front light JEEP CHEROKEE 1994 Service Owner's Manual

4). The engine intake manifold serves as the vacuum
source for booster operation.
The booster is mounted on the engine compartment
side of the dash panel. The master cylinder is
mounted on attaching studs at the front of the
booster. The master cylinder central valves are di-
rectly actuated by the booster push rod.
The pedal travel sensor is mounted in the forward
face of the booster shell. The sensor plunger is actu-
ated by the booster diaphragm plate.
PEDAL TRAVEL SENSOR
The pedal travel sensor signals brake pedal posi-
tion to the antilock ECU. The sensor signal is based
on changes in electrical resistance. The resistance
changes occur in steps that are generated by changes
in brake pedal position. A resistance signal gener-
ated by changing brake pedal position, will cause the
ECU to run the antilock pump when necessary.
The sensor is a plunger-type, electrical switch
mounted in the forward housing of the power brake
booster (Fig. 5). The sensor plunger is actuated by
movement of the booster diaphragm plate.
The tip on the sensor plunger is color coded. The
tip must be matched to the color dot on the face of
the brake booster front shell (Fig. 5).
WHEEL SPEED SENSORS
A sensor is used at each wheel. The sensors convert
wheel speed into an electrical signal. This signal is trans-
mitted to the antilock electronic control unit (ECU).
A gear-type tone ring serves as the trigger mecha-
nism for each sensor. The tone rings are mounted at
the outboard ends of the front and rear axle shafts.
Different sensors are used at the front and rear
wheels (Fig. 6). The front/rear sensors have the same
electrical values but are not interchangeable.
ELECTRONIC CONTROL UNIT (ECU)
A separate electronic control unit (ECU) monitors,
operates and controls the antilock system (Fig. 7).
The ECU contains dual microprocessors. The logic
block in each microprocessor receives identical sensor
signals. These signals are processed and compared si-
multaneously (Fig. 8).
The ECU is located under the instrument panel. It
is located at the right side of the steering column.
The power up voltage source for the ECU is through
the ignition switch in the On and Run positions.
The antilock ECU is separate from the other vehi-
cle electronic control units. It contains a self check
program that illuminates the amber warning light
when a system fault is detected. Faults are stored in
a diagnostic program memory and are accessible
with the DRB II scan tool.
ABS faults remain in memory until cleared, or until af-
ter the vehicle is started approximately 50 times. Stored
faults arenoterased if the battery is disconnected.
ACCELERATION SWITCH
An acceleration switch (Fig. 9), provides an addi-
tional vehicle deceleration reference during 4-wheel
drive operation. The switch is monitored by the anti-
lock ECU at all times.
The switch reference signal is utilized by the ECU
when all wheels are decelerating at the same speed.
Equal wheel speeds occur during braking in undiffer-
entiated 4-wheel ranges.
Fig. 5 Pedal Travel Sensor Location
Fig. 6 Wheel Speed Sensors
JBRAKES 5 - 41

SYSTEM RELAYS
The ABS system has two relays, which are the
main and motor pump relays. The motor pump relay
is used for the motor pump only. The main relay is
used for the solenoid valves and remaining system
components. The main relay is connected to the ECU
at the power control relay terminal.
The pump motor relay starts/stops the pump motor
when signaled by the ECU. The start/stop signal tothe ECU is generated by the pedal travel sensor. Re-
fer to the ABS schematic at the end of this section
for circuit details.
IGNITION SWITCH
The antilock ECU and warning light are in
standby mode with the ignition switch in Off or Ac-
cessory position. No operating voltage is supplied to
the system components.
A 12 volt power feed is supplied to the ECU, re-
lays, solenoid valves, and warning light when the ig-
nition switch is in the ON, Start and Run positions.
Refer to the ABS system schematic at the end of this
section for details.
SYSTEM WARNING LIGHTS
Two warning lights are used. The standard brake
system light is red. The antilock system light is am-
ber. Both lights are in the instrument cluster. The
amber ABS light is in circuit with the ECU and op-
erates independently of the red brake light.
The amber light indicates antilock system condi-
tion. It is in circuit with the valve body solenoids and
main relay. The light illuminates (flashes) at
start-up for the self check. The light then goes out
when the self check program determines system op-
eration is normal.
