2002 JEEP LIBERTY display

sunroof, the sunroof switch is located between the
two reading and courtesy lamps. The overhead con-
sole is mounted with one screw and two snap clips to
a molded plastic retainer bracket located above the
headliner.
OPERATION
Refer to the vehicle Owner's Manual for specific
operation of each overhead console and its systems.
STANDARD PROCEDURE
STANDARD PROCEDURE - CMTC LAMP
REPLACEMENT
(1) Open hood, disconnect and isolate the negative
battery cable.
(2) Remove overhead console (Refer to 8 - ELEC-
TRICAL/OVERHEAD CONSOLE - REMOVAL).
(3) Using a flat blade screwdriver twist out the
lamp socket.
(4) Replace lamp(s) as necessary.
STANDARD PROCEDURE - COURTESY LAMP
REPLACEMENT
(1) Open hood, disconnect and isolate the negative
battery cable.
(2) Remove the overhead console from the head-
liner (Refer to 8 - ELECTRICAL/OVERHEAD CON-
SOLE - REMOVAL).
(3) Remove the lamp and socket assembly from the
overhead console.
(4) Remove the lamp bulb by pulling it straight
out of its socket.
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
(CMTC) modules must have their compass calibrated
using this procedure. Do not attempt to calibrate the
compass near large metal objects such as other vehi-
cles, large buildings, or bridges; or, near overhead or
underground power lines.
NOTE: Whenever the compass is calibrated manu-
ally, the variance number must also be reset. Refer
to Compass Variation Adjustment in this group.
Calibrate the compass manually as follows:
(1) Turn the ignition switch to the On position. If
the compass/thermometer data is not currently being
displayed, momentarily depress and release the C/T
push button to reach the compass/thermometer dis-
play.
(2) Depress the Reset push button and hold the
button down until ªCALº appears in the display. This
takes about ten seconds, and appears about five sec-
onds after ªVARIANCE = XXº is displayed.
(3) Release the Reset push button.
(4) Drive the vehicle on a level surface, away from
large metal objects and power lines, through three or
more complete circles at between five and eight kilo-
meters-per-hour (three and five miles-per-hour) in
not less than 48 seconds. The ªCALº message will
disappear from the display to indicate that the com-
pass is now calibrated.
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 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
DEMAGNETIZING
A degaussing tool (Special Tool 6029) is used to
demagnetize, or degauss, the overhead console for-
ward mounting screw and the roof panel above the
overhead console. Equivalent units must be rated as
Fig. 3 Base Console
8M - 2 MESSAGE SYSTEMSKJ
OVERHEAD CONSOLE (Continued)

continuous duty for 110/115 volts and 60 Hz. They
must also have a field strength of over 350 gauss at 7
millimeters (0.25 inch) beyond the tip of the probe.
To demagnetize the roof panel and the overhead
console forward mounting screw, proceed as follows:
(1) Be certain that the ignition switch is in the Off
position, before you begin the demagnetizing proce-
dure.
(2) Connect the degaussing tool to an electrical
outlet, while keeping the tool at least 61 centimeters
(2 feet) away from the compass unit.
(3) Slowly approach the head of the overhead con-
sole forward mounting screw with the degaussing
tool connected.
(4) Contact the head of the screw with the plastic
coated tip of the degaussing tool for about two sec-
onds.
(5) With the degaussing tool still energized, slowly
back it away from the screw. When the tip of the tool
is at least 61 centimeters (2 feet) from the screw
head, disconnect the tool.
(6) Place a piece of paper approximately 22 by 28
centimeters (8.5 by 11 inches), oriented on the vehicle
lengthwise from front to rear, on the center line of
the roof at the windshield header (Fig. 4). The pur-
pose of the paper is to protect the roof panel from
scratches, and to define the area to be demagnetized.
(7) Connect the degaussing tool to an electrical
outlet, while keeping the tool at least 61 centimeters
(2 feet) away from the compass unit.
(8) Slowly approach the center line of the roof
panel at the windshield header, with the degaussing
tool connected.
(9) Contact the roof panel with the plastic coated
tip of the degaussing tool. Be sure that the template
is in place to avoid scratching the roof panel. Using a
slow, back-and-forth sweeping motion, and allowing
13 millimeters (0.50 inch) between passes, move the
tool at least 11 centimeters (4 inches) to each side of
the roof center line, and 28 centimeters (11 inches)
back from the windshield header.
