1994 JEEP CHEROKEE sensor

CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
ON-BOARD DIAGNOSTICS
XJ and YJ models are equipped with On-Board Di-
agnostics for certain cooling system components. Re-
fer to On-Board Diagnostics (OBD) in the Diagnosis
section of this group for additional information. If the
powertrain control module (PCM) detects low engine
coolant temperature, it will record a Diagnostic Trou-
ble Code (DTC) in the PCM memory. The DTC num-
ber for low coolant temperature is 17. Do not change
a thermostat for lack of heat as indicated by the in-
strument panel gauge or heater performance unless a
DTC number 17 is present. Refer to the Diagnosis
section of this group for other probable causes. For
other DTC numbers, refer to On-Board Diagnostics
in the General Diagnosis section of group 14, Fuel
Systems.
The DTC can also be accessed through the DRB
scan tool. Refer to the appropriate Powertrain Diag-
nostic Procedures manual for diagnostic information
and operation of the DRB scan tool.
REMOVAL
WARNING: DO NOT LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRES-
SURIZED. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If the solution
is clean, drain the coolant into a clean container for
reuse.
(1) Drain the coolant from the radiator until the
level is below the thermostat housing.
WARNING: CONSTANT TENSION HOSE CLAMPS
ARE USED ON MOST COOLING SYSTEM HOSES.
WHEN REMOVING OR INSTALLING, USE ONLY
TOOLS DESIGNED FOR SERVICING THIS TYPE OF
CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUM-
BER 6094) (FIG. 14). SNAP-ON CLAMP TOOL (NUM-
BER HPC-20) MAY BE USED FOR LARGER
CLAMPS. ALWAYS WEAR SAFETY GLASSES
WHEN SERVICING CONSTANT TENSION CLAMPS.
CAUTION: A number or letter is stamped into the
tongue of constant tension clamps. If replacement
is necessary, use only an original equipment clamp
with matching number or letter.
(2) Remove radiator upper hose and heater hose at
thermostat housing.
(3) Disconnect wiring connector at engine coolant
temperature sensor.(4) Remove thermostat housing mounting bolts,
thermostat housing, gasket and thermostat (Fig. 15).
Discard old gasket.
(5) Clean the gasket mating surfaces.
INSTALLATION
(1) Install the replacement thermostat so that the
pellet, which is encircled by a coil spring, faces the
engine. All thermostats are marked on the outer
flange to indicate the proper installed position.
(a) Observe the recess groove in the engine cyl-
inder head (Fig. 16).
(b) Position thermostat in groove with arrow and
air bleed hole on outer flange pointing up.
(2) Install replacement gasket and thermostat
housing.
Fig. 14 Hose Clamp ToolÐTypical
Fig. 15 Thermostat Removal/Installation
7 - 14 COOLING SYSTEMJ