If an ABS fault occurs either during the start-up
self check, or during normal operation, the amber
light remains on until the fault is corrected.
COMBINATION VALVE
A combination valve is used with the ABS system
(Fig. 2). The valve contains a front/rear brake pres-
sure switch and proportioning valve. The valve is
connected between the master cylinder and hydraulic
control unit (HCU).
Fig. 7 Anti-Lock ECU
Fig. 8 ECU Dual Microprocessor Schematic
Fig. 9 Acceleration Switch
5 - 42 BRAKESJ

ANTILOCK BRAKE SYSTEM OPERATION
INDEX
page page
ABS Operation in Antilock Braking Mode....... 43
ABS Operation in Normal Braking Mode....... 43
Acceleration Switch Operation............... 45
ECY Operation.......................... 46HCU Pump and Pedal Travel Sensor Operation . 44
HCU Solenoid Valve Operation.............. 43
System Power-Up and Initialization........... 43
Wheel Speed Sensor Operation............. 45
SYSTEM POWER-UP AND INITIALIZATION
The antilock system is in standby mode with the
ignition switch in Off or Accessory position. The an-
tilock electrical components are not operational.
Turning the ignition switch to On or Run position
allows battery voltage to flow through the switch to
the ECU ignition terminal.
The ABS system is activated when battery voltage
is supplied to the ECU. The ECU performs a system
initialization procedure at this point. Initialization
consists of a static and dynamic self check of system
electrical components.
The static check occurs immediately after the igni-
tion switch is turned to the On position. The dynamic
check occurs when vehicle road speed reaches ap-
proximately 10 kph (6 mph). During the dynamic
check, the ECU briefly cycles the pump to verify op-
eration. The HCU solenoids are checked continu-
ously.
If an ABS component exhibits a fault during ini-
tialization, the ECU illuminates the amber warning
light and registers a fault code in the microprocessor
memory.
ABS OPERATION IN NORMAL BRAKING MODE
The ECU monitors wheel speed sensor inputs con-
tinuously while the vehicle is in motion. However,
the ECU will not activate any ABS components as
long as sensor inputs and the acceleration switch in-
dicate normal braking.
During normal braking, the master cylinder, power
booster and wheel brake units all function as they
would in a vehicle without ABS. The HCU compo-
nents are not activated.
ABS OPERATION IN ANTILOCK BRAKING MODE
The purpose of the antilock system is to prevent
wheel lockup during periods of high wheel slip. Pre-
venting lockup helps maintain vehicle braking action
and steering control.
The antilock ECU activates the system whenever
sensor signals indicate periods of high wheel slip.
High wheel slip can be described as the point where
wheel rotation begins approaching zero (or lockup)
during braking. Periods of high wheel slip occur
when brake stops involve high pedal pressure and
rate of vehicle deceleration.The antilock system retards lockup during high
slip conditions by modulating fluid apply pressure to
the wheel brake units.
Brake fluid apply pressure is modulated according
to wheel speed, degree of slip and rate of decelera-
tion. A sensor at each wheel converts wheel speed
into electrical signals. These signals are transmitted
to the ECU for processing and determination of
wheel slip and deceleration rate.
The Jeep ABS system has three fluid pressure con-
trol channels. The front brakes are controlled sepa-
rately and the rear brakes in tandem (Fig. 10). A
speed sensor input signal indicating high slip condi-
tions activates the ECU antilock program.
Two solenoid valves are used in each antilock con-
trol channel (Fig. 11). The valves are all located
within the HCU valve body and work in pairs to ei-
ther increase, hold, or decrease apply pressure as
needed in the individual control channels.
The solenoid valves are not static during antilock
braking. They are cycled continuously to modulate
pressure. Solenoid cycle time in antilock mode can be
measured in milliseconds.
HCU SOLENOID VALVE OPERATION
Normal Braking
During normal braking, the HCU solenoid valves
and pump are not activated. The master cylinder and
power booster operate the same as a vehicle without
an ABS brake system.
Antilock Pressure Modulation
Solenoid valve pressure modulation occurs in three
stages which are: pressure increase, pressure hold,
and pressure decrease. The valves are all contained
in the valve body portion of the HCU.
