2002 JEEP LIBERTY sensor

CONDITION POSSIBLE CAUSES CORRECTION
15. Thermostat partially or
completely shut.15. Check thermostat operation and
replaces necessary. (Refer to 7 -
COOLING/ENGINE/ENGINE
COOLANT THERMOSTAT -
DIAGNOSIS AND TESTING).
16. Viscous fan drive not operating
properly.16. Check fan drive operation and
replace as necessary. (Refer to 7 -
COOLING/ENGINE/FAN DRIVE
VISCOUS CLUTCH - DIAGNOSIS
AND TESTING).
17. Cylinder head gasket leaking. 17. Check for cylinder head gasket
leaks. (Refer to 7 - COOLING -
DIAGNOSIS AND TESTING). For
repair, (Refer to 9 - ENGINE/
CYLINDER HEAD - REMOVAL).
18. Heater core leaking. 18. Check heater core for leaks.
(Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING/
HEATER CORE - REMOVAL).
Repair as necessary.
19. Electric fan not functioning. 19. Inspect electric fan for proper
operation. Refer to Electric Cooling
Fan in this section. Refer to Group
8W for electric cooling fan and relay
circuit schematic data.
TEMPERATURE GAUGE READING
IS INCONSISTENT (FLUCTUATES,
CYCLES OR IS ERRATIC)1. During cold weather operation,
with the heater blower in the high
position, the gauge reading may
drop slightly.1. A normal condition. No correction
is necessary.
2. Temperature gauge or engine
mounted gauge sensor defective or
shorted. Also, corroded or loose
wiring in this circuit.2. Check operation of gauge and
repair if necessary. Refer to Group
8J, Instrument cluster.
3. Gauge reading rises when
vehicle is brought to a stop after
heavy use (engine still running)3. A normal condition. No correction
is necessary. Gauge should return
to normal range after vehicle is
driven.
4. Gauge reading high after
re-starting a warmed up (hot)
engine.4. A normal condition. No correction
is necessary. The gauge should
return to normal range after a few
minutes of engine operation.
5. Coolant level low in cooling
system (air will build up in the
cooling system causing the
thermostat to open late).5. Check and correct coolant leaks.
(Refer to 7 - COOLING -
DIAGNOSIS AND TESTING).
7 - 8 COOLINGKJ
COOLING (Continued)

CONDITION POSSIBLE CAUSES CORRECTION
STEAM IS COMING FROM THE
FRONT OF VEHICLE NEAR THE
GRILL AREA WHEN WEATHER IS
WET, ENGINE IS WARMED UP
AND RUNNING, AND VEHICLE IS
STATIONARY. TEMPERATURE
GAUGE IS IN NORMAL RANGE1. During wet weather, moisture
(snow, ice or rain condensation) on
the radiator will evaporate when the
thermostat opens. This opening
allows heated water into the
radiator. When the moisture
contacts the hot radiator or
condensor, steam may be emitted.
This usually occurs in cold weather
with no fan or airflow to blow it
away.1. Occasional steam emitting from
this area is normal. No repair is
necessary.
COOLANT COLOR 1. Coolant color is not necessarily
an indication of adequate corrosion
or temperature protection. Do not
rely on coolant color for determining
condition of coolant.1. (Refer to 7 - COOLING/ENGINE/
COOLANT - DESCRIPTION) for
coolant concentration information.
Adjust coolant mixture as
necessary.
COOLANT LEVEL CHANGES IN
COOLANT RESERVE/OVERFLOW
TANK. TEMPERATURE GAUGE IS
IN NORMAL RANGE1. Level changes are to be
expected as coolant volume
fluctuates with engine temperature.
If the level in the tank was between
the FULL and ADD marks at normal
operating temperature, the level
should return to within that range
after operation at elevated
temperatures.1. A normal condition. No repair is
necessary.
FAN RUNS ALL THE TIME 1. Fan control sensors inoperative. 1. Check for DTC's. Verify sensor
readings.
2. Fan control solenoid stuck9on9. 2. Check fan operation speeds.
Refer to fan speed operation table.
3. Fan control solenoid harness
damaged.3. Check for DTC 1499. Repair as
required.
4. Transmission temperature too
high.4. Check for transmission over
temp. DTC.
5. Engine coolant temperature too
high.5. (a) Check coolant level. Correct
level as required.
(b) Thermostat stuck. Replace
thermostat.
(c) Water pump failed. Replace
water pump.
(d) Coolant flow restricted. Clean
radiator.
(e) Air flow over radiator
obstructed.Remove obstruction.
KJCOOLING 7 - 11
COOLING (Continued)

