2002 JEEP GRAND CHEROKEE Group 8W

(2) Insert block heater assembly with element loop
pointing at twelve o'clock (Fig. 19).
(3) With block heater fully seated, tighten center
screw to 2 N´m (17 in. lbs.) torque.
(4) Refill cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE).
(5) Start and warm the engine. Check for leaks.
ENGINE COOLANT TEMP
SENSOR
DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is
used to sense engine coolant temperature. The sensor
protrudes into an engine water jacket.
The ECT sensor is a two-wire Negative Thermal
Coefficient (NTC) sensor. Meaning, as engine coolant
temperature increases, resistance (voltage) in the
sensor decreases. As temperature decreases, resis-
tance (voltage) in the sensor increases.
OPERATION
At key-on, the Powertrain Control Module (PCM)
sends out a regulated 5 volt signal to the ECT sensor.
The PCM then monitors the signal as it passes
through the ECT sensor to the sensor ground (sensor
return).
When the engine is cold, the PCM will operate in
Open Loop cycle. It will demand slightly richer air-
fuel mixtures and higher idle speeds. This is done
until normal operating temperatures are reached.
The PCM uses inputs from the ECT sensor for the
following calculations:
²for engine coolant temperature gauge operation
through CCD or PCI (J1850) communications
²Injector pulse-width
²Spark-advance curves
²ASD relay shut-down times
²Idle Air Control (IAC) motor key-on steps
²Pulse-width prime-shot during cranking
²O2 sensor closed loop times
²Purge solenoid on/off times
²EGR solenoid on/off times (if equipped)
²Leak Detection Pump operation (if equipped)
²Radiator fan relay on/off times (if equipped)
²Target idle speed
REMOVAL
REMOVALÐ4.0L ENGINE
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. COOLING SYSTEM
MUST BE PARTIALLY DRAINED BEFORE REMOV-
ING THE ENGINE COOLANT TEMPERATURE (ECT)
SENSOR. REFER TO GROUP 7, COOLING.
(1) Partially drain cooling system. (Refer to 7 -
COOLING - STANDARD PROCEDURE).
Fig. 18 Drain Plug
1 - COOLANT TEMPERATURE SENSOR
2 - BLOCK DRAIN PLUG
Fig. 19 Engine Block Heater
1 - ENGINE BLOCK HEATER
WJENGINE 7 - 35
ENGINE BLOCK HEATER (Continued)

(2) Disconnect electrical connector from ECT sen-
sor (Fig. 20).
(3) Remove sensor from thermostat housing.
REMOVALÐ4.7L ENGINE
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. COOLING SYSTEM
MUST BE PARTIALLY DRAINED BEFORE REMOV-
ING THE ENGINE COOLANT TEMPERATURE (ECT)
SENSOR. REFER TO GROUP 7, COOLING.
The ECT sensor is located near the front of the
intake manifold (Fig. 21).
(1) Partially drain cooling system. (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(2) Disconnect electrical connector from ECT sen-
sor.
(3) Remove sensor from intake manifold.
INSTALLATION
INSTALLATIONÐ4.0L ENGINE
(1) Install sensor.
(2) Tighten to 11 N´m (8 ft. lbs.) torque.
(3) Connect electrical connector to sensor.
(4) Replace any lost engine coolant. (Refer to 7 -
COOLING - STANDARD PROCEDURE).
INSTALLATIONÐ4.7L ENGINE
(1) Install sensor.
(2) Tighten to 11 N´m (8 ft. lbs.) torque.
(3) Connect electrical connector to sensor.
(4) Replace any lost engine coolant. (Refer to 7 -
COOLING - STANDARD PROCEDURE).
ENGINE COOLANT
THERMOSTAT
DESCRIPTION
DESCRIPTIONÐ4.7L ENGINE
CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
A pellet-type thermostat controls the operating
temperature of the engine by controlling the amount
of coolant flow to the radiator. On all engines the
thermostat is closed below 195ÉF (90ÉC). Above this
temperature, coolant is allowed to flow to the radia-
tor. This provides quick engine warm up and overall
temperature control. On the 4.7L engine the thermo-
stat is designed to block the flow of the coolant
bypass journal by 50% instead of completely blocking
the flow. This design controls coolant temperature
more accurately (Fig. 22).
Fig. 20 Engine Coolant Temperature Sensor
1 - THERMOSTAT HOUSING
2 - ENGINE COOLANT TEMPERATURE SENSOR
3 - ELECTRICAL CONNECTOR
Fig. 21 Engine Coolant Temperature Sensor
1 - ECT SENSOR
2 - MOUNTING BOLTS (2)
3 - MAP SENSOR
4 - INTAKE MANIFOLD
7 - 36 ENGINEWJ
ENGINE COOLANT TEMP SENSOR (Continued)

(9) Disconnect the overflow hose from radiator
(Fig. 41).