Pressure Decrease
The outlet valve is opened and the inlet valve is
closed during the pressure decrease cycle (Fig. 11).
A pressure decrease cycle is initiated when speed
sensor signals indicate high wheel slip at one or
more wheels. At this point, the ECU opens the outlet
valve. Opening the outlet valve also opens the hy-
draulic return circuit to the master cylinder reser-
JANTILOCK BRAKE SYSTEM OPERATION 5 - 43

(5) Install lever cover. Secure cover with new riv-
ets, or original attaching screws.
(6) Raise vehicle.
(7) Connect tensioner to lever with retaining pin
and E-clip.
(8) Install nuts attaching lever support plate to le-
ver screws.
(9) Adjust parking brakes. Refer to procedure in
this section.
PARKING BRAKE CABLE TENSIONER
REPLACEMENT (XJ)
(1) Raise vehicle.
(2) Remove adjuster nut from tensioner rod. Secure
equalizer and cables to nearby chassis component
with wire.
(3) Remove nuts attaching lever assembly to sup-
port plate and floorpan.
(4) Lower vehicle.
(5) Remove console components and lever assembly
cover.
(6) Remove lever and tensioner assembly.
(7) Move cover and boot for access to tensioner re-
taining pin.
(8) Remove E-clip and pin that attach tensioner to
lever arm (Fig. 3).
(9) Remove tensioner from cover.
(10) Transfer boot to new tensioner if necessary.
(11) Attach tensioner to lever arm with pin and
E-clip.
(12) Verify that E-clip is fully engaged in pin (Fig.
3).(13) Align cover and seal on lever flange.
(14) Verify that tensioner boot is seated in cover
(Fig. 5).
(15) Install assembled lever and tensioner in floor-
pan.
(16) Install necessary console components.
(17) Adjust parking brakes as described in this sec-
tion.
PARKING BRAKE PEDAL REMOVAL (YJ)
(1) Raise vehicle.
(2) Loosen equalizer nuts until front cable is slack
(Fig. 11).
(3) Lower vehicle.
(4) Remove dash-to-instrument panel brace rod, if
equipped.
(5) Disconnect warning light switch wire from
pedal assembly.
(6) On some YJ models, a ground wire may be at-
tached to upper end of bolt that secures parking
brake pedal to instrument panel. Wire is secured
with a nut. Be sure to remove nut and detach ground
wire before proceeding. If this wire is not removed
beforehand, wire and harness could be damaged
when pedal assembly bolt is removed. Ground wire
and attaching nut are accessible from under instru-
ment panel.
(7) Remove bolt securing pedal assembly to instru-
ment panel (Fig. 12).
(8) In engine compartment, remove pedal mount-
ing stud nuts.
(9) Remove pedal assembly from panel.
(10) Disengage front cable from retainer (Fig. 12).
(11) Squeeze cable clip (Fig. 12) and pull cable out
of pedal frame.
(12) Remove pedal assembly.
PARKING BRAKE PEDAL INSTALLATION (YJ)
(1) Connect front cable to pedal retainer.
Fig. 10 Lever Cover (XJ)
Fig. 11 Front Cable And Equalizer (YJ)
JPARKING BRAKES 5 - 61

(2) Position pedal assembly on panel and install
mounting stud nuts and pedal-to-dash bolt.
(3) Install ground wire on upper end of pedal-to-
dash bolt and secure wire with attaching nut.
(4) Connect warning light switch wire to pedal
connector.
(5) Install dash-to-instrument panel brace rod, if
equipped.
(6) Raise vehicle and adjust brake cables. Refer to
procedure in Service Adjustment section.
PARKING BRAKE REAR CABLE REPLACEMENT (XJ)
(1) Raise vehicle and loosen equalizer nuts until
rear cables are slack.
(2) Disengage cable from equalizer and remove ca-
ble clip and spring (Fig. 13).
(3) Remove rear wheel and brake drum.
(4) Remove secondary brakeshoe and disconnect
cable from lever on brakeshoe.
(5) Compress cable retainer with worm drive hose
clamp (Fig. 14) and remove cable from backing plate.
(6) Install new cable in backing plate. Be sure ca-
ble retainer is seated.
(7) Attach cable to lever on brakeshoe and install
brakeshoe on backing plate.
