2002 JEEP GRAND CHEROKEE Temperature sensor

INSTALLATION
INSTALLATION - 4.0L
The Intake Manifold Air Temperature (IAT) sensor
is installed into the intake manifold plenum near the
front of the throttle body (Fig. 27).
(1) Install sensor into intake manifold. Tighten
sensor to 28 N´m (20 ft. lbs.) torque.
(2) Connect electrical connector to sensor.
INSTALLATION - 4.7L
Threaded Type Sensor
(1) Install sensor (Fig. 28) into intake manifold.
Tighten sensor to 28 N´m (20 ft. lbs.) torque.
(2) Connect electrical connector to sensor.
Snap-In Type Sensor
(1) Check condition of sensor o-ring (Fig. 30).
(2) Clean sensor mounting hole in intake manifold.(3) Position sensor (Fig. 29) into intake manifold
and rotate clockwise until past release tab.
(4) Install electrical connector.
Fig. 28 IAT - 4.7L (THREADED TYPE)
1 - THROTTLE BODY
2 - TPS
3 - IAC MOTOR
4 - IAT SENSOR (THREADED TYPE)
5 - MOUNTING SCREWS
Fig. 29 IAT SENSOR - 4.7L (SNAP-IN TYPE)
1 - LEFT SIDE OF THROTTLE BODY
2 - ELEC. CONNECT.
3 - IAT SENSOR
4 - RELEASE TAB
Fig. 30 IAT SENSOR TAB / O-RING - 4.7L (SNAP-IN
TYPE)
1 - IAT SENSOR
2 - SENSOR O-RING
3 - RELEASE TAB
WJFUEL INJECTION 14 - 47
INTAKE AIR TEMPERATURE SENSOR (Continued)

MAP SENSOR
DESCRIPTION
DESCRIPTION
On the 4.0L six-cylinder engine the MAP sensor is
mounted to the engine throttle body. On the 4.7L V-8
engine the MAP sensor is mounted to front of the
intake manifold.
DESCRIPTION - 4.7L
The MAP sensor is located on the front of the
intake manifold. An o-ring seals the sensor to the
intake manifold.
OPERATION
The MAP sensor is used as an input to the Power-
train Control Module (PCM). It contains a silicon
based sensing unit to provide data on the manifold
vacuum that draws the air/fuel mixture into the com-
bustion chamber. The PCM requires this information
to determine injector pulse width and spark advance.
When manifold absolute pressure (MAP) equals
Barometric pressure, the pulse width will be at max-
imum.
A 5 volt reference is supplied from the PCM and
returns a voltage signal to the PCM that reflects
manifold pressure. The zero pressure reading is 0.5V
and full scale is 4.5V. For a pressure swing of 0±15
psi, the voltage changes 4.0V. To operate the sensor,
it is supplied a regulated 4.8 to 5.1 volts. Ground is
provided through the low-noise, sensor return circuit
at the PCM.
The MAP sensor input is the number one contrib-
utor to fuel injector pulse width. The most important
function of the MAP sensor is to determine baromet-
ric pressure. The PCM needs to know if the vehicle is
at sea level or at a higher altitude, because the air
density changes with altitude. It will also help to cor-
rect for varying barometric pressure. Barometric
pressure and altitude have a direct inverse correla-
tion; as altitude goes up, barometric goes down. At
key-on, the PCM powers up and looks at MAP volt-
age, and based upon the voltage it sees, it knows the
current barometric pressure (relative to altitude).
Once the engine starts, the PCM looks at the voltage
again, continuously every 12 milliseconds, and com-
pares the current voltage to what it was at key-on.
The difference between current voltage and what it
was at key-on, is manifold vacuum.
During key-on (engine not running) the sensor
reads (updates) barometric pressure. A normal range
can be obtained by monitoring a known good sensor.
As the altitude increases, the air becomes thinner
(less oxygen). If a vehicle is started and driven to avery different altitude than where it was at key-on,
the barometric pressure needs to be updated. Any
time the PCM sees Wide Open Throttle (WOT), based
upon Throttle Position Sensor (TPS) angle and RPM,
it will update barometric pressure in the MAP mem-
ory cell. With periodic updates, the PCM can make
its calculations more effectively.
