2003 JEEP GRAND CHEROKEE Seat position

DIAGNOSIS AND TESTING - HEATED SEAT
ELEMENT
RESISTOR WIRE ELEMENT
(1) Disconnect and isolate the battery negative
cable. The power seat wire harness connectors for the
seat cushion and seat back heating elements are
secured to a bracket located under the rear edge of
the seat cushion frame. Refer toWiringfor complete
circuit schematics and connector locations.
(2) Disconnect the Heated Seat Module (HSM) or
Memory Heated Seat Module (MHSM) C2 connector.
Check for continuity between the SEAT HEATER
B(+) DRIVER circuit cavity of the C2 connector and
the seat cushion frame. There should be NO continu-
ity. If OK, go to Step 3. If not OK, repair the shorted
seat heater B(+) driver circuit as required.
NOTE: WHEN CHECKING HEATED SEAT ELE-
MENTS FOR CONTINUITY, BE CERTAIN TO MOVE
THE HEATING ELEMENT BEING CHECKED. MOV-
ING THE ELEMENT, SUCH AS SITTING IN THE SEAT
WILL ELIMINATE THE POSSIBILITY OF AN INTER-
MITTENT OPEN IN THE ELEMENT WHICH WOULD
ONLY BE EVIDENT IF THE ELEMENT WAS MOVED
IN A CERTAIN DIRECTION. FAILURE TO CHECK
THE ELEMENT IN VARIOUS POSITIONS COULD
RESULT IN AN INCOMPLETE TEST.
(3) Check for continuity between the SEAT
HEATER B(+) DRIVER circuit cavity of the C2 con-
nector and the ground circuit cavity. There should be
continuity at all times (even upon moving or sitting
in the seat). If OK, proceed with testing the other
components in the heated seat system. If not OK,
replace the open heating element. Refer to the proce-
dure in this section of the manual.
REMOVAL
(1) Disconnect and isolate the negative battery
cable.
(2) Remove the appropriate seat cushion or seat
back trim cover. Refer to the Body section of the ser-
vice manual for the procedures.
(3) Disconnect the inoperative heated seat cushion
or seat back element electrical connectors.
(4) Gently peel-off defective heater element from
foam cushion.
INSTALLATION
(1) Peel off the adhesive backing on the back of the
replacement heating element and install on cushion
pad in the same location as the original (Fig. 6).
CAUTION: During the installation of the replace-
ment heating element, be very careful not to fold or
crease the element assembly. Folds or creases will
cause premature failure.
(2) Connect the new heating element electrical
connectors (Fig. 6).
(3) Connect the negative battery cable.
(4) Verify heated seat system operation.
(5) Install the appropriate seat cushion or seat
back trim cover. Make certain the seat wire harness
is correctly routed through the seat and seat back.
The excess wire between the cushion and back ele-
ments should be securely tucked between the rear of
the cushion foam and the rear carpet flap of the trim
cover.
Fig. 6 HEATING ELEMENT INSTALLED
1 - SEAT BACK WIRE HARNESS
2 - HEATED SEAT WIRE HARNESS CONNECTOR
3 - HEATED SEAT CUSHION ELEMENT
8G - 14 HEATED SEAT SYSTEMWJ
HEATED SEAT ELEMENT (Continued)

HEATED SEAT SENSOR
DESCRIPTION
The heated seat temperature sensor is a Negative
Temperature Coefficient (NTC) thermistor. One tem-
perature sensor is used for each seat. This tempera-
ture sensor is located in the seat cushion heating
element on all models.
The heated seat temperature sensor cannot be
repaired or adjusted and must be replaced if defec-
tive. The heated seat cushion element must be
replaced if the temperature sensor is defective. Refer
to the procedure in this section of the service man-
ual.
DIAGNOSIS AND TESTING - HEATED SEAT
SENSOR
For complete circuit diagrams, refer toWiring
Diagrams.
(1) Disconnect the Heated Seat Module (HSM) or
Memory Heated Seat Module (MHSM) C1 connector.