(10) With the degaussing tool still energized,
slowly back it away from the roof panel. When the
tip of the tool is at least 61 centimeters (2 feet) from
the roof panel, disconnect the tool.
(11) Calibrate the compass and adjust the compass
variance (Refer to 8 - ELECTRICAL/OVERHEAD
CONSOLE - STANDARD PROCEDURE).
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 compassto give false readings. If this problem occurs, the
compass variance setting may need to be changed.
To set the compass variance:
(1) Using the Variance Settings map, find your
geographic location and note the zone number (Fig.
5).
(2) Turn the ignition switch to the On position. If
the compass/thermometer data is not currently being
displayed, momentarily depress and release the C/T
push button to reach the compass/thermometer dis-
play.
(3) Depress the Reset push button and hold the
button down until ªVARIANCE = XXº appears in the
display. This takes about five seconds.
(4) Release the Reset push button. ªVARIANCE
=XX º will remain in the display. ªXXº equals the cur-
rent variance zone setting.
(5) Momentarily depress and release the Step push
button to step through the zone numbers, until the
zone number for your geographic location appears in
the display.
(6) Momentarily depress and release the Reset
push button to enter the displayed zone number into
the CMTC module memory.
(7) Confirm that the correct directions are now
indicated by the compass.
Fig. 4 Roof Demagnetizing Pattern
KJMESSAGE SYSTEMS 8M - 3
OVERHEAD CONSOLE (Continued)

REMOVAL
OVERHEAD CONSOLE - REMOVAL
(1) Disconnect and isolate the negative battery
cable.
(2) Remove the overhead console retaining screw,
located in the front of console near the windshield.
(3) Using your fingertips, grasp the sides of the
overhead console and pull straight down evenly to
disengage the two snap clips at the rear of the unit.
(4) Lower the overhead console far enough to
access the wire harness connectors.
(5) Disconnect the control module, courtesy lamps
and power sunroof switch electrical connectors, if
equipped.
(6) Remove the overhead console assembly from
the vehicle.
INSTALLATION
(1) Position the overhead console in the vehicle
and connect the wire harness connectors.
(2) Connect the control module, courtesy lamps
and power sunroof switch electrical connectors, if
equipped.
(3) Grasp the sides of the overhead console and
push straight up evenly to engage the two snap clips
at the rear of the unit.
(4) Install the overhead console retaining screw,
located in the front of console near the windshield.
Torque the screw to 1.2 N´m (10 in. lbs.).
(5) Connect the negative battery cable.
COMPASS/MINI-TRIP
COMPUTER
DESCRIPTION
The Compass Mini-Trip Computer (CMTC) is
located in the overhead console on models equipped
with this option. The Compass Mini-Trip Computer
module features a large Vacuum Fluorescent Display
(VFD) screen for displaying information, and four
back-lit push button function switches labeled C/T
(compass/thermometer), RESET, STEP, and US/M
(United States/Metric Scale).
The Compass Mini-Trip Computer module contains
a central processing unit and interfaces with other
electronic modules in the vehicle over the Program-
mable Communications Interface (PCI) data bus net-
work. The PCI data bus network allows the sharing
of sensor information. This helps to reduce wire har-
ness complexity, reduce internal controller hardware,
and reduce component sensor current loads. At the
same time, this system provides increased reliability,
enhanced diagnostics, and allows the addition of
many new feature capabilities.
The Compass Mini-Trip Computer module contains
six informational displays which can be displayed
using the four outer buttons on the overhead console.
When the vehicle is first turned ON:
²CMTC blanks the display for a half second
²Displays whatever was being viewed when the
ignition was last turned OFF
Fig. 5 Variance Settings
8M - 4 MESSAGE SYSTEMSKJ
OVERHEAD CONSOLE (Continued)

The CMTC may also be integrated with the Uni-
versal Transmitter. If so, your CMTC module will
have three buttons centered together between the
outer four buttons. Below the three buttons are cor-
responding dots to indicate which button you are
using.
The Compass Mini-Trip Computer includes the fol-
lowing display options:
²Compass and thermometer- provides the out-
side temperature and one of eight compass readings
to indicate the direction the vehicle is facing.
²Average fuel economy- shows the average
fuel economy since the last trip computer reset.
²Distance to empty- shows the estimated dis-
tance that can be travelled with the fuel remaining
in the fuel tank. This estimated distance is computed
using the average miles-per-gallon from the last 30
gallons of fuel used.
