT PANEL
2 - SCREW (3)
3 - HEATED SEAT SWITCHES AND BEZEL UNIT
Fig. 5 HEATING ELEMENT INSTALLED
1 - SEAT BACK WIRE HARNESS
2 - HEATED SEAT WIRE HARNESS CONNECTOR
3 - HEATED SEAT CUSHION ELEMENT
8G - 10 HEATED SEAT SYSTEMBR/BE
DRIVER SEAT HEATER SWITCH (Continued)

cause of oil entry into that particular combustion
chamber.
ELECTRODE GAP BRIDGING
Electrode gap bridging may be traced to loose
deposits in the combustion chamber. These deposits
accumulate on the spark plugs during continuous
stop-and-go driving. When the engine is suddenly
subjected to a high torque load, deposits partially liq-
uefy and bridge the gap between electrodes (Fig. 30).
This short circuits the electrodes. Spark plugs with
electrode gap bridging can be cleaned using standard
procedures.
SCAVENGER DEPOSITS
Fuel scavenger deposits may be either white or yel-
low (Fig. 31). They may appear to be harmful, but
this is a normal condition caused by chemical addi-
tives in certain fuels. These additives are designed to
change the chemical nature of deposits and decrease
spark plug misfire tendencies. Notice that accumula-
tion on the ground electrode and shell area may be
heavy, but the deposits are easily removed. Spark
plugs with scavenger deposits can be considered nor-
mal in condition and can be cleaned using standard
procedures.
CHIPPED ELECTRODE INSULATOR
A chipped electrode insulator usually results from
bending the center electrode while adjusting the
spark plug electrode gap. Under certain conditions,
severe detonation can also separate the insulator
from the center electrode (Fig. 32). Spark plugs with
this condition must be replaced.
PREIGNITION DAMAGE
Preignition damage is usually caused by excessive
combustion chamber temperature. The center elec-
trode dissolves first and the ground electrode dis-
solves somewhat latter (Fig. 33). Insulators appear
relatively deposit free. Determine if the spark plug
has the correct heat range rating for the engine.
Determine if ignition timing is over advanced or if
other operating conditions are causing engine over-
heating. (The heat range rating refers to the operat-
ing temperature of a particular type spark plug.
Spark plugs are designed to operate within specific
temperature ranges. This depends upon the thick-
ness and length of the center electrodes porcelain
insulator.)
Fig. 29 Oil or Ash Encrusted
Fig. 30 Electrode Gap Bridging
1 - GROUND ELECTRODE
2 - DEPOSITS
3 - CENTER ELECTRODE
Fig. 31 Scavenger Deposits
1 - GROUND ELECTRODE COVERED WITH WHITE OR
YELLOW DEPOSITS
2 - CENTER ELECTRODE
8I - 18 IGNITION CONTROLBR/BE
SPARK PLUG (Continued)

CAUTION: Do not leave any one spark plug cable
disconnected for longer than necessary during test-
ing. This may cause possible heat damage to the
catalytic converter. Total test time must not exceed
ten minutes.
With the engine running, remove spark plug cable
from spark plug (one at a time) and hold next to a
good engine ground. If the cable and spark plug are
in good condition, the engine rpm should drop and
the engine will run poorly. If engine rpm does not
drop, the cable and/or spark plug may not be operat-
ing properly and should be replaced. Also check
engine cylinder compression.
With the engine not running, connect one end of a
test probe to a good ground. Start the engine and run
the other end of the test probe along the entire
length of all spark plug cables. If cables are cracked
or punctured, there will be a noticeable spark jump
from the damaged area to the test probe. The cable
running from the ignition coil to the distributor cap
can be checked in the same manner. Cracked, dam-
aged or faulty cables should be replaced with resis-
tance type cable. This can be identified by the words
ELECTRONIC SUPPRESSION printed on the cable
jacket.
Use an ohmmeter to test for open circuits, exces-
sive resistance or loose terminals. If equipped,
remove the distributor cap from the distributor.Do
not remove cables from cap.Remove cable from
spark plug. Connect ohmmeter to spark plug termi-
nal end of cable and to corresponding electrode in
distributor cap. Resistance should be 250 to 1000
Ohms per inch of cable. If not, remove cable from dis-
tributor cap tower and connect ohmmeter to the ter-
minal ends of cable. If resistance is not within
specifications as found in the SPARK PLUG CABLE
RESISTANCE chart, replace the cable. Test all spark
plug cables in this manner.
SPARK PLUG CABLE RESISTANCE
MINIMUM MAXIMUM
250 Ohms Per Inch 1000 Ohms Per Inch
3000 Ohms Per Foot 12,000 Ohms Per Foot
To test ignition coil-to-distributor cap cable, do not
remove the cable from the cap. Connect ohmmeter to
rotor button (center contact) of distributor cap and
terminal at ignition coil end of cable. If resistance is
not within specifications as found in the Spark Plug
Cable Resistance chart, remove the cable from the
distributor cap. Connect the ohmmeter to the termi-
nal ends of the cable. If resistance is not within spec-
ifications as found in the Spark Plug CableResistance chart, replace the cable. Inspect the igni-
tion coil tower for cracks, burns or corrosion.