The PCM uses the MAP sensor input to aid in cal-
culating the following:
²Manifold pressure
²Barometric pressure
²Engine load
²Injector pulse-width
²Spark-advance programs
²Shift-point strategies (certain automatic trans-
missions only)
²Idle speed
²Decel fuel shutoff
The MAP sensor signal is provided from a single
piezoresistive element located in the center of a dia-
phragm. The element and diaphragm are both made
of silicone. As manifold pressure changes, the dia-
phragm moves causing the element to deflect, which
stresses the silicone. When silicone is exposed to
stress, its resistance changes. As manifold vacuum
increases, the MAP sensor input voltage decreases
proportionally. The sensor also contains electronics
that condition the signal and provide temperature
compensation.
The PCM recognizes a decrease in manifold pres-
sure by monitoring a decrease in voltage from the
reading stored in the barometric pressure memory
cell. The MAP sensor is a linear sensor; meaning as
pressure changes, voltage changes proportionately.
The range of voltage output from the sensor is usu-
ally between 4.6 volts at sea level to as low as 0.3
volts at 26 in. of Hg. Barometric pressure is the pres-
sure exerted by the atmosphere upon an object. At
sea level on a standard day, no storm, barometric
pressure is approximately 29.92 in Hg. For every 100
feet of altitude, barometric pressure drops .10 in. Hg.
If a storm goes through it can change barometric
pressure from what should be present for that alti-
tude. You should know what the average pressure
and corresponding barometric pressure is for your
area.
REMOVAL
REMOVAL - 4.0L
The MAP sensor is mounted to the side of the
throttle body (Fig. 40). An L-shaped rubber fitting is
used to connect the MAP sensor to throttle body (Fig.
31).
(1) Remove air cleaner duct and air resonator box
at throttle body.
14 - 48 FUEL INJECTIONWJ

The other two heater elements (downstream sen-
sors 1/2 and 2/2) are controlled by the downstream
heater relay through output signals from the PCM.
To avoid a large simultaneous current surge, power
is delayed to the 2 downstream heater elements by
the PCM for approximately 2 seconds.
REMOVAL
(1) Remove PDC cover.
(2) Remove relay from PDC.
(3) Check condition of relay terminals and PDC
connector terminals for damage or corrosion. Repair
if necessary before installing relay.
(4) Check for pin height (pin height should be the
same for all terminals within the PDC connector).
Repair if necessary before installing relay.
INSTALLATION
(1) Install relay to PDC.
(2) Install cover to PDC.
O2S SENSOR
DESCRIPTION
The Oxygen Sensors (O2S) are attached to, and
protrude into the vehicle exhaust system. Depending
on the emission package, the vehicle may use a total
of either 2 or 4 sensors.
Federal Emissions Package:Two sensors are
used: upstream (referred to as 1/1) and downstream
(referred to as 1/2). With this emission package, the
upstream sensor (1/1) is located just before the main
catalytic convertor. The downstream sensor (1/2) is
located just after the main catalytic convertor.
4.7L V-8 With California Emissions Package:
On this emissions package, 4 sensors are used: 2
upstream (referred to as 1/1 and 2/1) and 2 down-
stream (referred to as 1/2 and 2/2). With this emis-
sion package, the right upstream sensor (2/1) is
located in the right exhaust downpipe just before the
mini-catalytic convertor. The left upstream sensor
(1/1) is located in the left exhaust downpipe just
before the mini-catalytic convertor. The right down-
stream sensor (2/2) is located in the right exhaust
downpipe just after the mini-catalytic convertor, and
before the main catalytic convertor. The left down-
stream sensor (1/2) is located in the left exhaust
downpipe just after the mini-catalytic convertor, and
before the main catalytic convertor.
4.0L 6±Cylinder With California Emissions
Package:On this emissions package, 4 sensors are
used: 2 upstream (referred to as 1/1 and 2/1) and 2
downstream (referred to as 1/2 and 2/2). With this
emission package, the rear/upper upstream sensor
(2/1) is located in the exhaust downpipe just beforethe rear mini-catalytic convertor. The front/upper
upstream sensor (1/1) is located in the exhaust down-
pipe just before the front mini-catalytic convertor.