²Instant fuel economy- shows the present fuel
economy based upon the current vehicle distance and
fuel used information.
²Trip odometer- shows the distance travelled
since the last trip computer reset.
²Elapsed time- shows the accumulated igni-
tion-on time since the last trip computer reset.
²Blank screen- the CMTC compass/thermome-
ter/trip computer VFD is turned off.
If the vehicle is equipped with the optional Univer-
sal Transmitter transceiver, the CMTC will also dis-
play messages and an icon indicating when the
Universal Transmitter is being trained, which of the
three transmitter buttons is transmitting, and when
the transceiver is cleared.
Data input for all CMTC functions, including VFD
dimming level, is received through PCI data bus
messages. The CMTC module uses its internal pro-
gramming and all of its data inputs to calculate and
display the requested data. If the data displayed is
incorrect, perform the self-diagnostic tests as
described in this group. If these tests prove inconclu-
sive, the use of a DRBIIItscan tool and the proper
Diagnostic Procedures manual are recommended for
further testing of the CMTC module and the PCI
data bus.
The CMTC module cannot be repaired, and is
available for service only as a unit. This unit
includes the push button switches and the plastic
module and display lens. If any of these components
is faulty or damaged, the complete CMTC module
must be replaced. The incandescent bulbs used for
CMTC push button back-lighting are available for
service replacement.
DESCRIPTION - COMPASS
While in the compass/thermometer mode, the com-
pass will display the direction in which the vehicle ispointed using the eight major compass headings
(Examples: north is N, northeast is NE). The self-cal-
ibrating compass unit requires no adjusting in nor-
mal use. The only calibration that may prove
necessary is to drive the vehicle in three complete
circles at 5 to 8 kilometers-per-hour (3 to 5 miles-per-
hour), on level ground, in not less than forty-eight
seconds. This will reorient the compass unit to its
vehicle.
The compass unit also will compensate for magne-
tism the body of the vehicle may acquire during nor-
mal use. However, avoid placing anything magnetic
directly on the roof of the vehicle. Magnetic mounts
for an antenna, a repair order hat, or a funeral pro-
cession flag can exceed the compensating ability of
the compass unit if placed on the roof panel. Mag-
netic bit drivers used on the fasteners that hold the
overhead console assembly to the roof header can
also affect compass operation. If the vehicle roof
should become magnetized, the demagnetizing and
calibration procedures found in this group may be
required to restore proper compass operation.
DESCRIPTION - THERMOMETER
The thermometer displays the outside ambient
temperature in whole degrees. The temperature dis-
play can be toggled from Fahrenheit to Celsius by
using the U.S./Metric button. The displayed temper-
ature is not an instant reading of conditions, but an
average temperature. It may take the thermometer
display several minutes to respond to a major tem-
perature 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 Body Control Module (BCM) unit memory. When
the ignition switch is turned to the On position
again, the CMTC will display the memory tempera-
ture for one minute; then update the display to the
current average temperature reading within five
minutes.
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
Body Control Module (BCM). The BCM sends tem-
perature status messages to the CMTC module over
the PCI data bus network. The ambient temperature
sensor is available as a separate service item, refer to
additional information later in this section.
OPERATION
The compass mini-trip computer operates when the
ignition is in the ON position. The VFD will display
the last display before ignition was turned OFF. The
four outer buttons operate:
KJMESSAGE SYSTEMS 8M - 5
COMPASS/MINI-TRIP COMPUTER (Continued)

²STEP
²C/T - Compass/Temperature
²US/M - English/Metric
²RESET
1. STEP BUTTON
Pressing the STEP button selects one of the follow-
ing 6 displays:
²Average fuel economy
²Distance to empty
²Instantaneous fuel economy
²Trip odometer
²Elapsed time
²Blank Screen
2. C/T (COMPASS/TEMPERATURE)
BUTTON
Pressing the C/T button selects the Compass/Tem-
perature display.
3. US/M (ENGLISH/METRIC
MEASUREMENT) BUTTON
Pressing the US/M button switches the display
units between English and Metric readings.
4. RESET BUTTON
Pressing the RESET button resets the function on
the display, provided that function can be reset. The
functions which can be reset are Average fuel econ-
omy, Trip odometer and Elapsed time.