(10) Remove the air inlet duct at the grill.
(11) The lower part of radiator is equipped with
two alignment dowel pins (Fig. 40). They are located
on the bottom of radiator tank and fit into rubber
grommets. These rubber grommets are pressed into
the radiator lower crossmember.
WARNING: THE AIR CONDITIONING SYSTEM (IF
EQUIPPED) IS UNDER A CONSTANT PRESSURE
EVEN WITH THE ENGINE OFF. REFER TO REFRIG-
ERANT WARNINGS IN GROUP 24, HEATING AND
AIR CONDITIONING BEFORE HANDLING ANY AIR
CONDITIONING COMPONENT.
(12) If equipped with an auxiliary automatic trans-
mission oil cooler, use caution when removing radia-
tor. The oil cooler lines are routed through a rubber
air seal on the right side of radiator. Do not cut or
tear this seal.
(13) Gently lift up and remove radiator from vehi-
cle. Be careful not to scrape the radiator fins against
any other component. Also be careful not to disturb
the air conditioning condenser (if equipped).
CLEANING
Clean radiator fins With the engine cold, apply cold
water and compressed air to the back (engine side) of
the radiator to flush the radiator and/or A/C con-
denser of debris.
Fig. 39 Air Seals - Typical
1 - AIR DAM
2 - RADIATOR
3 - AIR DAM
4 - A/C CONDENSER
5 - AIR SEAL
Fig. 40 Radiator Alignment Dowels
1 - RADIATOR
2 - ALIGNMENT DOWEL
3 - RADIATOR LOWER ISOLATOR
4 - RADIATOR LOWER CROSSMEMBER
Fig. 41 Radiator, Shroud and Electric Fan
1 - RADIATOR/SHROUD/FAN ASSEMBLY
2 - OVER FLOW HOSE
3 - ELECTRIC FAN CONNECTOR
4 - RADIATOR MOUNTING BOLT(S)
5 - CLAMP
7 - 46 ENGINEWJ
RADIATOR - 4.0L (Continued)

CAUTION: When installing the serpentine engine
accessory drive belt, the belt MUST be routed cor-
rectly. If not, the engine may overheat due to the
water pump rotating in the wrong direction. Refer to
the Belt Removal and Installtion in this group for
appropriate belt routing. You may also refer to the
Belt Routing Label in the vehicle engine compart-
ment.
Install accessory drive belt (Refer to 7 - COOLING/
ACCESSORY DRIVE/DRIVE BELTS - INSTALLA-
TION).
(6) Install fan blade and viscous fan drive onto
water pump.
(7) Fill cooling system with coolant and check for
leaks. (Refer to 7 - COOLING - STANDARD PROCE-
DURE).
(8) Connect battery cable to battery.
(9) Start and warm the engine. Check for leaks.
RADIATOR PRESSURE CAP
DESCRIPTION
All radiators are equipped with a pressure cap
(Fig. 50). This cap releases pressure at some point
within a range of 124-to-145 kPa (18-to-21 psi). The
pressure relief point (in pounds) is engraved on top of
the cap
The cooling system will operate at pressures
slightly above atmospheric pressure. This results in a
higher coolant boiling point allowing increased radi-
ator cooling capacity. The cap contains a spring-
loaded pressure relief valve. This valve opens when
system pressure reaches the release range of 124-to-
145 kPa (18-to-21 psi).
A rubber gasket seals the radiator filler neck. This is
done to maintain vacuum during coolant cool-down and
to prevent leakage when system is under pressure.
OPERATION
A vent valve in the center of the cap will remain
shut as long as the cooling system is pressurized. As
the coolant cools, it contracts and creates a vacuum
in cooling system. This causes the vacuum valve to
open and coolant in reserve/overflow tank to be
drawn through connecting hose into radiator. If the
vacuum valve is stuck shut, or overflow hose is
kinked, radiator hoses will collapse on cool-down.
DIAGNOSIS AND TESTINGÐRADIATOR
PRESSURE CAP
Remove cap from radiator. Be sure that sealing
surfaces are clean. Moisten rubber gasket with water
and install the cap on pressure tester (tool 7700 or
an equivalent) (Fig. 51).Operate the tester pump and observe the gauge
pointer at its highest point. The cap release pressure
should be 124 to 145 kPa (18 to 21 psi). The cap is
satisfactory when the pressure holds steady. It is also
good if it holds pressure within the 124 to 145 kPa
(18 to 21 psi) range for 30 seconds or more. If the
pointer drops quickly, replace the cap.