CAUTION: Tightening the thermostat housing un-
evenly or with the thermostat out of its recess, may
result in a cracked housing.
(3) Tighten the housing bolts to 20 Nzm (15 ft. lbs.)
torque.
(4) Install hoses to thermostat housing.
(5) Install electrical connector to coolant tempera-
ture sensor.
(6) Be sure that the radiator draincock is tightly
closed. Fill the cooling system to the correct level
with the required coolant mixture. Refer to Refilling
Cooling System in this group.
(7) Start and warm the engine. Check for leaks.
COOLANT
GENERAL INFORMATION
The cooling system is designed around the coolant.
Coolant flows through the engine water jackets ab-
sorbing heat produced during engine operation. The
coolant carries heat to the radiator and heater core.
Here it is transferred to the ambient air passing
through the radiator and heater core fins. The cool-
ant also removes heat from the automatic transmis-
sion fluid in vehicles equipped with an automatic
transmission.
COOLANT PERFORMANCE
The required ethylene-glycol (antifreeze) and water
mixture depends upon climate and vehicle operating
conditions. The coolant performance of various mix-
tures follows:
Pure Water-Water can absorb more heat than a
mixture of water and ethylene-glycol. This is for pur-pose of heat transfer only. Water also freezes at a
higher temperature and allows corrosion.
100 percent Ethylene-Glycol-The corrosion inhib-
iting additives in ethylene-glycol need the presence
of water to dissolve. Without water, additives form
deposits in system. These act as insulation causing
temperature to rise to as high as 149ÉC (300ÉF). This
temperature is hot enough to melt plastic and soften
solder. The increased temperature can result in en-
gine detonation. In addition, 100 percent ethylene-
glycol freezes at -22ÉC (-8ÉF).
50/50 Ethylene-Glycol and Water-Is the recom-
mended mixture, it provides protection against freez-
ing to -37ÉC (-35ÉF). The antifreeze concentration
must alwaysbe a minimum of 44 percent, year-
round in all climates. If percentage is lower, engine
parts may be eroded by cavitation. Maximum protec-
tion against freezing is provided with a 68 percent
antifreeze concentration, which prevents freezing
down to -67.7ÉC (-90ÉF). A higher percentage will
freeze at a warmer temperature. Also, a higher per-
centage of antifreeze can cause the engine to over-
heat because specific heat of antifreeze is lower than
that of water.
CAUTION: Richer antifreeze mixtures cannot be
measured with normal field equipment and can
cause problems associated with 100 percent ethyl-
ene-glycol.
COOLANT SELECTION-ADDITIVES
Coolant should be maintained at the specified level
with a mixture of ethylene glycol-based antifreeze
and low mineral content water. Only use an anti-
freeze containing ALUGARD 340-2 Ÿ.
CAUTION: Do not use coolant additives that are
claimed to improve engine cooling.
COOLANT SERVICE
It is recommended that the cooling system be
drained and flushed at 84,000 kilometers (52,500
miles), or 3 years, whichever occurs first. Then every
two years, or 48,000 kilometers (30,000 miles),
whichever occurs first.
COOLANT LEVEL CHECKÐROUTINE
Do not remove radiator cap for routine coolant
level inspections. The coolant level can be
checked at coolant reserve/overflow tank.
The coolant reserve/overflow system provides a
quick visual method for determining coolant level
without removing radiator pressure cap. With engine
idling and at normal operating temperature, observe
coolant level in reserve/overflow tank. The coolant
level should be between ADD and FULL marks.
Fig. 16 Thermostat Recess
JCOOLING SYSTEM 7 - 15

