1994 JEEP CHEROKEE ignition

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

COMPASS REPAIR PROCEDURES
VARIATION ADJUSTMENT PROCEDURE
Variance is the difference between magnetic North
and geographic North. In some areas the difference
between magnetic and geographic north is great
enough to cause the compass to give false readings. If
this occurs, the variance must be set.
To set the variance:
(1) Turn ignition switch to the ON position.
(2) Depress both buttons and holddown until VAR
light appears. This takes about 5 seconds.
(3) Release both buttons.
(4) Using the map (Fig. 1) find your geographic lo-
cation and note the zone number.
(5) Press the U.S./METRIC button to sequentially
go through the numbers until the zone number for
your area appears in the display.
(6) Press the COMP/TEMP button to enter this
zone number.
(7) Confirm correct directions are indicated.
COMPASS CALIBRATION PROCEDURE
CAUTION: DO NOT use magnetic tools when servic-
ing the overhead console.
CAUTION: DO NOT place any external magnets
such as magnetic roof mount antennas, in the vicin-
ity of the compass.
Do not attempt to set compass near large metal ob-
jects such as other vehicles, large buildings or
bridges. The compass features an ``Auto-Cal'' design
which simplifies the calibration procedure. During
normal driving this feature automatically updates
the compass calibration. This takes into account in-
cremental changes in magnetism the vehicle may see
over its lifetime.
Whenever the compass is calibrated manually,
the variation number must also be reset.
Calibrate the compass as follows:
(1) Start the engine.
(2) Depress both buttons on the compass and hold
down until CAL light appears. This takes about 10
seconds and appears about 5 seconds after the VAR
light appears.
(3) Release buttons.
(4) Drive vehicle on a level surface that is away
from metal objects through three or more complete
Fig. 1 Variance Settings
Chart 3
8C - 4 OVERHEAD CONSOLEJ

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

IGNITION SYSTEMS
CONTENTS
page page
COMPONENT IDENTIFICATION/SYSTEM
OPERATION.......................... 1
COMPONENT REMOVAL/INSTALLATION..... 20DIAGNOSTICS/SERVICE PROCEDURES....... 8
IGNITION SWITCH...................... 30
SPECIFICATIONS....................... 33
COMPONENT IDENTIFICATION/SYSTEM OPERATION
INDEX
page page
Automatic Shut Down (ASD) Relay............ 1
Camshaft Position Sensor................... 1
Crankshaft Position Sensor.................. 2
Distributors.............................. 3
Engine Coolant Temperature Sensor........... 4
General Information........................ 1Ignition Coil.............................. 4
Intake Manifold Air Temperature Sensor........ 5
Manifold Absolute Pressure (MAP) Sensor...... 5
Powertrain Control Module (PCM)............. 6
Throttle Position Sensor.................... 6
GENERAL INFORMATION
Throughout this group, references are made to par-
ticular vehicle models by alphabetical designation
(XJ or YJ) or by the particular vehicle nameplate. A
chart showing a breakdown of alphabetical designa-
tions is included in the Introduction group at the be-
ginning of this manual.
This section of the group, Component Identifica-
tion/System Operation, will discuss ignition system
operation and will identify ignition system compo-
nents.
For diagnostic procedures and adjustments, refer to
the Diagnostics/Service Procedures section of this
group.
For removal and installation of ignition system
components, refer to the Component Removal/Instal-
lation section of this group.
For other useful information, refer to On-Board Di-
agnostics in the General Diagnosis sections of Group
14, Fuel System in this manual.
For operation of the DRB Scan Tool, refer to the
appropriate Powertrain Diagnostic Procedures ser-
vice manual.
An Ignition specifications section is included at the
end of this group. A general Maintenance Schedule
(mileage intervals) for ignition related items can be
found in Group 0, Lubrication and Maintenance. This
schedule can also be found in the Owners Manual.
IGNITION SYSTEMS
A multi-port, fuel injected engine is used on all
models. The ignition system is controlled by the Pow-
ertrain Control Module (PCM) on all engines. The
PCM was formerly referred to as the SBEC or engine
controller.
The ignition system consists of:
²Spark Plugs
²Ignition Coil
²Secondary Ignition Cables
²Ignition distributor (contains rotor and camshaft
position sensor)
²Powertrain Control Module (PCM)
²Crankshaft Position Sensor
AUTOMATIC SHUT DOWN (ASD) RELAY
The automatic shut down (ASD) relay is located in
the Power Distribution Center (PDC) near the bat-
tery (Fig. 1 or 2). As one of its functions, it will sup-
ply battery voltage to the ignition coil. The ground
circuit for the ASD relay is controlled by the Power-
train Control Module (PCM). The PCM regulates
ASD relay operation by switching the ground circuit
on-and-off.
CAMSHAFT POSITION SENSOR
The camshaft position sensor is located in the igni-
tion distributor (Figs. 3 or 4) on all engines.
The camshaft position sensor contains a hall effect
device called a sync signal generator to generate a
fuel sync signal. This sync signal generator detects a
JIGNITION SYSTEMS 8D - 1