Check for continuity between the SEAT SENSOR 5V
SUPPLY circuit cavity and the seat cushion frame.
There should beNOcontinuity. If OK, go to Step 2.
If not OK, repair the shorted seat sensor 5V supply
circuit as required.
(2) Check for continuity between the SEAT SEN-
SOR 5V SUPPLY circuit cavity of the 4-way power
seat wire harness connector and the C1 connector for
the HSM or MHSM. There should be continuity. If
OK, go to Step 3. If not OK, repair the open seat sen-
sor 5V supply circuit as required.
(3) Connect the module electrical connector. Turn
system ON, using a voltmeter, backprobe the HSM or
MHSM C1 connector on the SEAT TEMPERATURE
SENSOR INPUT circuit cavity. Voltage should be
present (2-4 volts). If OK, proceed with testing the
other components in the heated seat system. If not
OK, refer to Heated Seat Module Diagnosis and Test-
ing in the electronic control modules section of this
manual.
REMOVAL
(1) For heated seat sensor replacement procedure
(Refer to 8 - ELECTRICAL/HEATED SEATS/
HEATED SEAT ELEMENT - REMOVAL).
PASSENGER HEATED SEAT
SWITCH
DESCRIPTION
The heated seat switches are mounted in the
instrument panel center lower bezel (Fig. 7), which is
located near the bottom of the instrument panel cen-
ter stack. The two three-position rocker-type
switches, one switch for each front seat, provide a
resistor multiplexed signal to the Body Control Mod-
ule (BCM) through separate hard wired circuits.
Each switch has an Off, Low, and High position so
that both the driver and the front seat passenger can
select a preferred seat heating mode. Each switch
has two Light-Emitting Diodes (LED), one each for
the Low position and the High position, which light
to indicate that the heater for the seat that the
switch controls is turned on. Each switch is also back
lit by a replaceable incandescent bulb.
The heated seat switches and their LEDs cannot
be repaired. If either switch or LED is faulty or dam-
aged, the entire switch unit must be replaced. The
incandescent switch illumination bulb and bulb
holder units are available for service replacement.
Fig. 7 HEATED SEAT SWITCHES
1 - HEATED SEAT SWITCHES
WJHEATED SEAT SYSTEM 8G - 15

OPERATION
There are three positions that can be selected with
each of the heated seat switches: Off, Low, or High.
When the top of the switch rocker is fully depressed,
the High position is selected and the high position
LED indicator illuminates. When the bottom of the
switch rocker is fully depressed, the Low position is
selected and the low position LED indicator illumi-
nates. When the switch rocker is moved to its neutral
position, Off is selected and both LED indicators are
extinguished.
Both switches provide separate resistor multi-
plexed hard wire inputs to the BCM to indicate the
selected switch position. The BCM monitors the
switch inputs and sends heated seat switch status
messages to the Heated Seat Module (HSM) or the
Memory Heated Seat Module (MHSM) over the Pro-
grammable Communications Interface (PCI) data
bus. The HSM or MHSM responds to the heated seat
switch status messages by controlling the output to
the seat heater elements of the selected seat. The
Low heat position set point is about 36É C (97É F),
and the High heat position set point is about 41É C
(105É F).
DIAGNOSIS AND TESTING - PASSENGER
HEATED SEAT SWITCH
For complete circuit diagrams, refer toWiring
Diagrams.
WARNING: REFER TO THE RESTRAINTS SECTION
OF THIS MANUAL BEFORE ATTEMPTING ANY
STEERING WHEEL, STEERING COLUMN, OR
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Check the fused ignition switch output (run)
fuse in the junction block. If OK, go to Step 2. If not
OK, repair the shorted circuit or component as
required and replace the faulty fuse.
(2) Turn the ignition switch to the On position.
Check for battery voltage at the fused ignition switch
output (run) fuse in the junction block. If OK, go to
Step 3. If not OK, repair the open fused ignition
switch output (run) circuit to the ignition switch as
required.