ENGINE
TABLE OF CONTENTS
page page
COOLANT RECOVERY PRESS CONTAINER
DESCRIPTION.........................19
OPERATION...........................19
ENGINE COOLANT TEMPERATURE SENSOR
DESCRIPTION.........................19
OPERATION...........................20
REMOVAL.............................20
INSTALLATION.........................21
ENGINE COOLANT THERMOSTAT
DESCRIPTION - 3.7L ENGINE.............21
OPERATION...........................21
DIAGNOSIS AND TESTING - THERMOSTAT . . . 21
REMOVAL - 3.7L ENGINE.................21
INSTALLATION - 3.7L ENGINE.............22
RADIATOR
DESCRIPTION.........................22
REMOVAL.............................23
CLEANING............................24
INSPECTION..........................24
INSTALLATION.........................24
RADIATOR PRESSURE CAP
DESCRIPTION.........................25
OPERATION...........................25
DIAGNOSIS AND TESTING - RADIATOR
PRESSURE CAP......................25CLEANING............................25
INSPECTION..........................25
RADIATOR FAN - ELECTRIC
DESCRIPTION.........................26
OPERATION...........................26
REMOVAL.............................26
INSTALLATION.........................27
RADIATOR - FAN - VISCOUS
DESCRIPTION.........................27
OPERATION...........................27
DIAGNOSIS AND TESTING - VISCOUS FAN
DRIVE..............................28
REMOVAL.............................28
CLEANING............................29
INSPECTION..........................29
INSTALLATION.........................29
WATER PUMP
DESCRIPTION
DESCRIPTION - WATER PUMP...........29
DESCRIPTION........................29
OPERATION - WATER PUMP..............30
REMOVAL.............................30
CLEANING............................31
INSPECTION..........................31
INSTALLATION.........................31
COOLANT RECOVERY PRESS
CONTAINER
DESCRIPTION
This system works along with the radiator pres-
sure cap. This is done by using thermal expansion
and contraction of the coolant to keep the coolant
free of trapped air. It provides:
²A volume for coolant expansion and contraction.
²A convenient and safe method for checking/ad-
justing coolant level at atmospheric pressure. This is
done without removing the radiator pressure cap.
²Some reserve coolant to the radiator to cover
minor leaks and evaporation or boiling losses.
As the engine cools, a vacuum is formed in the
cooling system of both the radiator and engine. Cool-
ant will then be drawn from the coolant tank and
returned to a proper level in the radiator.
The coolant reservoir/overflow system has a radia-
tor mounted pressurized cap, an overflow tube, and a
plastic coolant reservoir/overflow tank, mounted to
the right side of the cowl. It is mounted to the cowlwith two nuts on top, and a slide bracket on the bot-
tom.
OPERATION
The pressure chamber keeps the coolant free of
trapped air, provides a volume for expansion and con-
traction, and provides a convenient and safe method
for checking and adjusting coolant level at atmo-
spheric pressure. It also provides some reserve cool-
ant to cover minor leaks, evaporation or boiling
losses. The overflow chamber allows coolant recovery
in case of an overheat.
ENGINE COOLANT
TEMPERATURE SENSOR
DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is
used to sense engine coolant temperature. The sensor
protrudes into an engine water jacket.
KJENGINE 7 - 19

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
2.4L
The Engine Coolant Temperature (ECT) sensor is
installed into a water jacket at left front of cylinder
head (Fig. 1).
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. COOLING SYSTEM
MUST BE PARTIALLY DRAINED BEFORE REMOV-
ING THE COOLANT TEMPERATURE SENSOR.
(1) Partially drain cooling system.
(2) Disconnect electrical connector from sensor.
(3) Remove sensor from cylinder head.
3.7L
The Engine Coolant Temperature (ECT) sensor is
installed into a water jacket at front of intake mani-
fold near rear of generator (Fig. 2).
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. COOLING SYSTEM
MUST BE PARTIALLY DRAINED BEFORE REMOV-
ING THE COOLANT TEMPERATURE SENSOR.(1) Partially drain cooling system.
(2) Disconnect electrical connector from sensor.
(3) Remove sensor from intake manifold.
Fig. 1 ECT AND UPPER TIMING BELT COVER/
BOLTS-2.4L
1 - UPPER TIMING BELT COVER
2 - ELECTRICAL CONNECTOR (ECT)
3 - MOUNTING BOLTS (3)
Fig. 2 MAP SENSOR / ECT SENSOR - 3.7L
1 - MOUNTING SCREWS
2 - MAP SENSOR
3 - ECT SENSOR
7 - 20 ENGINEKJ
ENGINE COOLANT TEMPERATURE SENSOR (Continued)