(8) Adjust brakeshoes to drum with brake gauge.
(9) Install brake drum and wheel.
(10) Engage cable in equalizer and install equal-
izer nuts (Fig. 13).
(11) Adjust parking brakes. Refer to procedure in
this section.
PARKING BRAKE FRONT CABLE REPLACEMENT
(YJ)
(1) Raise vehicle.
(2) Remove equalizer nuts (Fig. 15).
(3) Remove front cable from equalizer (Fig. 15).
(4) Remove cable-to-frame bracket clip.
(5) Lower vehicle.(6) Move front carpeting away from pedal.
(7) Compress clip securing cable to pedal frame
(Fig. 15). Use hose clamp to compress clip.
(8) Disconnect cable from pedal retainer and re-
move cable.
(9) Remove grommet (Fig. 15) from old cable and
transfer it to new cable, if necessary.
(10) Install new cable in floorpan and connect it to
pedal assembly.
(11) Seat cable grommet in floorpan.
Fig. 12 Parking Brake Pedal Assembly (YJ)
Fig. 13 Parking Brake Cables (XJ)
Fig. 14 Compressing Rear Cable Retainer
5 - 62 PARKING BRAKESJ

RELEASE BEARING REPLACEMENT
(1) Remove transmission as described in Group 21.
(2) Disconnect release bearing from release lever
and remove bearing (Fig. 5).
(3) Inspect bearing slide surface of transmission
front bearing retainer. Replace retainer if slide sur-
face is scored, worn, or cracked.
(4) Inspect release fork and fork pivot. Be sure
pivot is secure and in good condition. Be sure fork is
not distorted or worn. Replace release fork retainer
spring if bent or damaged in any way.
(5) Lubricate crankshaft pilot bearing with Mopar
high temperature bearing grease. Apply grease to
end of long shank, small diameter flat blade screw-
driver. Then insert tool through clutch disc hub to
reach bearing.
(6) Lubricate input shaft splines, bearing retainer
slide surface, fork pivot and release fork pivot sur-face with Mopar high temperature grease.
(7) Install new release bearing. Be sure bearing is
properly secured to release fork.
(8) Install transmission as described in Group 21.
PILOT BEARING REPLACEMENT
(1) Remove transmission. Refer to Group 21 for
procedure.
(2) Remove clutch cover and disc.
(3) Remove pilot bearing. Use internal (blind hole)
puller such those as supplied in Snap On Tool Set
CG40CB to remove bearing.
(4) Lubricate new bearing with Mopar high tem-
perature bearing grease.
(5) Start new bearing into crankshaft by hand.
Then seat bearing with clutch alignment tool (Fig.
6).
(6) Lightly scuff sand flywheel surface with 180
grit emery cloth. Then clean surface with wax and
grease remover.
(7) Install clutch disc and cover as described in
this section.
(8) Install transmission. Refer to Group 21 for pro-
cedure.
CLUTCH HOUSING REPLACEMENT
The AX 15 clutch housing is removable and can be
replaced when the transmission is out of the vehicle.
The bolts attaching the housing to the transmis-
sion case are located inside the housing (Fig. 7). Rec-
ommended tightening torque for the clutch housing-
to-transmission bolts is 38 Nzm (28 ft. lbs.).
Be sure the transmission and housing mating
surfaces are clean before installing an original,
or replacement clutch housing. Dirt/foreign ma-
terial trapped between the housing and trans-
mission will cause misalignment. If
misalignment is severe enough, the result will be
clutch drag, incomplete release and hard shift-
ing.
CLUTCH HYDRAULIC LINKAGE REMOVAL
The clutch master cylinder, slave cylinder and
connecting line are serviced as an assembly
only. The linkage components cannot be over-
hauled or serviced separately. The cylinders and
connecting line are sealed units. Also note that
removal/installation procedures for right and
left hand drive models are basically the same.
Only master cylinder location is different.
(1) Raise vehicle.
(2) Remove fasteners attaching slave cylinder to
clutch housing.
(3) Remove slave cylinder from clutch housing
(Fig. 8).
(4) Disengage clutch fluid line from body clips.
(5) Lower vehicle.