CAUTION: Radiator pressure testing tools are very
sensitive to small air leaks, which will not cause
cooling system problems. A pressure cap that does
not have a history of coolant loss should not be
replaced just because it leaks slowly when tested
with this tool. Add water to tool. Turn tool upside
down and recheck pressure cap to confirm that cap
needs replacement.CLEANING
Clean the radiator pressure cap using a mild soap
and water only.
Fig. 50 Radiator Pressure Cap - Typical
1 - FILLER NECK SEAL
2 - VACUUM VENT VALVE
3 - PRESSURE RATING
4 - PRESSURE VALVE
WJENGINE 7 - 53
WATER PUMP - 4.0L (Continued)

CONDITION POSSIBLE CAUSES CORRECTION
POOR RADIO RECEPTION 1. Antenna faulty. 1. (Refer to 8 - ELECTRICAL/AUDIO/ANTENNA
BODY & CABLE - DIAGNOSIS AND TESTING).
2. Radio ground faulty. 2. Check for continuity between radio chassis and
a known good ground. There should be
continuity. Repair ground, if required.
3. Radio noise suppression
faulty.3. (Refer to 8 - ELECTRICAL/AUDIO/RADIO
NOISE SUPPRESSION - DIAGNOSIS AND
TESTING).
4. Radio faulty. 4. (Refer to 8 - ELECTRICAL/AUDIO/RADIO -
DIAGNOSIS AND TESTING).
NO/POOR TAPE
OPERATION1. Faulty tape. 1. Insert known good tape and test operation.
2. Foreign objects behind
tape door.2. Remove foreign objects and test operation.
3. Dirty cassette tape head. 3. Clean head with Mopar Cassette Head
Cleaner.
4. Faulty tape deck. 4. Exchange or replace radio, if required.
NO COMPACT DISC
OPERATION, OR CD
SKIPPING SOUND1. Faulty CD. 1. Insert known good CD and test operation.
2. Foreign material on CD. 2. Clean CD and test operation.
3. Condensation on CD or
optics.3. Allow temperature of vehicle interior to stabilize
and test operation.
4. Faulty CD player. 4. Exchange or replace radio, if required.
NO COMPACT DISC
CHANGER OPERATION, OR
CD SKIPPING SOUND1. Faulty CD. 1. Insert known good CD and test operation.
2. Foreign material on CD. 2. Clean CD and test operation.
3. Condensation on CD or
optics.3. Allow temperature of vehicle interior to stabilize
and test operation.
4. CD changer connector
faulty.4. Check for loose or corroded CD changer
connections. Repair, if required.
5. Wiring faulty. 5. Refer to Compact Disc Changer in the
Diagnosis and Testing section of this group.
6. PCI data bus faulty. 6. Use DRB scan tool and the Diagnostic
Procedures manual to test PCI data bus. Repair,
if required.
7. CD changer faulty. 7. Refer to Compact Disc Changer in the
Diagnosis and Testing section of this group.
WJAUDIO 8A - 5
AUDIO (Continued)

INSPECTION
The following information details the recommended
inspection procedures for the battery and related
components. In addition to the maintenance sched-
ules found in this service manual and the owner's
manual, it is recommended that these procedures be
performed any time the battery or related compo-
nents must be removed for vehicle service.
(1) Inspect the battery cable terminal clamps for
damage. Replace any battery cable that has a dam-
aged or deformed terminal clamp.
(2) Inspect the battery tray and battery holddown
hardware for damage. Replace any damaged parts.
(3) Slide the thermal guard off of the battery case.
Inspect the battery case for cracks or other damage
that could result in electrolyte leaks. Also, check the
battery terminal posts for looseness. Batteries with
damaged cases or loose terminal posts must be
replaced.
(4) Inspect the battery built-in test indicator sight
glass for an indication of the battery condition. If the
battery is discharged, charge as required. Refer to
Standard Procedures for the proper battery built-in
indicator test procedures. Also refer to Standard Pro-
cedures for the proper battery charging procedures.
SPECIFICATIONS
The battery Group Size number, the Cold Cranking
Amperage (CCA) rating, and the Reserve Capacity
(RC) rating or Ampere-Hours (AH) rating can be
found on the original equipment battery label. Be
certain that a replacement battery has the correct
Group Size number, as well as CCA, and RC or AH
ratings that equal or exceed the original equipment
specification for the vehicle being serviced. Battery
sizes and ratings are discussed in more detail below.