(3) Disconnect and isolate the battery negative
cable. Remove the lower center bezel from the instru-
ment panel and disconnect the instrument panel wire
harness connectors from both heated seat switch con-
nector receptacles. Check for continuity between the
ground circuit cavity of the instrument panel wire
harness connector for the inoperative heated seatswitch(es) and a good ground. There should be conti-
nuity. If OK, go to Step 4. If not OK, repair the open
ground circuit to ground as required.
(4) Reconnect the battery negative cable. Turn the
ignition switch to the On position. Check for battery
voltage at the fused ignition switch output (run) cir-
cuit cavity of the instrument panel wire harness con-
nector for the inoperative heated seat switch(es). If
OK, turn the ignition switch to the Off position, dis-
connect and isolate the battery negative cable, and go
to Step 5. If not OK, repair the open fused ignition
switch output (run) circuit to the junction block fuse
as required.
(5) Test the heated seat switch(es) (Fig. 8) as
shown in the Heated Seat Switch Test chart. If OK,
go to Step 6. If not OK, replace the faulty heated seat
switch(es).
HEATED SEAT SWITCH TEST
SWITCH
POSITIONRESISTANCE
BETWEENRESISTANCE
(OHMS)
Off Pin1&6 55
Low Pin1&61430
High Pin1&6 365
All resistance values are  5%.
Fig. 8 Rear of Heated Seat Switch
1 - LEFT SHOWN (RIGHT TYPICAL)
2 - ILLUMINATION LAMP
3 - CONNECTOR RECEPTACLE
4 - HEATED SEAT SWITCH
8G - 16 HEATED SEAT SYSTEMWJ
PASSENGER HEATED SEAT SWITCH (Continued)

(6) Disconnect the 22-way instrument panel wire
harness connector from the Body Control Module
(BCM) connector receptacle. Check for continuity
between the seat heater switch sensor ground circuit
cavity of the instrument panel wire harness connec-
tor for the inoperative heated seat switch(es) and a
good ground. There should be no continuity. If OK, go
to Step 7. If not OK, repair the shorted seat heater
switch sensor ground circuit as required.
(7) Check for continuity between the seat heater
switch sensor ground circuit cavities of the instru-
ment panel wire harness connector for the in opera-
tive heated seat switch(es) and the 22-way
instrument panel wire harness connector for the
BCM. There should be continuity. If OK, go to Step 8.
If not OK, repair the open seat heater switch sensor
ground circuit as required.
(8) Check for continuity between the seat heater
switch mux circuit cavity of the instrument panel
wire harness connector for the inoperative heated
seat switch and a good ground. There should be no
continuity. If OK, go to Step 9. If not OK, repair the
shorted seat heater switch mux circuit as required.
(9) Check for continuity between the seat heater
switch mux circuit cavity of the instrument panel
wire harness connector for the inoperative heated
seat switch and the 22-way instrument panel wire
harness connector for the BCM. There should be con-
tinuity. If OK, use a DRBtscan tool and the proper
Diagnostic Procedures manual to test the BCM. If
not OK, repair the open seat heater switch mux cir-
cuit as required.
REMOVAL
WARNING: REFER TO THE RESTRAINTS SECTION
OF THIS MANUAL BEFORE ATTEMPTING ANY
STEERING WHEEL, STEERING COLUMN, OR
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the center lower bezel from the instru-
ment panel. Refer toInstrument Panel CenterLower Bezelin the Body section of this manual for
the procedure.
(3) Remove the four screws that secure the heated
seat switch to the back of the instrument panel cen-
ter lower bezel (Fig. 9).
(4) Remove the heated seat switch from the back
of the instrument panel center lower bezel.INSTALLATION
(1) Position the heated seat switch onto the back
of the instrument panel center lower bezel.
(2) Install and tighten the four screws that secure
the heated seat switch to the back of the instrument
panel center lower bezel. Tighten the screws to 1.5
N´m (13 in. lbs.).
(3) Install the center lower bezel onto the instru-
ment panel. Refer toInstrument Panel Center
Lower Bezelin the Body section of this manual for
the procedure.
(4) Reconnect the battery negative cable.