REMOVAL
CAUTION: When disconnecting a high voltage cable
from a spark plug or from the distributor cap, twist
the rubber boot slightly (1/2 turn) to break it loose
(Fig. 37). Grasp the boot (not the cable) and pull it
off with a steady, even force.
INSTALLATION
Install cables into the proper engine cylinder firing
order (Fig. 38) or (Fig. 39).
Fig. 37 Cable Removal
1 - SPARK PLUG CABLE AND BOOT
2 - SPARK PLUG BOOT PULLER
3 - TWIST AND PULL
4 - SPARK PLUG
Fig. 38 Engine Firing OrderÐ5.9L V-8 Engines
BR/BEIGNITION CONTROL 8I - 21
SPARK PLUG CABLE (Continued)

instrument cluster housing with two screws. A face
plate on the indicator housing is visible through a
rectangular cutout in the lower right corner of the
instrument cluster overlay, just below the fuel gauge.
Vehicles with a manual transmission have a block-off
plate mounted to the back of the instrument cluster
behind this cutout in the overlay, in place of the gear
selector indicator. Near the top of this face plate the
following characters are imprinted from left to right:
ªP,º ªR,º ªN,º ªD,º ª2,º and ª1.º Respectively, these
characters represent the park, reverse, neutral,
drive, second gear, and first gear positions of the
transmission gear selector lever on the steering col-
umn. Directly below each character on the face plate
is a small, rectangular window, and behind these
windows is a single, movable red pointer.
The gear selector indicator graphics are white
against a black field except for the single red pointer,
making them clearly visible within the instrument
cluster in daylight. When illuminated from behind by
the panel lamps dimmer controlled cluster illumina-
tion lighting with the exterior lamps turned On, the
white graphics appear blue-green, while the red
pointer still appears red. Indicator illumination is
provided by replaceable incandescent bulb and bulb
holder units located on the instrument cluster elec-
tronic circuit board. The gear selector indicator is
available for service replacement separate from the
instrument cluster. The instrument cluster must be
removed from the instrument panel for service access
to the gear selector indicator. (Refer to 8 - ELECTRI-
CAL/INSTRUMENT CLUSTER - REMOVAL).
OPERATION
The mechanical gear selector indicator gives an
indication of the transmission gear that has been
selected with the automatic transmission gear selec-
tor lever. A red pointer appears in a window below
the character in the indicator representing the trans-
mission gear that has been selected. The small,
spring-loaded pointer moves on a track through a
trolley-like mechanism within the indicator housing.
A short length of small diameter stranded cable is
attached to one side of the pointer trolley and is
encased in a tubular plastic housing that exits the
right side of the indicator. The cable is routed
through the instrument panel and under the steering
column to the left side of the column. The looped end
of the cable is hooked over the end of the PRNDL
driver lever on the steering column gearshift mecha-
nism, and the cable housing is secured in a molded
plastic adjuster and bracket on the column housing.
When the gear selector lever is moved the PRNDL
driver lever moves, which moves the pointer through
the mechanical actuator cable. The cable adjuster
and bracket unit mounted on the steering columnhousing provides a mechanical means of calibrating
the gear selector indicator mechanism. (Refer to 19 -
STEERING/COLUMN - INSTALLATION).
HIGH BEAM INDICATOR
DESCRIPTION
A high beam indicator is standard equipment on
all instrument clusters. The high beam indicator is
located near the upper edge of the instrument cluster
overlay, between the tachometer and the speedome-
ter. The high beam indicator consists of a stenciled
cutout of the International Control and Display Sym-
bol icon for ªHigh Beamº 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 blue lens behind
the cutout in the opaque layer of the overlay causes
the icon to appear in blue through the translucent
outer layer of the overlay when it is illuminated from
behind by a replaceable incandescent bulb and bulb
holder unit located on the instrument cluster elec-
tronic circuit board. The high beam indicator is ser-
viced as a unit with the instrument cluster.
OPERATION
The high beam indicator gives an indication to the
vehicle operator when the headlamp high beams are
illuminated. This indicator is hard wired on the
instrument cluster electronic circuit board, and is
controlled by a headlamp beam select switch input to
the cluster. The headlamp high beam indicator bulb
receives battery current on the instrument cluster
electronic circuit board through a fused B(+) circuit
at all times; therefore, the indicator remains opera-
tional regardless of the ignition switch position. The
headlamp beam select switch is integral to the multi-
function switch on the left side of the steering col-
umn, and is connected in series between ground and
the headlamp high beam indicator. The indicator
bulb only illuminates when it is provided with a path
to ground through the high beam indicator driver cir-
cuit by the headlamp beam select switch. (Refer to 8
- ELECTRICAL/LAMPS/LIGHTING - EXTERIOR/
MULTI-FUNCTION SWITCH - OPERATION). The
high beam indicator can be diagnosed using conven-
tional diagnostic tools and methods.