rotating pulse ring (shutter) on the distributor shaft
(Fig. 4). The pulse ring rotates 180 degrees through
the sync signal generator. Its signal is used in con-
junction with the crankshaft position sensor to differ-
entiate between fuel injection and spark events. It is
also used to synchronize the fuel injectors with their
respective cylinders.
When the leading edge of the pulse ring (shutter)
enters the sync signal generator, the following oc-
curs: The interruption of magnetic field causes the
voltage to switch high resulting in a sync signal of
approximately 5 volts.
When the trailing edge of the pulse ring (shutter)
leaves the sync signal generator, the following oc-
curs: The change of the magnetic field causes the
sync signal voltage to switch low to 0 volts.
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
CRANKSHAFT POSITION SENSOR
The crankshaft position sensor is mounted to the
transmission bellhousing at the left/rear side of the
engine block (Figs. 5, 6 or 7).
Fig. 1 PDCÐXJ Models
Fig. 2 PDCÐYJ Models
Fig. 3 Camshaft Position SensorÐTypical
Fig. 4 DistributorÐTypical
8D - 2 IGNITION SYSTEMSJ

Engine speed and crankshaft position are provided
through the crankshaft position sensor. The sensor
generates pulses that are the input sent to the Pow-
ertrain Control Module (PCM). The PCM interprets
the sensor input to determine the crankshaft posi-
tion. The PCM then uses this position, along with
other inputs, to determine injector sequence and ig-
nition timing.
The sensor is a hall effect device combined with an
internal magnet. It is also sensitive to steel within a
certain distance from it.
SENSOR OPERATION
The flywheel/drive plate has groups of four notches
at its outer edge. On 4.0L 6 cylinder engines there
are three sets of notches (Figs. 9 or 10). On 2.5L 4
cylinder engines there are two sets of notches (Fig.
8).
The notches cause a pulse to be generated when
they pass under the sensor. The pulses are the inputto the PCM. For each engine revolution there are
two groups of four pulses generated on 2.5L 4 cylin-
der engines. There are 3 groups of four pulses gener-
ated on 4.0L 6 cylinder engines.
The trailing edge of the fourth notch, which causes
the pulse, is four degrees before top dead center
(TDC) of the corresponding piston.
The engine will not operate if the PCM does not re-
ceive a crankshaft position sensor input.
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this sensor, refer to
the Component Removal/Installation section of this
group.
DISTRIBUTORS
All engines are equipped with a camshaft driven
mechanical distributor containing a shaft driven dis-
tributor rotor. All distributors are equipped with an
internal camshaft position (fuel sync) sensor. This
sensor provides fuel injection synchronization and
cylinder identification.
The distributors on the 2.5L and 4.0L engines do
not have built in centrifugal or vacuum assisted ad-
vance. Base ignition timing and all timing advance
is controlled by the Powertrain Control Module
(PCM). Because ignition timing is controlled by the
PCM,base ignition timing is not adjustable on
any of these engines.
The distributor is locked in place by a notch on the
distributor housing. The distributor holddown clamp
bolt passes through this notch when installed. Be-
cause the distributor position is locked when in-
Fig. 5 Crankshaft Position SensorÐ2.5L
EngineÐTypical
Fig. 6 Crankshaft Position SensorÐ4.0L EngineÐAll
Except YJ models With Automatic Transmission
Fig. 7 Crankshaft Position SensorÐ4.0L EngineÐYJ
models With Automatic Transmission
JIGNITION SYSTEMS 8D - 3

stalled, its rotational position can not be changed.
Do not attempt to modify the distributor housing
to get distributor rotation. Distributor position
will have no effect on ignition timing.
All distributors contain an internal oil seal that
prevents oil from entering the distributor housing.
The seal is not serviceable.
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
IGNITION COIL
Battery voltage is supplied to the ignition coil pos-
itive terminal from the ASD relay.
The Powertrain Control Module (PCM) opens and
closes the ignition coil ground circuit for ignition coil
operation.
Base ignition timing is not adjustable.By con-
trolling the coil ground circuit, the PCM is able to
set the base timing and adjust the ignition timing
advance. This is done to meet changing engine oper-
ating conditions.
The ignition coil is not oil filled. The windings are
embedded in an epoxy compound. This provides heat
and vibration resistance that allows the ignition coil
to be mounted on the engine.
The ignition coil is mounted to a bracket on the
side of the engine (Fig. 11).
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
ENGINE COOLANT TEMPERATURE SENSOR
The engine coolant temperature sensor provides an
input voltage to the Powertrain Control Module
(PCM) relating coolant temperature. The PCM uses
this input, along with inputs from other sensors, to
determine injector pulse width and ignition timing.
Fig. 8 Sensor OperationÐ2.5L Engine
Fig. 9 Sensor OperationÐ4.0L EngineÐAll Except
YJ Models With Automatic Transmission
Fig. 10 Sensor OperationÐ4.0L EngineÐYJ Models
With Automatic Transmission
8D - 4 IGNITION SYSTEMSJ