Fig. 9 Heated Seat Switch Remove/Install
1 - HEATED SEAT SWITCHES
2 - SCREWS (4)
3 - CENTER LOWER BEZEL
4 - CIGAR LIGHTER
5 - ILLUMINATION LAMPS
6 - POWER OUTLET
WJHEATED SEAT SYSTEM 8G - 17
PASSENGER HEATED SEAT SWITCH (Continued)

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO ELECTRICAL, RESTRAINTS
BEFORE ATTEMPTING ANY STEERING WHEEL,
STEERING COLUMN, OR INSTRUMENT PANEL
COMPONENT DIAGNOSIS OR SERVICE. FAILURE
TO TAKE THE PROPER PRECAUTIONS COULD
RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT
AND POSSIBLE PERSONAL INJURY.
(1) Remove the horn relay from the PDC. (Refer to
8 - ELECTRICAL/HORN/HORN RELAY -
REMOVAL) for the procedures.
(2) A relay in the de-energized position should
have continuity between terminals 87A and 30, and
no continuity between terminals 87 and 30. If OK, go
to Step 3. If not OK, replace the faulty relay.
(3) Resistance between terminals 85 and 86 (elec-
tromagnet) should be 75   5 ohms. If OK, go to Step
4. If not OK, replace the faulty relay.
(4) Connect a battery to terminals 85 and 86.
There should now be continuity between terminals
30 and 87, and no continuity between terminals 87A
and 30. If OK, perform the Relay Circuit Test that
follows. If not OK, replace the faulty relay.
RELAY CIRCUIT TEST
(1) The relay common feed terminal cavity (30) is
connected to battery voltage and should be hot at all
times. If OK, go to Step 2. If not OK, repair the open
circuit to the fuse in the PDC as required.
(2) The relay normally closed terminal (87A) is
connected to terminal 30 in the de-energized position,
but is not used for this application. Go to Step 3.(3) The relay normally open terminal (87) is con-
nected to the common feed terminal (30) in the ener-
gized position. This terminal supplies battery voltage
to the horn(s). There should be continuity between
the cavity for relay terminal 87 and the horn relay
output circuit cavity of each horn wire harness con-
nector at all times. If OK, go to Step 4. If not OK,
repair the open circuit to the horn(s) as required.
(4) The coil battery terminal (86) is connected to
the electromagnet in the relay. It is connected to bat-
tery voltage and should be hot at all times. Check for
battery voltage at the cavity for relay terminal 86. If
OK, go to Step 5. If not OK, repair the open circuit to
the fuse in the PDC as required.
(5) The coil ground terminal (85) is connected to
the electromagnet in the relay. It is grounded
through the horn switch when the horn switch is
depressed. The horn relay coil ground terminal can
also be grounded by the Body Control Module (BCM)
in response to certain inputs related to the RKE sys-
tem or the Vehicle Theft Security System. Check for
continuity to ground at the cavity for relay terminal
85. There should be continuity with the horn switch
depressed, and no continuity with the horn switch
released. If not OK, (Refer to 8 - ELECTRICAL/
HORN/HORN SWITCH - DIAGNOSIS AND TEST-
ING).
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the cover from the Power Distribution
Center (PDC) (Fig. 3) .
(3) See the fuse and relay layout label affixed to
the underside of the PDC cover for horn relay iden-
tification and location.
(4) Remove the horn relay from the PDC.
INSTALLATION
(1) See the fuse and relay layout label affixed to
the underside of the PDC cover for the proper horn
relay location.
(2) Position the horn relay in the proper receptacle
in the PDC.
(3) Align the horn relay terminals with the termi-
nal cavities in the PDC receptacle.
(4) Push down firmly on the horn relay until the
terminals are fully seated in the terminal cavities in
the PDC receptacle.
(5) Install the cover onto the PDC.
(6) Reconnect the battery negative cable.