Global ResetThis feature allows all three dis-
plays (Average fuel economy, Trip odometer and
Elapsed time) to be reset easily, by pressing the
RESET button twice within three seconds with any
of the screens in display. This eliminates the need to
reset each display individually.
The RESET button is also used to set the variance
and/or calibrate the compass. Refer to the Variance
Procedure and Calibration Procedure in this section.
For more information on the features, control func-
tions and setting procedures for the CMTC module,
see the owner's manual in the vehicle glove box.
DIAGNOSIS AND TESTING - COMPASS
MINI-TRIP COMPUTER
The following diagnostic procedure can be used if
the compass mini-trip computer is not operational in
any way. If the problem is specific to a individual
CMTC display, go to the appropriate display title
noted below and diagnose using the information pro-
vided on how these displays are generated.
(1) Remove the overhead console from the head-
liner (Refer to 8 - ELECTRICAL/OVERHEAD CON-
SOLE - REMOVAL).
(2) Using a ohmmeter, check the ground circuit
cavity of the compass mini-trip computer electricalconnector for proper continuity to ground. Continuity
should be present, If OK go to Step 3, If not OK
repair the open or shorted ground circuit as required.
NOTE: Connect the negative battery cable before
proceeding.
(3) Using a voltmeter, check the fused (B+) circuit
cavity of the compass mini-trip computer electrical
connector for 12v. Voltage should be present, If OK go
to Step 4, If not OK repair the open or shorted fused
(B+) circuit as required.
(4) Using a voltmeter, check the fused ignition
switch output circuit cavity of the compass mini-trip
computer electrical connector for 12v with Key ON.
Voltage should be present, If OK, replace the inoper-
ative CMTC module, If not OK repair the open or
shorted fused ignition switch output circuit as
required.
TEMPERATURE
The compass mini-trip computer receives Program-
mable Communications Interface bus (PCI bus) mes-
sages from the Body Control Module (BCM) for all
displayed information except the compass display. If
a dash (-) is displayed, the compass mini-trip com-
puter is not receiving a PCI bus message from the
BCM. To check out the PCI bus line and the BCM,
use the DRB llltscan tool and proper Body Diagnos-
tic Procedure Manual.
If the compass mini-trip computer displays a tem-
perature more than 54É C (130É F), check for a short
circuit between the temperature sensor and the
BCM.
If the compass mini-trip computer displays a tem-
perature less than -40É C (-67É F), check for an open
circuit between the temperature sensor and the
BCM.
AVERAGE FUEL ECONOMY
The compass mini-trip computer receives average
fuel economy information from the BCM over the PCI
bus line. If the compass mini-trip computer displays
-.- instead of an average fuel economy value, it is not
receiving a PCI bus message for the average fuel
economy from the BCM. To check out the PCI bus
line and the BCM use the DRB llltscan tool and
proper Body Diagnostic Procedure Manual.
DISTANCE TO EMPTY
The compass mini-trip computer receives distance
to empty information from the BCM over the PCI bus
line. If compass mini-trip computer displays a dash
(-) instead of a distance to empty value, it is not
receiving a PCI bus message for the distance to
empty from the BCM. To check out the PCI bus line
8M - 6 MESSAGE SYSTEMSKJ
COMPASS/MINI-TRIP COMPUTER (Continued)

and the BCM use the DRB llltscan tool and proper
Body Diagnostic Procedure Manual.
INSTANTANEOUS FUEL ECONOMY
The compass mini-trip computer receives instanta-
neous fuel economy information from the BCM over
the PCI bus line. If compass mini-trip computer dis-
plays a dash (-) instead of an instantaneous fuel
economy value, it is not receiving a PCI bus message
for the instantaneous fuel economy from the BCM. To
check out the PCI bus line and the BCM use the
DRB llltscan tool and proper Body Diagnostic Pro-
cedure Manual.
TRIP ODOMETER
The compass mini-trip computer receives trip
odometer information from the Cluster over the PCI
bus line. If compass mini-trip computer displays
dashes - - instead of the trip odometer value, it is not
receiving a PCI bus message for the trip odometer
from the cluster. To check out the PCI bus line and
the Cluster, use the DRB llltscan tool and proper
Body Diagnostic Procedure Manual.
ELAPSED TIME
The compass mini-trip computer receives a PCI
bus message containing elapsed time information. If
compass mini-trip computer displays dashes --
instead of the elapsed time, it is not receiving a PCI
bus message for the elapsed time from the BCM. To
check out the PCI bus line and the BCM, use the
DRB llltscan tool and proper Body Diagnostic Pro-
cedure Manual.