Fig. 2 Clutch Disc Position
Fig. 3 Typical Method Of Aligning Clutch Disc
JCLUTCH SERVICE 6 - 11

speed of the fan to a predetermined maximum level
at higher engine speeds. A bimetallic spring coil is
located on the front face. This spring coil reacts to
the temperature of the radiator discharge air. It en-
gages the viscous fan drive for higher fan speed if
the air temperature from the radiator rises above a
certain point. Until additional engine cooling is nec-
essary, the fan will remain at a reduced rpm regard-
less of engine speed.
Only when sufficient heat is present, will the vis-
cous fan drive engage. This is when the air flowing
through the radiator core causes a reaction from the
bimetallic coil. It then increases fan speed to provide
the necessary additional engine cooling.
Once the engine has cooled, the radiator discharge
temperature will drop. The bimetallic coil again re-
acts and the fan speed is reduced to the previous dis-
engaged speed.
CAUTION: Engines equipped with serpentine drive
belts have reverse rotating fans and viscous fan
drives. They are marked with the word REVERSE to
designate their usage. Installation of the wrong fan
or viscous fan drive can result in engine overheat-
ing.
VISCOUS FAN DRIVE TEST
The cooling system must be in good condition. This
is checked prior to performing the following test. It
also will ensure against excessively high coolant
temperature.
CAUTION: Be sure that there is adequate fan blade
clearance before drilling.(1) Drill a 3.18-mm (1/8-in) diameter hole in the
top center of the fan shroud.
(2) Obtain a dial thermometer with an 8 inch stem
(or equivalent). It should have a range of -18É-to-
105ÉC (0É-to-220É F). Insert thermometer through the
hole in the shroud. Be sure that there is adequate
clearance from the fan blades.
(3) Connect a tachometer and an engine ignition
timing light (timing light is to be used as a strobe
light).
(4) Block the air flow through the radiator. Secure
a sheet of plastic in front of the radiator (or air con-
ditioner condenser). Use tape at the top to secure the
plastic and be sure that the air flow is blocked.
(5) Be sure that the air conditioner (if equipped) is
turned off.
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN A DI-
RECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR THE PULLEYS, BELTS OR FAN. DO
NOT WEAR LOOSE CLOTHING.
(6) Start the engine and operate at 2400 rpm with
the timing light (strobe light) aimed at the fan
blades. Within ten minutes the air temperature (in-
dicated on the dial thermometer) should be 88É C
(190É F). Satisfactory operation of the fan drive re-
quires that it engage before or at 88É C (190É F). En-
gagement is distinguishable by a definite increase in
flow noise. The timing light also will indicate an in-
crease in the speed of the fan.
(7) When the air temperature reaches 88É C (190É
F), remove the plastic sheet. Satisfactory operation of
the viscous fan requires the air temperature to drop
20É F (11É C) or more. A definite decrease of audible-
fan-air-flow-noise should be noticed. Replace defec-
tive fan assemblies.
VISCOUS FAN DRIVE REPLACEMENT
REMOVAL
Some engines have the mechanical fan/viscous fan
drive assembly mounted directly to the water pump
hub (Fig. 38). It may also be mounted to a hub/bear-
ing attached to an aluminum bracket on the right
front side of engine (Fig. 39).
(1) Loosen but do not remove at this time, the four
fan hub mounting nuts (Figs. 38 or 39).
(2) Remove accessory serpentine drive belt. Refer
to Belt Service in the Engine Accessory Drive Belt
section of this group.
(3) Some models with certain engines may require
the removal of the fan shroud to remove the viscous
fan drive. The fan shroud and fan blade/viscous fan
drive should be removed from the vehicle as one as-
sembly.
Fig. 37 Viscous Fan DriveÐTypical
JCOOLING SYSTEM 7 - 27

OVERHEAD CONSOLE
CONTENTS
page page
COMPASS REPAIR PROCEDURES.......... 4
CONSOLE REPAIR PROCEDURES........... 6
DESCRIPTION........................... 1DIAGNOSTIC PROCEDURES............... 1
THERMOMETER AND SENSOR SYSTEM REPAIR
PROCEDURES......................... 6
DESCRIPTION
The overhead console includes:
²a compass/temperature display
²reading and courtesy lights for the front and rear
seats
²the receiver for the keyless entry system
²storage compartment for remote garage door
opener
²storage compartment for sunglasses.