Fig. 2 Horn Relay
30 - COMMON FEED
85 - COIL GROUND
86 - COIL BATTERY
87 - NORMALLY OPEN
87A - NORMALLY CLOSED
WJHORN 8H - 5
HORN RELAY (Continued)

OPERATION
The ElectroMechanical Instrument Cluster (EMIC)
is designed to allow the vehicle operator to monitor
the conditions of many of the vehicle components and
operating systems. The gauges and indicators in the
EMIC provide valuable information about the various
standard and optional powertrains, fuel and emis-
sions systems, cooling systems, lighting systems,
safety systems and many other convenience items.
The EMIC is installed in the instrument panel so
that all of these monitors can be easily viewed by the
vehicle operator when driving, while still allowing
relative ease of access for service. The microproces-
sor-based EMIC hardware and software uses various
inputs to control the gauges and indicators visible on
the face of the cluster. Some of these inputs are hard
wired, but most are in the form of electronic mes-
sages that are transmitted by other electronic mod-ules over the Programmable Communications
Interface (PCI) data bus network. (Refer to 8 -
ELECTRICAL/ELECTRONIC CONTROL MOD-
ULES/COMMUNICATION - OPERATION).
The EMIC microprocessor smooths the input data
using algorithms to provide gauge readings that are
accurate, stable and responsive to operating condi-
tions. These algorithms are designed to provide
gauge readings during normal operation that are con-
sistent with customer expectations. However, when
abnormal conditions exist, such as low or high bat-
tery voltage, low oil pressure or high coolant temper-
ature, the algorithm can drive the gauge pointer to
an extreme position and the microprocessor turns on
the Check Gauges indicator to provide a distinct
visual indication of a problem to the vehicle operator.
The instrument cluster circuitry also sends electronic
chime tone request messages over the PCI data bus
to the Body Control Module (BCM) when it monitors
Fig. 2 EMIC Gauges & Indicators
1 - BRAKE INDICATOR 15 - TRANSMISSION OVERTEMP INDICATOR
2 - REAR FOG LAMP INDICATOR 16 - PART TIME 4WD INDICATOR
3 - WATER-IN-FUEL INDICATOR 17 - CHECK GAUGES INDICATOR
4 - VOLTAGE GAUGE 18 - ENGINE TEMPERATURE GAUGE
5 - LEFT TURN INDICATOR 19 - ODOMETER/TRIP ODOMETER SWITCH BUTTON
6 - TACHOMETER 20 - ODOMETER/TRIP ODOMETER DISPLAY
7 - HIGH BEAM INDICATOR 21 - WAIT-TO-START INDICATOR
8 - AIRBAG INDICATOR 22 - OVERDRIVE-OFF INDICATOR
9 - SPEEDOMETER 23 - SEATBELT INDICATOR
10 - RIGHT TURN INDICATOR 24 - ABS INDICATOR
11 - OIL PRESSURE GAUGE 25 - FUEL GAUGE
12 - SKIS INDICATOR 26 - FRONT FOG LAMP INDICATOR
13 - MALFUNCTION INDICATOR LAMP (MIL) 27 - LOW FUEL INDICATOR
14 - CRUISE INDICATOR 28 - COOLANT LOW INDICATOR
8J - 4 INSTRUMENT CLUSTERWJ
INSTRUMENT CLUSTER (Continued)

WARNING: ON VEHICLES EQUIPPED WITH THE
PREMIUM INSTRUMENT CLUSTER, THE CLUSTER
CIRCUITRY PROVIDES AN ALTERNATING CURRENT
TO SUPPLY POWER TO THE ELECTRO-LUMINES-
CENT ILLUMINATION LAMP THROUGH A PIGTAIL
WIRE AND CONNECTOR THAT IS ACCESSIBLE AT
THE BACK OF THE CLUSTER HOUSING. USE
PROPER PRECAUTIONS WHEN HANDLING THIS
UNIT DURING DIAGNOSIS OR SERVICE TO AVOID
ELECTRICAL SHOCK AND POSSIBLE PERSONAL
INJURY.
CLUSTER BULB
This procedure applies to each of the incandescent
cluster illumination lamp or indicator bulb and bulb
holder units. However, the illumination lamps and
the indicators use different bulb and bulb holder unit
sizes. They must never be interchanged.