COMPASS DISPLAY
To display the vehicle direction, the compass mini-
trip computer processes information from a sensor
internal to the module. The compass mini-trip com-
puter is self- calibrating and requires only variance
adjustments dependent upon location. The compass
mini-trip computer displays the label CAL whenever
the compass is in the fast calibration mode.
If all three of the following conditions listed below
occur, the vehicle must be demagnetized.
²Compass portion of the display is blank
²Temperature portion of the display is OK
²The label CAL is illuminated
If demagnetizing the vehicle is needed, refer to the
demagnetizing procedure in this section. After
demagnetizing, to calibrate the compass refer to Cal-
ibration Procedure and to set the variance refer to
Variance Procedure, both within this section. If the
compass portion of the display is still blank, replace
the compass mini-trip computer.
COMPASS MINI-TRIP COMPUTER - SELF
DIAGNOSTIC TEST
(1) With the ignition switch in the OFF position
simultaneously press the C/T and STEP buttons and
hold.
(2) Turn the ignition switch ON, then release C/T
and STEP buttons.
(3) The Compass mini-trip computer should light
all segments on the VF Display Screen for 2-4 sec-
onds. Check for segments that are not illuminated.
(4) If the compass mini-trip computer displays
PASS, the module is OK.
(5) If the compass mini-trip computer displays
FAIL, replace the module.
(6) If the compass mini-trip computer displays
bUS, check for an open or a short on the PCI bus
communication circuit.
(7) Press the C/T or the STEP button to exit the
self-diagnostic test.
REMOVAL
(1) Remove overhead console, refer to Console
Removal and Installation in this section.
(2) Remove mounting screws and release the map
lamp wire connector from the compass mini-trip com-
puter. (Fig. 6).
Fig. 6 Compass Mini-Trip Computer Retaining
Screws
1 - LAMPS
2 - MOUNTING SCREWS
KJMESSAGE SYSTEMS 8M - 7
COMPASS/MINI-TRIP COMPUTER (Continued)

(3) Remove the compass mini-trip computer from
the overhead console.
INSTALLATION
(1) Install the compass mini-trip computer in the
overhead console. Align the compass mini-trip com-
puter guides on the housing with the grooves of the
console.
(2) Install the mounting screws and install the
map lamp wire connector on the compass mini-trip
computer. Make sure the LOOP of wire that was
clipped into the compass mini-trip computer module
housing is properly clipped into the new module
before the console is placed back into the headliner.
(3) Install the overhead console, refer to Console
Installation in this section.
UNIVERSAL TRANSMITTER
DESCRIPTION
On some KJ models a Universal Transmitter trans-
ceiver is standard factory-installed equipment. The
universal transmitter transceiver is integral to the
Compass Mini-Trip Computer (CMTC), which is
located in the overhead console. The only visible com-
ponent of the universal transmitter are the three
transmitter push buttons (Fig. 7) centered between
the four CMTC push buttons located just rearward of
the CMTC display screen in the overhead console.
The three universal transmitter push buttons are
identified with one, two or three light indicators so
that they be easily identified by sight or by feel.
Each of the three universal transmitter push but-
tons controls an independent radio transmitter chan-
nel. Each of these three channels can be trained totransmit a different radio frequency signal for the
remote operation of garage door openers, motorized
gate openers, home or office lighting, security sys-
tems or just about any other device that can be
equipped with a radio receiver in the 286 to 399
MegaHertz (MHz) frequency range for remote opera-
tion. The universal transmitter is capable of operat-
ing systems using either rolling code or non-rolling
code technology.
The CMTC module displays messages and a small
house-shaped icon with one, two or three dots corre-
sponding to the three transmitter buttons to indicate
the status of the Universal Transmitter.
The Universal Transmitter cannot be repaired, and
is available for service only as a unit with the CMTC
module. This unit includes the push button switches
and the plastic module and display lens. If any of
these components is faulty or damaged, the complete
CMTC module must be replaced.
OPERATION
The universal transmitter operates on a non-
switched source of battery current so the unit will
remain functional, regardless of the ignition switch
position. For more information on the features, pro-
gramming procedures and operation of the universal
transmitter, see the owner's manual in the vehicle
glove box.