The rear/lower downstream sensor (2/2) is located in
the exhaust downpipe just after the rear mini-cata-
lytic convertor, and before the main catalytic conver-
tor. The front/lower downstream sensor (1/2) is
located in the exhaust downpipe just after the front
mini-catalytic convertor, and before the main cata-
lytic convertor.
OPERATION
An O2 sensor is a galvanic battery that provides
the PCM with a voltage signal (0-1 volt) inversely
proportional to the amount of oxygen in the exhaust.
In other words, if the oxygen content is low, the volt-
age output is high; if the oxygen content is high the
output voltage is low. The PCM uses this information
to adjust injector pulse-width to achieve the
14.7±to±1 air/fuel ratio necessary for proper engine
operation and to control emissions.
The O2 sensor must have a source of oxygen from
outside of the exhaust stream for comparison. Cur-
rent O2 sensors receive their fresh oxygen (outside
air) supply through the O2 sensor case housing.
Four wires (circuits) are used on each O2 sensor: a
12±volt feed circuit for the sensor heating element; a
ground circuit for the heater element; a low-noise
sensor return circuit to the PCM, and an input cir-
cuit from the sensor back to the PCM to detect sen-
sor operation.
Oxygen Sensor Heaters/Heater Relays:
Depending on the emissions package, the heating ele-
ments within the sensors will be supplied voltage
from either the ASD relay, or 2 separate oxygen sen-
sor relays. Refer to Wiring Diagrams to determine
which relays are used.
The O2 sensor uses a Positive Thermal Co-efficient
(PTC) heater element. As temperature increases,
resistance increases. At ambient temperatures
around 70ÉF, the resistance of the heating element is
approximately 4.5 ohms on 4.0L engines. It is
approximately 13.5 ohms on the 4.7L engine. As the
sensor's temperature increases, resistance in the
heater element increases. This allows the heater to
maintain the optimum operating temperature of
approximately 930É-1100ÉF (500É-600É C). Although
the sensors operate the same, there are physical dif-
ferences, due to the environment that they operate
in, that keep them from being interchangeable.
Maintaining correct sensor temperature at all
times allows the system to enter into closed loop
operation sooner. Also, it allows the system to remain
in closed loop operation during periods of extended
idle.
14 - 50 FUEL INJECTIONWJ
O2S HEATER RELAY (Continued)

STANDARD PROCEDURE - TORQUE
CONVERTER DRAINBACK VALVE........134
TRANSMISSION TEMPERATURE SENSOR
DESCRIPTION........................134
OPERATION..........................134
VALVE BODY
DESCRIPTION........................135
OPERATION..........................139REMOVAL............................154
DISASSEMBLY........................155
CLEANING...........................165
INSPECTION.........................166
ASSEMBLY...........................167
INSTALLATION........................175
ADJUSTMENTS - VALVE BODY...........175
AUTOMATIC TRANSMISSION -
42RE
DESCRIPTION
The 42RE is a four speed fully automatic transmis-
sion (Fig. 1) with an electronic governor. The 42RE is
equipped with a lock-up clutch in the torque con-
verter. First through third gear ranges are provided
by the clutches, bands, overrunning clutch, and plan-
etary gear sets in the transmission. Fourth gear
range is provided by the overdrive unit that contains
an overdrive clutch, direct clutch, planetary gear set,
and overrunning clutch.The transmission contains a front, rear, and direct
clutch which function as the input driving compo-
nents. It also contains the kickdown (front) and the
low/reverse (rear) bands which, along with the over-
running clutch and overdrive clutch, serve as the
holding components. The driving and holding compo-
nents combine to select the necessary planetary gear
components, in the front, rear, or overdrive planetary
gear set, transfer the engine power from the input
shaft through to the output shaft.
The valve body is mounted to the lower side of the
transmission and contains the valves to control pres-
sure regulation, fluid flow control, and clutch/band
application. The oil pump is mounted at the front of
the transmission and is driven by the torque con-
verter hub. The pump supplies the oil pressure nec-
essary for clutch/band actuation and transmission
lubrication.