COMPASS
The compass will display the direction the vehicle
is pointed, using the eight major compass headings
(Examples: North is ``N'', Northeast is ``NE''). It does
not display the headings in actual degrees. The dis-
play is turned on/off using the TEMP/COMP button
on the left of the display.
The compass is a self calibrating unit that should
not require recalibration. The only calibration that
may prove necessary is to drive the vehicle in 3 com-
plete circles, on level ground, in not less than 48 sec-
onds. This will ``reorient'' the unit to its vehicle. The
unit also will compensate for magnetism the vehicle
may acquire during its life. Care should be used to
avoid putting anything magnetic on the roof of the
vehicle.
The unit can compensate for some magnetic fields
in the body. The use of magnetic attachments like
antenna mounts or repair order ``hats'' placed di-
rectly on the roof can exceed the compensation abil-
ity of the unit. Magnetic bit drivers used on the
fasteners to hold the assembly to the roof header can
also affect operation. If the vehicle roof should be-
come magnetized, then the degaussing and calibra-
tion procedures may be required to restore proper
operation.
If the compass functions but accuracy is suspect, it
may be necessary to perform a variation adjustment.
This procedure allows the unit to accommodate vari-
ations in the earth's magnetic field strength based on
geographic location.
If the compass has blanked out and only CAL
appears, degaussing may be necessary to re-
move residual magnetic fields.
THERMOMETER
The ambient temperature display can be changed
from Fahrenheit to Celsius using the U.S./METRIC
button on the right of the display. The temperature
reported is not an instant reading of conditions but
an average temperature. It may take the unit several
minutes to react to a major change such as driving
out of a heated garage into winter temperatures.
When the ignition switch is turned OFF, the last
displayed temperature reading stays in memory.
When the ignition switch is turned ON again the
thermometer will display the memory temperature
for one minute; then update the display to the actual
temperature within five minutes.
READING AND COURTESY LAMPS
All reading and courtesy lamps in the overhead
console are activated by the door courtesy circuit.
When all four doors and the liftgate are closed the
lamps can be activated by depressing the correspond-
ing lens. When any door or the liftgate is open, the
switches are disabled. They will not turn the lamps
off.
MAP AND COURTESY LAMPS
These lamps offer several unique features. Both the
map and courtesy lamps can be turned on with the
integral ``Soft Touch'' switch. Pushing this switch en-
ergizes an electrical circuit, which in turn directs
power to the light. The map lamps are unaffected by
the door switches, while the courtesy lamps are
turned on with the opening of any door. When any
door is open, the ``Soft Touch'' switches are disabled,
you cannot turn the lights off with these switches.
DIAGNOSTIC PROCEDURES
Follow the appropriate diagnostic flow chart:
²Chart 1 describes the procedures for compass and
display problems.
²Chart 2 describes the procedures for illumination
lamp problems.
²Chart 3 describes the procedures for outside tem-
perature measuring problems.
JOVERHEAD CONSOLE 8C - 1

circles, in not less than 48 seconds. The CAL light
will go off and the compass is now calibrated.
(5) Reset variation number. This step must be
done every time step 2 is performed.
If CAL light does not go off, either there is ex-
cessive magnetism near the compass or the unit
is defective. Repeat the degaussing and calibra-
tion procedures at least one more time.
If the wrong direction is still indicated, the
area selected may be too close to a magnetic
source. Repeat the calibration procedure in an-
other location.
DEGAUSSING PROCEDURE
The tool used to degauss or demagnetize the forward
console attaching screw and roof panel is the Miller
Tool 6029. Equivalent units must be rated as continu-
ous duty for 110/115 volts, 60Hz with a field strength of
over 350 gauss at 1/4 inch beyond the tip of the probe.
In this degaussing procedure the degaussing tool is
used to demagnetize both the roof panel and console
forward mounting screw.
(1) Be sure the ignition switch is in the OFF posi-
tion before you begin the degaussing procedures.
CAUTION: Keep the degaussing tool at least 2 inches
away from the compass area when plugging it in.
(2) Plug the degaussing tool into a standard
110/115 volt AC outlet.
CONSOLE FORWARD MOUNTING SCREW
(3) Slowly approach the head of the forward
mounting screw with the plastic coated tip of the de-
gaussing tool. Contact the head of the screw for
about two seconds.