DIAGNOSIS AND TESTING - HIGH BEAM
INDICATOR
The diagnosis found here addresses an inoperative
headlamp high beam indicator condition. If the prob-
lem being diagnosed is related to inoperative head-
lamp high beams, be certain to repair the headlamp
system before attempting to diagnose or repair the
BR/BEINSTRUMENT CLUSTER 8J - 21
GEAR SELECTOR INDICATOR (Continued)

GARAGE DOOR OPENER STORAGE BIN
A compartment near the front of the overhead con-
sole is designed to hold most garage door opener
remote control transmitters. The transmitter is
mounted within the compartment with an adhesive-
backed hook and loop fastener patch and, when the
compartment is closed, a push button in the center of
the compartment door is depressed to actuate the
transmitter.
A transmitter mounting kit including the adhesive-
backed hook and loop fastener material is available
for service. The garage door opener storage bin door
and the push button with three assorted length
adapter pegs are also available for service replace-
ment.
The garage door opener storage compartment door
is opened by pressing the integral latch towards the
front of the vehicle. When the compartment door is
opened, the push button unit is removed from the
compartment by squeezing the latch tabs and pulling
the unit downward. With the push button removed,
the garage door opener can be installed in the com-
partment using the adhesive-backed hook and loop
fastener material provided.
With the transmitter mounted in the storage bin,
adapter pegs located on the garage door opener push
button unit are selected and mounted on one of two
posts on the back side of the push button. The com-
bination of the adapter peg length and the push but-
ton post location must be suitable to depress the
button of the transmitter when the push button in
the center of the garage door opener storage bin door
is depressed. When the proper combination has been
selected, the push button is reinstalled in the com-
partment and the compartment door is closed.
SUNGLASS STORAGE BIN
A sunglasses storage bin is included in the over-
head console. The storage bin is located near the rear
of the overhead console and is held in the closed posi-
tion by a latch that is integral to the storage bin
door. The interior of the bin is lined with a foam rub-
ber padding material to protect the sunglasses from
being scratched. Dampening springs that are located
on the back of the overhead console reading andcourtesy lamp housing contact the hinges of the sun-
glasses storage bin for a smooth opening action.
The sunglasses storage bin and door unit is avail-
able for service replacement. The hinge dampening
springs are serviced as a unit with the overhead con-
sole reading and courtesy lamp housing.
The sunglasses storage bin is opened by pressing
the latch on the rear edge of the door towards the
front of the vehicle, then pulling the bin downward to
the open position. The integral latch on the sun-
glasses bin door will automatically engage when the
bin is closed. See the owner's manual in the vehicle
glove box for more information on the use and oper-
ation of the sunglasses storage bin.
COMPASS
While in the compass/temperature mode, the com-
pass will display the direction in which the vehicle is
pointed using the eight major compass headings
(Examples: north is N, northeast is NE), along with
the outside ambient temperature. When the compass
unit is placed in the compass/compass in degrees
mode, the compass will display the direction the
vehicle is heading using the eight major compass
headings and in degrees (0 to 359 degrees). North is
0 degrees, East is 90 degrees, South is 180 degrees
and West is 270 degrees. It will not display the head-
ings in minutes or seconds.
The self-calibrating compass unit requires no
adjusting in normal use. The compass unit will com-
pensate for magnetism the body of the vehicle may
acquire during normal 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 procession flag can exceed the compen-
sating ability of the compass unit if placed on the
roof panel. If the vehicle roof should become magne-
tized, the demagnetizing and calibration procedures
found in this group may be required to restore proper
compass operation.
THERMOMETER
The thermometer displays the outside ambient
temperature in whole degrees. The temperature dis-
play can be changed from Fahrenheit to Celsius
1 - SUNGLASSES STORAGE BIN
2 - GARAGE DOOR OPENER STORAGE BIN DOOR
3 - COMPUTER LENS OR COVER PLUG
4 - HOOK AND LOOP FASTENER
5 - SECURITY INDICATOR LAMP
6 - COMPASS MINI-TRIP COMPUTER MODULE
7 - SCREW (3)
8 - SCREW (4)
9 - BULB HOLDERS10 - SWITCHES
11 - WIRE HARNESS
12 - SPRINGS (2)
13 - READING AND COURTESY LAMP HOUSING
14 - REFLECTORS
15 - OVERHEAD CONSOLE HOUSING
16 - LENSES
17 - BUMPER
18 - GARAGE DOOR OPENER PUSH BUTTON
BR/BEMESSAGE SYSTEMS 8M - 3
OVERHEAD CONSOLE (Continued)