WJAUTOMATIC TRANSMISSION - 42RE 21 - 3

(8) Engine starts must be possible with shifter
lever in PARK or NEUTRAL gate positions only.
Engine starts must not be possible in any other gate
positions other than PARK or NEUTRAL.
(9) With shifter lever handle push-button not
depressed and lever detent in:
²PARK position- apply forward force on center of
handle and remove pressure. Engine start must be
possible.
²PARK position- apply rearward force on center
of handle and remove pressure. Engine start must be
possible.
²NEUTRAL position- engine start must be possi-
ble.
²NEUTRAL position, engine running and brakes
applied- Apply forward force on center of shift han-
dle. Transmission should not be able to shift into
REVERSE detent.
ELECTRONIC GOVERNOR
DESCRIPTION
Governor pressure is controlled electronically. Com-
ponents used for governor pressure control include:
²Governor body
²Valve body transfer plate
²Governor pressure solenoid valve
²Governor pressure sensor
²Fluid temperature thermistor
²Throttle position sensor (TPS)
²Transmission speed sensor
²Powertrain control module (PCM)
GOVERNOR PRESSURE SOLENOID VALVE
The solenoid valve is a duty-cycle solenoid which
regulates the governor pressure needed for upshifts
and downshifts. It is an electro-hydraulic device
located in the governor body on the valve body trans-
fer plate (Fig. 73).
GOVERNOR PRESSURE SENSOR
The governor pressure sensor measures output
pressure of the governor pressure solenoid valve (Fig.
74).
GOVERNOR BODY AND TRANSFER PLATE
The transfer plate is designed to supply transmis-
sion line pressure to the governor pressure solenoid
valve and to return governor pressure.
The governor pressure solenoid valve is mounted in
the governor body. The body is bolted to the lower
side of the transfer plate (Fig. 74).
GOVERNOR PRESSURE CURVES
There are four governor pressure curves pro-
grammed into the transmission control module. The
different curves allow the control module to adjust
governor pressure for varying conditions. One curve
is used for operation when fluid temperature is at, or
below, ±1ÉC (30ÉF). A second curve is used when fluid
temperature is at, or above, 10ÉC (50ÉF) during nor-
mal city or highway driving. A third curve is used
during wide-open throttle operation. The fourth curve
is used when driving with the transfer case in low
range.
OPERATION
Compensation is required for performance varia-
tions of two of the input devices. Though the slope of
the transfer functions is tightly controlled, offset may
vary due to various environmental factors or manu-
facturing tolerances.
The pressure transducer is affected by barometric
pressure as well as temperature. Calibration of the
zero pressure offset is required to compensate for
shifting output due to these factors.
Fig. 73 Governor Pressure Solenoid Valve
1 - SOLENOID FILTER
2 - GOVERNOR PRESSURE SOLENOID
Fig. 74 Governor Pressure Sensor
1 - GOVERNOR BODY
2 - GOVERNOR PRESSURE SENSOR/TRANSMISSION FLUID
TEMPERATURE THERMISTOR
WJAUTOMATIC TRANSMISSION - 42RE 21 - 65
BRAKE TRANSMISSION SHIFT INTERLOCK MECHANISM (Continued)

Normal calibration will be performed when sump
temperature is above 50 degrees F, or in the absence
of sump temperature data, after the first 10 minutes
of vehicle operation. Calibration of the pressure
transducer offset occurs each time the output shaft
speed falls below 200 RPM. Calibration shall be
repeated each 3 seconds the output shaft speed is
below 200 RPM. A 0.5 second pulse of 95% duty cycle
is applied to the governor pressure solenoid valve
and the transducer output is read during this pulse.
Averaging of the transducer signal is necessary to
reject electrical noise.
Under cold conditions (below 50 degrees F sump),
the governor pressure solenoid valve response may
be too slow to guarantee 0 psi during the 0.5 second
calibration pulse. Calibration pulses are continued
during this period, however the transducer output
valves are discarded. Transducer offset must be read
at key-on, under conditions which promote a stable
reading. This value is retained and becomes the off-
set during the9cold9period of operation.