CAUTION: Be certain that any bulb and bulb holder
unit removed from the cluster electronic circuit
board is reinstalled in the correct position. Always
use the correct bulb size and type for replacement.
An incorrect bulb size or type may overheat and
cause damage to the instrument cluster, the elec-
tronic circuit board and/or the gauges.
(1) Insert the bulb and bulb holder straight into
the correct bulb mounting hole in the cluster elec-
tronic circuit board (Fig. 4).
(2) With the bulb holder fully seated against the
cluster electronic circuit board, turn the bulb holder
clockwise about sixty degrees to lock it into place.
(3) Reinstall the instrument cluster onto the
instrument panel. (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - INSTALLATION).
(4) Reconnect the battery negative cable.
CLUSTER LENS, HOOD AND MASK
(1) Position the cluster lens, hood and mask unit
over the face of the instrument cluster (Fig. 5). Be
certain that the odometer/trip odometer switch but-
ton is inserted through the proper clearance holes in
the mask and the lens.
(2) Press firmly and evenly on the cluster lens,
hood and mask unit to install it onto the cluster
housing.
(3) Work around the perimeter of the cluster hous-
ing to be certain that each of the eight latches that
secure the cluster lens, hood and mask unit to the
cluster housing is fully engaged.
(4) Reinstall the instrument cluster into the
instrument panel. (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - INSTALLATION).
(5) Reconnect the battery negative cable.CLUSTER HOUSING REAR COVER
(1) Position the rear cover onto the back of the
cluster housing (Fig. 6).
(2) Press firmly and evenly on the rear cover until
each of the eight latches (four on top, four on the bot-
tom) that secure the upper and lower edges of the
rear cover to the top and bottom of the cluster hous-
ing are fully engaged.
(3) Install and tighten the seven screws that
secure the rear cover to the back of the cluster hous-
ing. Tighten the screws to 2 N´m (20 in. lbs.).
(4) On models with a premium cluster only, recon-
nect the electro-luminescent illumination lamp pig-
tail wire connector to the receptacle on the cluster
electronic circuit board and engage the pigtail wire
under the integral routing clip on the rear cover.
(5) Reinstall the instrument cluster onto the
instrument panel. (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - INSTALLATION).
(6) Reconnect the battery negative cable.
INSTALLATION
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,
PASSENGER AIRBAG, SIDE CURTAIN AIRBAG,
FRONT IMPACT SENSOR, SIDE IMPACT SENSOR,
OR INSTRUMENT PANEL COMPONENT DIAGNOSIS
OR SERVICE. DISCONNECT AND ISOLATE THE
BATTERY NEGATIVE (GROUND) CABLE, THEN
WAIT TWO MINUTES FOR THE SYSTEM CAPACI-
TOR TO DISCHARGE BEFORE PERFORMING FUR-
THER DIAGNOSIS OR SERVICE. THIS IS THE ONLY
SURE WAY TO DISABLE THE SUPPLEMENTAL
RESTRAINT SYSTEM. FAILURE TO TAKE THE
PROPER PRECAUTIONS COULD RESULT IN ACCI-
DENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.
WARNING: ON VEHICLES EQUIPPED WITH THE
PREMIUM INSTRUMENT CLUSTER, THE CLUSTER
CIRCUITRY PROVIDES AN ALTERNATING CURRENT
TO SUPPLY POWER TO THE ELECTRO-LUMINES-
CENT ILLUMINATION LAMP THROUGH A PIGTAIL
WIRE AND CONNECTOR THAT IS ACCESSIBLE AT
THE BACK OF THE CLUSTER HOUSING. USE
PROPER PRECAUTIONS WHEN HANDLING THIS
UNIT DURING DIAGNOSIS OR SERVICE TO AVOID
ELECTRICAL SHOCK AND POSSIBLE PERSONAL
INJURY.
(1) Position the instrument cluster to the instru-
ment panel.