(4) With the degaussing tool still energized, slowly
back it away from the screw until the tool is at least
2 inches from the screw head then unplug the tool.
ROOF PANEL
(5) Place an 8 1/2 X 11 piece of paper on the center
of the roof at the windshield, oriented lengthwise
from front to rear. The purpose of the paper is pro-
tect the roof panel from scratches and define the area
to be degaussed (Fig. 2). Figure 2 shows the recom-
mended sweep pattern of 1/2 inch between passes in
a sweeping zig-zag pattern.
(6) Plug in the degaussing tool. Keep the tool at
least 2 inches away from the compass unit.
(7) Slowly approach the center of the roof panel at
the windshield with the degaussing tool plugged in.
(8) Contact the roof panel with the tip of the tool
(be sure template is in place to avoid scratching the
roof panel). Using slow sweeping motions of 1/2 inch
between sweeps, move the tool approximately 49ei-
ther side of the centerline and at least 11 inches
back from the windshield.(9) With the degaussing tool still energized, slowly
back it away from the roof panel until the tip is at
least 2 inches from the roof then unplug the tool.
(10) Calibrate the compass and set the variance as
described.
SELF-DIAGNOSTIC TEST
The self-diagnostic test is used to verify the com-
pass is working properly electrically. This can be
used to confirm that the display and all of its seg-
ments are operating properly. Initiate the self-diag-
nostic test as follows:
(1) With the ignition switch in the OFF position si-
multaneously press and hold the COMP/TEMP but-
ton and the US/METRIC button.
(2) Turn ignition switch to ON.
(3) Continue to hold both buttons until the display
performs a walking segment test. In this test all of
the compass points are displayed along with various
number combinations. These combinations verify
that all segments work. To repeat the test, press the
COMP/TEMP button.
(4) Press the US/METRIC button, and all segments
will light simultaneously for about 2 seconds. To re-
peat the test, press the COMP/TEMP button.
(5) Press the US/METRIC button to return to nor-
mal operation.
Fig. 2 Roof Degaussing Pattern
JOVERHEAD CONSOLE 8C - 5

(6) Should any segment in any of the digit positions
fail to light, the unit is defective and should be re-
placed.
THERMOMETER AND SENSOR SYSTEM REPAIR
PROCEDURES
This portion of the display consists of a sensor, the
circuit and display devoted to the temperature mea-
suring and display. The sensor is mounted at the
center of the vehicle below the grille, behind the
front bumper (Fig. 3).
If an electrical component breaks it will diagnose as
an open or short circuit. The system reports SC when
the sensor is exposed to temperatures in excess of 140ÉF
or if the circuit is shorted. If the temperature is below
-40ÉF or an open exists, the system will display OC.
To diagnose the temperature sensor perform the
following procedures. If the sensor and wiring are
OK then the electronic module is defective and
should be replaced.
SENSOR TEST
(1) Turn the ignition switch to OFF.
(2) Measure resistance of sensor. At -40ÉF the re-
sistance is 336K ohms. At 140ÉF the resistance is
2.488K ohms. If resistance is NOT between these two
values, then the sensor is faulty. Replace the sensor.CIRCUIT TEST
(1) Locate temperature sensor and disconnect har-
ness connector.
(2) Short the pins on the harness connector by us-
ing a jumper wire.
(3) Remove the overhead console as described in
Console Repair Procedures.
(4) Check continuity between pins 10 and 11 of
compass/temperature harness connector (Fig. 4). If an
open circuit is detected, repair as required.
(5) Remove jumper wire on temperature sensor
harness connector. Check continuity between pins 10
and 11 of compass/temperature harness connector
(Fig. 4). If a short is detected, repair as required.
CONSOLE REPAIR PROCEDURES
(1) Remove screw forward of the compass unit (Fig.
5).
(2) Flex housing outward while pressing upward to
disengage the housing from the rear bracket (arrow 1)
(Fig. 5).
Fig. 4 Compass/Temperature Harness Connector
Fig. 5 Remove/Install Overhead Console
Fig. 3 Temperature Sensor Viewed From
Underneath Vehicle
8C - 6 OVERHEAD CONSOLEJ