ADDING ADDITIONAL COOLANTÐROUTINE
Do not remove radiator cap to add coolant to
system.When adding coolant to maintain correct
level, do so at coolant reserve/overflow tank. Use a
50/50 mixture of ethylene-glycol antifreeze contain-
ing Alugard 340-2 Ÿ and low mineral content water.
Remove radiator cap only for testing or when refill-
ing system after service. Removing cap unnecessarily
can cause loss of coolant and allow air to enter sys-
tem, which produces corrosion.
COOLANT LEVEL CHECK-SERVICE
The cooling system is closed and designed to main-
tain coolant level to top of radiator.
WARNING: DO NOT OPEN RADIATOR DRAINCOCK
WITH ENGINE RUNNING OR WHILE ENGINE IS HOT
AND COOLING SYSTEM IS UNDER PRESSURE.
When vehicle servicing requires a coolant level
check in radiator, drain several ounces of coolant
from radiator drain cock. Do this while observing
coolant reserve/overflow system tank. The coolant
level in reserve/overflow tank should drop slightly. If
not, inspect for a leak between radiator and coolant
reserve/overflow system connection. Remove radiator
cap. The coolant level should be to top of radiator. If
not and if coolant level in reserve/overflow tank is at
ADD mark, check for:
²An air leak in coolant reserve/overflow tank or its
hose
²An air leak in radiator filler neck
²Leak in pressure cap seal to radiator filler neck
LOW COOLANT LEVEL-AERATION
If the coolant level in radiator drops below top of
radiator core tubes, air will enter cooling system.
Low coolant level can cause thermostat pellet to be
suspended in air instead of coolant. This will cause
thermostat to open later, which in turn causes higher
coolant temperature. Air trapped in cooling system
also reduces amount of coolant circulating in heater
core resulting in low heat output.
DEAERATION
As the engine operates, any air trapped in cooling
system gathers under the radiator cap. The next time
the engine is operated, thermal expansion of coolant
will push any trapped air past radiator cap into the
coolant reserve/overflow tank. Here it escapes to the
atmosphere into the tank. When the engine cools
down the coolant, it will be drawn from the reserve/
overflow tank into the radiator to replace any re-
moved air.
DRAINING COOLING SYSTEM
ALL MODELSÐEXCEPT XJ WITH 4.0L ENGINE
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If the solution
is clean, drain the coolant into a clean container for
reuse.
DO NOT remove the radiator cap when draining
the coolant from the reserve/overflow tank. Open the
radiator draincock and when the tank is empty, re-
move the radiator cap. The coolant does not have to
be removed from the tank unless the system is being
refilled with a fresh mixture.
(1) Drain the coolant from the radiator by loosen-
ing the draincock.
(2) Drain coolant from engine as follows:
(a) On 2.5L engines (all models) by removing
drain plug at left rear side of block.
(b) On 4.0L engines by removing the drain plug
or coolant temperature sensor on the left side of
the block (Fig. 17).
XJ MODELS WITH 4.0L ENGINE
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM COOLANT
CAN OCCUR.
Fig. 17 Draining CoolantÐ4.0L Engine
7 - 16 COOLING SYSTEMJ

DO NOT WASTE reusable coolant. If the solution
is clean, drain the coolant into a clean container for
reuse.
(1) Remove radiator pressure cap.
(2) For access to radiator draincock, remove radia-
tor grille (Fig. 18).
(3) Attach one end of a 24 inch long X 1/4 inch ID
hose to the radiator draincock. Put the other end into
a clean container. Open draincock and drain coolant
from radiator.
(4) Drain coolant from engine by removing the
drain plug and coolant temperature sensor on left
side of block (Fig. 17).
REFILLING COOLING SYSTEM
YJ MODELS
(1) Remove draining hose. Tighten the radiator
draincock and the cylinder block drain plug(s).
(2) Fill system using a 50/50 mixture of water and
antifreeze. This is described in the Coolant section of
this group. Fill the radiator to the top and install the
radiator cap. Add sufficient coolant to the reserve/
overflow tank to raise the level to the FULL mark.
(3) Operate the engine with the radiator cap and
reserve/overflow tank cap in place. After the engine
has reached the normal operating temperature, shut
the engine off and allow it to cool.
(4) Add coolant to the reserve/overflow tank as
necessary.Only add coolant when the engine is
cold. Coolant level in a warm engine will be
higher due to thermal expansion.
XJ MODELS
(1) Tighten the radiator draincock and the cylinder
block drain plug(s). If removed, install coolant tem-
perature sensor (4.0L engine).
(2) Fill system using a 50/50 mixture of water and
antifreeze as described in the Coolant section of this
group. Fill radiator to top and install radiator cap.
Add sufficient coolant to reserve/overflow tank to
raise level to FULL mark.
(3) With heater control unit in the HEAT position,
operate engine with radiator cap in place.
(4) After engine has reached normal operating
temperature, shut engine off and allow it to cool.
(5) Add coolant to reserve/overflow tank as neces-
sary.Only add coolant when the engine is cold.
Coolant level in a warm engine will be higher
due to thermal expansion.
COOLING SYSTEM CLEANING/REVERSE FLUSHING
CAUTION: The cooling system normally operates at
97-to-124 kPa (14-to-18 psi) pressure. Exceeding
this pressure may damage the radiator or hoses.
CLEANING
Drain cooling system and refill with water. Run
engine with radiator cap installed until upper radia-
tor hose is hot. Stop engine and drain water from
system. If water is dirty, fill system with water, run
engine and drain system. Repeat until water drains
clean.
REVERSE FLUSHING
Reverse flushing of the cooling system is the forc-
ing of water through the cooling system. This is done
using air pressure in the opposite direction of normal
coolant flow. It is usually only necessary with very
dirty systems with evidence of partial plugging.
REVERSE FLUSHING RADIATOR
Disconnect the radiator hoses from the radiator fit-
tings. Attach a section of radiator hose to the radia-
tor bottom outlet fitting and insert the flushing gun.
Connect a water supply hose and air supply hose to
the flushing gun.
CAUTION: The cooling system normally operates at
97-to-124 kPa (14-to-18 psi) pressure. Exceeding
this pressure may damage the radiator or hoses.
Allow the radiator to fill with water. When radia-
tor is filled, apply air in short blasts allowing radia-
tor to refill between blasts. Continue this reverse
flushing until clean water flows out through rear of
radiator cooling tube passages. For more information,
refer to operating instructions supplied with flushing
equipment. Have radiator cleaned more extensively
by a radiator repair shop.
Fig. 18 Draincock AccessÐXJ Models with 4.0L
Engine
JCOOLING SYSTEM 7 - 17