GOVERNOR PRESSURE SOLENOID VALVE
The inlet side of the solenoid valve is exposed to
normal transmission line pressure. The outlet side of
the valve leads to the valve body governor circuit.
The solenoid valve regulates line pressure to pro-
duce governor pressure. The average current sup-
plied to the solenoid controls governor pressure. One
amp current produces zero kPa/psi governor pres-
sure. Zero amps sets the maximum governor pres-
sure.
The powertrain control module (PCM) turns on the
trans control relay which supplies electrical power to
the solenoid valve. Operating voltage is 12 volts
(DC). The PCM controls the ground side of the sole-
noid using the governor pressure solenoid control cir-
cuit.
GOVERNOR PRESSURE SENSOR
The sensor output signal provides the necessary
feedback to the PCM. This feedback is needed to ade-
quately control governor pressure.
GOVERNOR BODY AND TRANSFER PLATE
The transfer plate channels line pressure to the
solenoid valve through the governor body. It also
channels governor pressure from the solenoid valve
to the governor circuit. It is the solenoid valve that
develops the necessary governor pressure.
GOVERNOR PRESSURE CURVES
LOW TRANSMISSION FLUID TEMPERATURE
When the transmission fluid is cold the conven-
tional governor can delay shifts, resulting in higherthan normal shift speeds and harsh shifts. The elec-
tronically controlled low temperature governor pres-
sure curve is higher than normal to make the
transmission shift at normal speeds and sooner. The
PCM uses a temperature sensor in the transmission
oil sump to determine when low temperature gover-
nor pressure is needed.
NORMAL OPERATION
Normal operation is refined through the increased
computing power of the PCM and through access to
data on engine operating conditions provided by the
PCM that were not available with the previous
stand-alone electronic module. This facilitated the
development of a load adaptive shift strategy - the
ability to alter the shift schedule in response to vehi-
cle load condition. One manifestation of this capabil-
ity is grade9hunting9prevention - the ability of the
transmission logic to delay an upshift on a grade if
the engine does not have sufficient power to main-
tain speed in the higher gear. The 3-2 downshift and
the potential for hunting between gears occurs with a
heavily loaded vehicle or on steep grades. When
hunting occurs, it is very objectionable because shifts
are frequent and accompanied by large changes in
noise and acceleration.
WIDE OPEN THROTTLE OPERATION
In wide-open throttle (WOT) mode, adaptive mem-
ory in the PCM assures that up-shifts occur at the
preprogrammed optimum speed. WOT operation is
determined from the throttle position sensor, which
is also a part of the emission control system. The ini-
tial setting for the WOT upshift is below the opti-
mum engine speed. As WOT shifts are repeated, the
PCM learns the time required to complete the shifts
by comparing the engine speed when the shifts occur
to the optimum speed. After each shift, the PCM
adjusts the shift point until the optimum speed is
reached. The PCM also considers vehicle loading,
grade and engine performance changes due to high
altitude in determining when to make WOT shifts. It
does this by measuring vehicle and engine accelera-
tion and then factoring in the shift time.
TRANSFER CASE LOW RANGE OPERATION
On four-wheel drive vehicles operating in low
range, the engine can accelerate to its peak more
rapidly than in Normal range, resulting in delayed
shifts and undesirable engine9flare.9The low range
governor pressure curve is also higher than normal
to initiate upshifts sooner. The PCM compares elec-
tronic vehicle speed signal used by the speedometer
to the transmission output shaft speed signal to
determine when the transfer case is in low range.
21 - 66 AUTOMATIC TRANSMISSION - 42REWJ
ELECTRONIC GOVERNOR (Continued)

PROCEDURE TWO
(1) Start engine and apply parking brake.
(2) Shift the transmission into DRIVE for approxi-
mately 2 seconds.
(3) Shift the transmission into REVERSE for
approximately 2 seconds.
(4) Shift the transmission into PARK.
(5) Hook up DRBtscan tool and select engine.
(6) Select sensors.
(7) Read the transmission temperature value.