DIAGNOSIS AND TESTING - UNIVERSAL
TRANSMITTER
If the Universal Transmitter is inoperative, but the
Compass Mini-Trip Computer (CMTC) is operating
normally, see the owner's manual in the vehicle glove
box for instructions on training the universal trans-
mitter. Retrain the universal transmitter with a
known good transmitter as instructed in the owner's
manual and test the universal transmitter operation
again. If the unit is still inoperative, replace the
faulty universal transmitter and CMTC module as a
unit. If both the universal transmitter and the CMTC
module are inoperative, refer toDiagnosis and
Testing the Compass Mini-Trip Computerin this
section for further diagnosis. For complete circuit
diagrams, refer toOverhead Consolein Wiring
Diagrams.
STANDARD PROCEDURE
STANDARD PROCEDURE - ERASING
TRANSMITTER CODES
To erase the universal transmitter codes, simply
hold down buttons 1 and 3 until the two green dots
below the house symbol begin to flash.
Fig. 7 Overhead Console With Universal Transmitter
8M - 8 MESSAGE SYSTEMSKJ
COMPASS/MINI-TRIP COMPUTER (Continued)

NOTE: Individual channels cannot be erased. Eras-
ing the transmitter codes will erase ALL pro-
grammed codes.
STANDARD PROCEDURE - SETTING
TRANSMITTER CODES
(1) Turn off the engine.
(2) Erase the factory test codes by pressing but-
tons 1 and 3. Release the buttons when the two
green lights begin to flash (about 20 seconds).
(3) Choose one of the three buttons to train. Place
the hand-held transmitter within one inch of the uni-
versal transmitter and push the buttons on both
transmitters. The green dot below the house symbol
will begin to flash slowly.
(4) When the red light on the universal transmit-
ter begins to flash rapidly (this may take as long as
60 seconds), release both buttons. Your universal
transmitter is now ªtrainedº. To train the other but-
tons, repeat Step 3 and Step 4. Be sure to keep your
hand-held transmitter in case you need to retrain the
universal transmitter.
AMBIENT TEMP SENSOR
DESCRIPTION
Ambient air temperature is monitored by the Com-
pass Mini-Trip Computer (CMTC) through ambient
temperature sensor messages received from the Body
Control Module (BCM) over the Programmable Com-
munications Interface (PCI) data bus network. The
BCM receives a hard wired input from the ambient
temperature sensor. The ambient temperature sensor
(Fig. 8) is a variable resistor mounted in front the
radiator, behind the grille, near the center of the
vehicle.
Refer toBody Control Modulein Electronic Con-
trol Modules. For complete circuit diagrams, refer to
the appropriate wiring information. 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 BCM. The resistance in the sensor
changes as temperature changes, changing the tem-
perature sensor signal circuit voltage to the BCM.
Based upon the resistance in the sensor, the BCM
senses a specific voltage on the temperature sensor
signal circuit, which it is programmed to correspond
to a specific temperature. The BCM then sends the
proper ambient temperature messages to the CMTC
over the PCI data bus.
The thermometer function is supported by the
ambient temperature sensor, a wiring circuit, the
Body Control Module (BCM), the Programmable
Communications Interface (PCI) data bus, and a por-
tion of the Compass Mini-Trip Computer module.
The ambient temperature sensor circuit can also be
diagnosed by referring toDiagnosis and Testing -
Ambient Temperature Sensor, and Diagnosis
and Testing - Ambient Temperature Sensor Cir-
cuit. If the temperature sensor and circuit are con-
firmed to be OK, but the temperature display is
inoperative or incorrect, refer toDiagnosis and
Testing - Compass Mini-Trip Computerin this
section. For complete circuit diagrams, refer to the
appropriate wiring information.
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - AMBIENT
TEMPERATURE SENSOR
(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 (140É F), the sensor
resistance is 2.488 kilohms. The sensor resistance
should read between these two values. If OK, refer to
Diagnosis and Testing - Ambient Temperature
Sensor Circuitin this group. If not OK, replace the
faulty ambient temperature sensor.
DIAGNOSIS AND TESTING - AMBIENT
TEMPERATURE SENSOR CIRCUIT
(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 Body Control Module wire
harness connector.
(2) Connect a jumper wire between the two termi-
nals in the body half of the ambient temperature sen-
sor wire harness connector.
Fig. 8 Ambient Temperature Sensor
KJMESSAGE SYSTEMS 8M - 9
UNIVERSAL TRANSMITTER (Continued)