²Group Size- The outside dimensions and ter-
minal placement of the battery conform to standards
established by the Battery Council International
(BCI). Each battery is assigned a BCI Group Size
number to help identify a correctly-sized replace-
ment.
²Cold Cranking Amperage- The Cold Crank-
ing Amperage (CCA) rating specifies how much cur-
rent (in amperes) the battery can deliver for thirty
seconds at -18É C (0É F). Terminal voltage must not
fall below 7.2 volts during or after the thirty second
discharge period. The CCA required is generally
higher as engine displacement increases, depending
also upon the starter current draw requirements.
²Reserve Capacity- The Reserve Capacity (RC)
rating specifies the time (in minutes) it takes for bat-
tery terminal voltage to fall below 10.5 volts, at a
discharge rate of 25 amperes. RC is determined with
the battery fully-charged at 26.7É C (80É F). This rat-
ing estimates how long the battery might last after a
charging system failure, under minimum electrical
load.
²Ampere-Hours- The Ampere-Hours (AH) rat-
ing specifies the current (in amperes) that a battery
can deliver steadily for twenty hours, with the volt-
age in the battery not falling below 10.5 volts. This
rating is also sometimes identified as the twenty-
hour discharge rating.
BATTERY CLASSIFICATIONS & RATINGS
Part NumberBCI Group Size
ClassificationCold Cranking
AmperageReserve
CapacityAmpere -
HoursLoad Test
Amperage
56041113 65 625 120 Minutes 69 300
8F - 6 BATTERY SYSTEMWJ
BATTERY SYSTEM (Continued)

SPECIAL TOOLS
BATTERY
DESCRIPTION
A large capacity, low-maintenance storage battery
(Fig. 4) is standard factory-installed equipment on
this model. Male post type terminals made of a soft
lead material protrude from the top of the molded
plastic battery case to provide the means for connect-
ing the battery to the vehicle electrical system. The
battery positive terminal post is visibly larger in
diameter than the negative terminal post, for easy
identification. The lettersPOSandNEGare also
molded into the top of the battery case adjacent to
their respective positive and negative terminal posts
for additional identification confirmation. Refer to
Battery Cablesin the index of this service manual
for the location of more information on the battery
cables that connect the battery to the vehicle electri-
cal system.
This battery is designed to provide a safe, efficient
and reliable means of storing electrical energy in a
chemical form. This means of energy storage allows
the battery to produce the electrical energy required
to operate the engine starting system, as well as to
operate many of the other vehicle accessory systems
for limited durations while the engine and/or the
charging system are not operating. The battery is
made up of six individual cells that are connected in
series. Each cell contains positively charged plate
groups that are connected with lead straps to thepositive terminal post, and negatively charged plate
groups that are connected with lead straps to the
negative terminal post. Each plate consists of a stiff
mesh framework or grid coated with lead dioxide
(positive plate) or sponge lead (negative plate). Insu-
lators or plate separators made of a non-conductive
material are inserted between the positive and nega-
tive plates to prevent them from contacting or short-
ing against one another. These dissimilar metal
plates are submerged in a sulfuric acid and water
solution called an electrolyte.
Some factory-installed batteries have a built-in test
indicator (hydrometer). The color visible in the sight
glass of the indicator will reveal the battery condi-
tion. For more information on the use of the built-in
test indicator, refer toStandard Procedures The
factory-installed low-maintenance battery has
removable battery cell caps.Distilled water can
be added to this battery. The battery is not sealed
and has vent holes in the cell caps. The chemical
composition of the metal coated plates within the
low-maintenance battery reduces battery gassing and
water loss, at normal charge and discharge rates.
Therefore, the battery should not require additional
water in normal service. If the electrolyte level in
this battery does become low, distilled water must be
added. However, rapid loss of electrolyte can be
caused by an overcharging condition. Be certain to
MICRO 420 BATTERY AND CHARGING SYSTEM
TESTER
Fig. 4 Low-Maintenance Battery - Typical
1 - POSITIVE POST
2 - VENT
3 - CELL CAP
4 - TEST INDICATOR
5 - CELL CAP
6 - VENT
7 - NEGATIVE POST
8 - GREEN BALL
9 - ELECTROLYTE LEVEL
10 - PLATE GROUPS
11 - LOW-MAINTENANCE BATTERY
WJBATTERY SYSTEM 8F - 7
BATTERY SYSTEM (Continued)

diagnose the charging system after replenishing the
water in the battery for a low electrolyte condition
and before returning the vehicle to service. Refer to
Charging Systemfor additional information.