INSTALLATION
(1) Apply thread sealant to sensor threads.
(2) Install sensor to engine.
(3) Tighten sensor to 11 N´m (8 ft. lbs.) torque.
(4) Replace any lost engine coolant.
ENGINE COOLANT
THERMOSTAT
DESCRIPTION - 3.7L 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 3.7L 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. 3).
The same thermostat is used for winter and sum-
mer seasons. An engine should not be operated with-
out a thermostat, except for servicing or testing.
Operating without a thermostat causes other prob-
lems. These are: longer engine warmup time, unreli-
able warmup performance, increased exhaust
emissions and crankcase condensation. This conden-
sation can result in sludge formation.
OPERATION
The wax pellet is located in a sealed container at
the spring end of the thermostat. When heated, the
pellet expands, overcoming closing spring tension
and water pump pressure to force the valve to open.
DIAGNOSIS AND TESTING - THERMOSTAT
ON-BOARD DIAGNOSTICS
All models are equipped with On-Board Diagnos-
tics for certain cooling system components.If the pow-
ertrain control module (PCM) detects low engine
coolant temperature, it will record a Diagnostic Trou-
ble Code (DTC). For other DTC numbers, (Refer to 25
- EMISSIONS CONTROL - DESCRIPTION).
The DTC can also be accessed through the DRB
scan tool.
REMOVAL - 3.7L ENGINE
WARNING: DO NOT LOOSEN RADIATOR DRAIN-
COCK WITH SYSTEM HOT AND PRESSURIZED.
SERIOUS BURNS FROM COOLANT CAN OCCUR.
Do not waste reusable coolant. If solution is clean,
drain coolant into a clean container for reuse.
If thermostat is being replaced, be sure that
replacement is specified thermostat for vehicle model
and engine type.
(1) Disconnect negative battery cable at battery.
(2) Drain cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE).
(3) Raise vehicle on hoist.
(4) Remove splash shield.
(5) Remove lower radiator hose clamp and lower
radiator hose at thermostat housing.
(6) Remove thermostat housing mounting bolts,
thermostat housing and thermostat (Fig. 4).
Fig. 3 Thermostat
1 - FROM HEATER
2 - FROM RADIATOR
3 - TO WATER PUMP
4 - ENGINE BYPASS
5 - THERMOSTAT
KJENGINE 7 - 21
ENGINE COOLANT TEMPERATURE SENSOR (Continued)

RADIATOR FAN - ELECTRIC
DESCRIPTION
The fan (Fig. 12) is electrically controlled by the
powertrain control module (PCM) through the fan
control relay. This relay is located on the left wheel
house in the engine compartment.
OPERATION
The electric radiator cooling fan is controlled by
the Powertrain Control Module (PCM) through the
radiator cooling fan relay. The PCM regulates fan
operation based on input from the engine coolant
temperature sensor, battery temperature sensor,air
conditioning select switch and vehicle speed.
The fan is not energized during engine cranking
regardless of the electrical input from the tempera-
ture sensors and ,air conditioning switch. However, if
engine operation conditions warrant fan engagement,
the fan will run once engine starts.
On vehicles NOT equipped with AC:The relay
is energized when the coolant temperature is above
80É C (176É F), or battery temperature sensor above ±
12É C (10É F). It will then de-energize when coolant
temperature drops below 82É C (180É F), or batter
temperature sensor below ± 9É C ( 16É F).
Vehicles Equipped with AC:In addition to using
coolant temperature and battery temperature sensorto control cooling fan operation, the cooling fan will
also be engaged when the ,air conditioning system is
activated. The relay is also energized when, air con-
ditioning is selected and coolant temperature is
above 95É C ( 203É F), or , air conditioning is selected
and battery temperature sensor is above 41É C (106É
F). It will then de-energize when , air conditioning is
selected and coolant temperature is below 92É C
(198É F), or , air conditioning is selected and battery
temperature is below 38É C (100É F).
REMOVAL
If the fan blade is bent, warped, cracked or dam-
aged in any way, it must be replacedonlywith a
replacement fan blade.Do not attempt to repair a
damaged fan blade.
NOTE: For 3.7L Heavy Duty/Max Cool/Trailer Tow
cooling package, the vicous fan cannot be removed
seperate from the shroud. Both fan and shroud
must be removed together.
(1) Disconnect battery negative cable.
(2) Using special tool 6958 spanner wrench and
8346 adapters, remove the vicous fan from the water
pump (Fig. 13).
(3) Gently lay fan into shroud.
(4) Disconnect the electrical connector for the elec-
tric fan, then disconnect connector from shroud.
Fig. 12 Radiator Cooling Fan - Typical
1 - RADIATOR
2 - ELECTRIC COOLING FAN CONNECTOR
3 - FAN SHROUD
4 - ELECTRIC COOLING FAN
Fig. 13 Viscous Fan and Fan Drive 3.7L
1 - SPECIAL TOOL 6958 SPANNER WRENCH WITH ADAPTER
PINS 8346
2-FAN
7 - 26 ENGINEKJ