8J - 12 INSTRUMENT CLUSTERWJ
INSTRUMENT CLUSTER (Continued)

then sends the proper rear fog lamp indicator
lamp-on and lamp-off messages to the instrument
cluster. If the rear fog lamp indicator fails to light
during the actuator test, replace the bulb with a
known good unit. For further diagnosis of the rear
fog lamp indicator or the instrument cluster circuitry
that controls the indicator, (Refer to 8 - ELECTRI-
CAL/INSTRUMENT CLUSTER - DIAGNOSIS AND
TESTING). For proper diagnosis of the rear fog lamp
system, the BCM, the PCI data bus, or the electronic
message inputs to the instrument cluster that control
the rear fog lamp indicator, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
SEATBELT INDICATOR
DESCRIPTION
A seatbelt indicator is standard equipment on all
instrument clusters. The seatbelt indicator is located
near the lower edge of the instrument cluster, to the
left of the tachometer. The seatbelt indicator consists
of an International Control and Display Symbol icon
for ªSeat Beltº imprinted on a red lens. The lens is
located behind a cutout in the opaque layer of the
instrument cluster overlay. The dark outer layer of
the overlay prevents the icon from being clearly vis-
ible when the indicator is not illuminated. The icon
appears silhouetted against a red field through the
translucent outer layer of the overlay when it is illu-
minated from behind by a Light Emitting Diode
(LED), which is soldered onto the instrument cluster
electronic circuit board. The seatbelt indicator lens is
serviced as a unit with the instrument cluster lens,
hood and mask unit.
OPERATION
The seatbelt indicator gives an indication to the
vehicle operator of the status of the driver side front
seatbelt. This indicator is controlled by a transistor
on the instrument cluster electronic circuit board
based upon cluster programming. On models
equipped with airbags the indicator is also controlled
by electronic messages received by the cluster from
the Airbag Control Module (ACM) over the Program-
mable Communications Interface (PCI) data bus. The
seatbelt indicator Light Emitting Diode (LED) is
completely controlled by the instrument cluster logic
circuit, and that logic will only allow this indicator to
operate when the instrument cluster receives a bat-
tery current input on the fused ignition switch out-
put (run-start) circuit. Therefore, the indicator willalways be off when the ignition switch is in any posi-
tion except On or Start. The LED only illuminates
when it is provided a path to ground by the instru-
ment cluster transistor. The instrument cluster will
turn on the seatbelt indicator for the following rea-
sons:
²Seatbelt Reminder Function- Each time the
cluster receives a battery current input on the fused
ignition switch output (run-start) circuit, the indica-
tor will be illuminated as a seatbelt reminder for
about six seconds, or until the ignition switch is
turned to the Off position, whichever occurs first.
This reminder function will occur regardless of the
status of the electronic seat belt lamp-on or lamp-off
messages received by the cluster from the ACM.
²Seat Belt Indicator Lamp-On Message-On
models equipped with airbags, following the seatbelt
reminder function, each time the cluster receives a
seat belt indicator lamp-on message from the ACM
indicating the driver side front seat belt is not fas-
tened with the ignition switch in the Start or On
positions, the seatbelt indicator will be illuminated.
The indicator remains illuminated until the cluster
receives a seat belt indicator lamp-off message from
the ACM, or until the ignition switch is turned to the
Off position, whichever occurs first.
²Actuator Test- Each time the cluster is put
through the actuator test, the seatbelt indicator will
be turned on for the duration of the test to confirm
the functionality of the LED and the cluster control
circuitry.
The instrument cluster continually monitors the
status of the ignition switch through the hard wired
fused ignition switch output (run-start) circuit to
determine when to provide the seatbelt reminder
function. On models equipped with airbags, the ACM
continually monitors the status of both front seat belt
switches to determine the proper airbag system
response to a frontal impact of the vehicle. The ACM
then sends the proper seatbelt indicator lamp-on and
lamp-off messages to the instrument cluster based
upon the status of the driver side front seat belt
switch input. For further diagnosis of the seatbelt
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 seatbelt
switches, the ACM, the PCI data bus, or the elec-
tronic message inputs to the instrument cluster that
control the seatbelt indicator, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
8J - 28 INSTRUMENT CLUSTERWJ
REAR FOG LAMP INDICATOR (Continued)