For battery maintenance schedules and jump start-
ing procedures, see the owner's manual in the vehicle
glove box. Optionally, refer toMaintenance Sched-
ulesandJump Starting, Towing and Hoistingin
the index of this service manual for the location of
the recommended battery maintenance schedules and
the proper battery jump starting procedures. While
battery charging can be considered a maintenance
procedure, the battery charging procedures and infor-
mation are located in the service procedures section
of this service manual. This was done because the
battery must be fully-charged before any battery
diagnosis or testing procedures can be performed.
Refer toStandard Proceduresin the index of this
service manual for the location of the proper battery
charging procedures.
OPERATION
The battery is designed to store electrical energy in
a chemical form. When an electrical load is applied to
the terminals of the battery, an electrochemical reac-
tion occurs. This reaction causes the battery to dis-
charge electrical current from its terminals. As the
battery discharges, a gradual chemical change takes
place within each cell. The sulfuric acid in the elec-
trolyte combines with the plate materials, causing
both plates to slowly change to lead sulfate. At the
same time, oxygen from the positive plate material
combines with hydrogen from the sulfuric acid, caus-
ing the electrolyte to become mainly water. The
chemical changes within the battery are caused by
the movement of excess or free electrons between the
positive and negative plate groups. This movement of
electrons produces a flow of electrical current
through the load device attached to the battery ter-
minals.
As the plate materials become more similar chem-
ically, and the electrolyte becomes less acid, the volt-
age potential of each cell is reduced. However, by
charging the battery with a voltage higher than that
of the battery itself, the battery discharging process
is reversed. Charging the battery gradually changes
the sulfated lead plates back into sponge lead and
lead dioxide, and the water back into sulfuric acid.
This action restores the difference in the electron
charges deposited on the plates, and the voltage
potential of the battery cells. For a battery to remain
useful, it must be able to produce high-amperage cur-
rent over an extended period. A battery must also be
able to accept a charge, so that its voltage potential
may be restored.The battery is vented to release excess hydrogen
gas that is created when the battery is being charged
or discharged. However, even with these vents,
hydrogen gas can collect in or around the battery. If
hydrogen gas is exposed to flame or sparks, it may
ignite. If the electrolyte level is low, the battery may
arc internally and explode. If the battery is equipped
with removable cell caps, add distilled water when-
ever the electrolyte level is below the top of the
plates. If the battery cell caps cannot be removed, the
battery must be replaced if the electrolyte level
becomes low.
DIAGNOSIS AND TESTING - BATTERY
The battery must be completely charged and the
terminals should be properly cleaned and inspected
before diagnostic procedures are performed. Refer to
Battery System Cleaning for the proper cleaning pro-
cedures, and Battery System Inspection for the
proper battery inspection procedures. Refer to Stan-
dard Procedures for the proper battery charging pro-
cedures.
MICRO 420 ELECTRICAL SYSTEM TESTER
The Micro420 automotive battery tester is designed
to help the dealership technicians diagnose the cause
of a defective battery. Follow the instruction manual
supplied with the tester to properly diagnose a vehi-
cle. If the instruction manual is not available refer to
the standard procedure in this section, which
includes the directions for using the Micro420 electri-
cal system tester.
WARNING: IF THE BATTERY SHOWS SIGNS OF
FREEZING, LEAKING OR LOOSE POSTS, DO NOT
TEST, ASSIST-BOOST, OR CHARGE. THE BATTERY
MAY ARC INTERNALLY AND EXPLODE. PERSONAL
INJURY AND/OR VEHICLE DAMAGE MAY RESULT.
WARNING: EXPLOSIVE HYDROGEN GAS FORMS IN
AND AROUND THE BATTERY. DO NOT SMOKE,
USE FLAME, OR CREATE SPARKS NEAR THE BAT-
TERY. PERSONAL INJURY AND/OR VEHICLE DAM-
AGE MAY RESULT.
WARNING: THE BATTERY CONTAINS SULFURIC
ACID, WHICH IS POISONOUS AND CAUSTIC. AVOID
CONTACT WITH THE SKIN, EYES, OR CLOTHING.
IN THE EVENT OF CONTACT, FLUSH WITH WATER
AND CALL A PHYSICIAN IMMEDIATELY. KEEP OUT
OF THE REACH OF CHILDREN.
A battery that will not accept a charge is faulty,
and must be replaced. Further testing is not
required. A fully-charged battery must be load tested
8F - 8 BATTERY SYSTEMWJ
BATTERY (Continued)