DIAGNOSIS AND TESTING - COOLING SYSTEM
DIAGNOSIS CHART
COOLING SYSTEM DIAGNOSIS CHART
CONDITION POSSIBLE CAUSES CORRECTION
TEMPERATURE GAUGE READS
LOW1. Has a Diagnostic Trouble Code
(DTC) been set indicating a stuck
open thermostat?1. Refer to (Refer to 25 -
EMISSIONS CONTROL -
DESCRIPTION) for On-Board
Diagnostics and DTC information.
Replace thermostat if necessary.
2. Is the temperature sending unit
connected?2. Check the temperature sensor
connector. (Refer to 7 - COOLING/
ENGINE/ENGINE COOLANT TEMP
SENSOR - DESCRIPTION). Repair
connector if necessary.
3. Is the temperature gauge
operating OK?3. Check gauge operation. Repair
as necessary.
4. Coolant level low in cold ambient
temperatures accompanied with
poor heater performance.4. Check coolant level in the coolant
pressure botttle and the radiator.
Inspect system for leaks. Repair
leaks as necessary.
5. Improper operation of internal
heater doors or heater controls.5. Inspect heater and repair as
necessary. (Refer to 24 - HEATING
& AIR CONDITIONING -
DIAGNOSIS AND TESTING)
6. Electric fan functioning when not
required.6. Inspect electric fan for proper
operation. Refer to Electric Cooling
Fan in this section. Refer to group
8W for electric cooling fan and relay
circuit schematic data.
KJCOOLING - 2.4L7s-5
COOLING - 2.4L (Continued)

CONDITION POSSIBLE CAUSES CORRECTION
TEMPERATURE GAUGE READING
IS INCONSISTENT (FLUCTUATES,
CYCLES OR IS ERRATIC)1. During cold weather operation,
with the heater blower in the high
position, the gauge reading may
drop slightly.1. A normal condition. No correction
is necessary.
2. Temperature gauge or engine
mounted gauge sensor defective or
shorted. Also, corroded or loose
wiring in this circuit.2. Check operation of gauge and
repair if necessary. Refer to Group
8J, Instrument cluster.
3. Gauge reading rises when
vehicle is brought to a stop after
heavy use (engine still running)3. A normal condition. No correction
is necessary. Gauge should return
to normal range after vehicle is
driven.
4. Gauge reading high after
re-starting a warmed up (hot)
engine.4. A normal condition. No correction
is necessary. The gauge should
return to normal range after a few
minutes of engine operation.
5. Coolant level low in cooling
system (air will build up in the
cooling system causing the
thermostat to open late).5. Check and correct coolant leaks.
(Refer to 7 - COOLING -
DIAGNOSIS AND TESTING).
6. Cylinder head gasket leaking
allowing exhaust gas to enter
cooling system causing a
thermostat to open late.6. (a) Check for cylinder head
gasket leaks. (Refer to 7 -
COOLING - DIAGNOSIS AND
TESTING).
(b) Check for coolant in the engine
oil. Inspect for white steam emitting
from the exhaust system. Repair as
necessary.
7. Water pump impeller loose on
shaft.7. Check water pump and replace
as necessary. (Refer to 7 -
COOLING/ENGINE/WATER PUMP -
DIAGNOSIS AND TESTING).
8. Loose accessory drive belt.
(water pump slipping)8. (Refer to 7 - COOLING/
ACCESSORY DRIVE/DRIVE BELTS
- DIAGNOSIS AND TESTING).
Check and correct as necessary.
9. Air leak on the suction side of
the water pump allows air to build
up in cooling system causing
thermostat to open late.9. Locate leak and repair as
necessary.
PRESSURE CAP IS BLOWING
OFF STEAM AND/OR COOLANT
TO COOLANT TANK.
TEMPERATURE GAUGE READING
MAY BE ABOVE NORMAL BUT
NOT HIGH. COOLANT LEVEL MAY
BE HIGH IN COOLANT RESERVE/
OVERFLOW TANK1. Pressure relief valve in pressure
bottle cap is defective.1. Check condition of radiator cap
and cap seals. (Refer to 7 -
COOLING/ENGINE/RADIATOR
PRESSURE CAP - DIAGNOSIS
AND TESTING). Replace cap as
necessary.
7s - 8 COOLING - 2.4LKJ
COOLING - 2.4L (Continued)