(7) If the voltmeter reading fell below 9.6 volts,
with the battery temperature at a minimum of 70ÉF
(21ÉC), replace the battery.
BATTERY CHARGING
A battery is completely charged when it has:
²an open circuit voltage of 12.4 volts or more.
²has enough cranking capacity (minimum 9.6 volts
when loaded for 15 seconds to 50% of cold crank am-
perage rating at 21ÉC (70ÉF).
An open circuit voltage of 12.4 volts or greater, in-dicates battery is charged enough for further testing
and possible return to use.
WARNING: DO NOT CHARGE A BATTERY THAT
HAS LOW ELECTROLYTE LEVEL. BATTERY MAY
ARC INTERNALLY AND EXPLODE.
WARNING: EXPLOSIVE GASES FORM OVER BAT-
TERY, DO NOT SMOKE, USE FLAME, OR CREATE
SPARKS NEAR BATTERY.
WARNING: DO NOT ASSIST BOOST OR CHARGE A
FROZEN BATTERY, CASING MAY FRACTURE.
WARNING: POISON, CAUSES SEVERE BURNS.
BATTERY CONTAINS SULFURIC ACID, AVOID CON-
TACT WITH SKIN, EYES, OR CLOTHING. IN EVENT
OF CONTACT, FLUSH WITH WATER AND CALL
PHYSICIAN IMMEDIATELY. KEEP OUT OF REACH
OF CHILDREN.
CAUTION: Always disconnect the battery negative
cable before charging battery to avoid damage to
electrical systems. Do not exceed 16.0 volts while
charging battery.
Battery electrolyte will bubble inside case while
being charged properly. If the electrolyte boils or is
discharged from the vent holes while charging, im-
mediately reduce charging rate or turn OFF charger
and evaluate battery condition.
Battery should not be hot to touch.
If the battery feels hot to the touch, turn OFF
charger and let cool before restarting.
Some battery chargers are equipped with polarity
(+ to +/- to -) sensing devices to protect the charger
or battery from being damaged if improperly con-
nected. If the battery state of charge is too low for
the polarity sensor to detect, the sensor must be by-
passed for charger to operate. Refer to operating in-
structions provided with battery charger being used.
Fig. 6 Remove Surface Charge from Battery
Fig. 7 Load 50% Cold Crank Rating Note Voltage
BATTERY CHARGING TIME TABLE
JBATTERY/STARTING/CHARGING SYSTEMS DIAGNOSTICS 8A - 5

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

(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