(8) Compare the fluid temperature value with the
figure. (Fig. 88)
(9) Adjust transmission fluid level shown on the
dipstick according to the figure.NOTE: After adding any fluid to the transmission,
wait a minimum of 2 minutes for the oil to fully
drain from the fill tube into the transmission before
rechecking the fluid level.
(10) Check transmission for leaks.
STANDARD PROCEDURE - FLUID AND FILTER
REPLACEMENT
For proper service intervals (Refer to LUBRICA-
TION & MAINTENANCE/MAINTENANCE SCHED-
ULES - DESCRIPTION). The service fluid fill after a
filter change is approximately 3.8 liters (4.0 quarts).
REMOVAL
(1) Hoist and support vehicle on safety stands.
(2) Place a large diameter shallow drain pan
beneath the transmission pan.
(3) Remove bolts holding front and sides of pan to
transmission (Fig. 89).
(4) Loosen bolts holding rear of pan to transmis-
sion.
(5) Slowly separate front of pan and gasket away
from transmission allowing the fluid to drain into
drain pan.
(6) Hold up pan and remove remaining bolt hold-
ing pan to transmission.
Fig. 88 42/44RE Fluid Fill Graph
Fig. 87 Dipstick Fluid Level Marks - Typical
1 - DIPSTICK
2 - MAXIMUM CORRECT FLUID LEVEL
3 - ACCEPTABLE FLUID LEVEL
WJAUTOMATIC TRANSMISSION - 42RE 21 - 71
FLUID AND FILTER (Continued)

TORQUE CONVERTER
DRAINBACK VALVE
DESCRIPTION
The drainback valve is located in the transmission
cooler outlet (pressure) line.
OPERATION
The valve prevents fluid from draining from the
converter into the cooler and lines when the vehicle
is shut down for lengthy periods. Production valves
have a hose nipple at one end, while the opposite end
is threaded for a flare fitting. All valves have an
arrow (or similar mark) to indicate direction of flow
through the valve.
STANDARD PROCEDURE - TORQUE
CONVERTER DRAINBACK VALVE
The converter drainback check valve is located in
the cooler outlet (pressure) line near the radiator
tank. The valve prevents fluid drainback when the
vehicle is parked for lengthy periods. The valve check
ball is spring loaded and has an opening pressure of
approximately 2 psi.
The valve is serviced as an assembly; it is not
repairable. Do not clean the valve if restricted, or
contaminated by sludge, or debris. If the valve fails,
or if a transmission malfunction occurs that gener-
ates significant amounts of sludge and/or clutch par-
ticles and metal shavings, the valve must be
replaced.
The valve must be removed whenever the cooler
and lines are reverse flushed. The valve can be flow
tested when necessary. The procedure is exactly the
same as for flow testing a cooler.
If the valve is restricted, installed backwards, or in
the wrong line, it will cause an overheating condition
and possible transmission failure.
CAUTION: The drainback valve is a one-way flow
device. It must be properly oriented in terms of flow
direction for the cooler to function properly. The
valve must be installed in the pressure line. Other-
wise flow will be blocked and would cause an over-
heating condition and eventual transmission failure.
TRANSMISSION
TEMPERATURE SENSOR
DESCRIPTION
Transmission fluid temperature readings are sup-
plied to the transmission control module by the ther-
mistor (Fig. 254). The temperature readings are used
to control engagement of the fourth gear overdrive
clutch, the converter clutch, and governor pressure.
Normal resistance value for the thermistor at room
temperature is approximately 2000 ohms.
The thermistor is part of the governor pressure
sensor assembly and is immersed in transmission
fluid at all times.
OPERATION
The PCM prevents engagement of the converter
clutch and overdrive clutch, when fluid temperature
is below approximately 10ÉC (50ÉF).
If fluid temperature exceeds 126ÉC (260ÉF), the
PCM causes a 4-3 downshift and engage the con-
verter clutch. Engagement is according to the third
gear converter clutch engagement schedule.
The overdrive OFF lamp in the instrument panel
illuminates when the shift back to third occurs. The
transmission will not allow fourth gear operation
until fluid temperature decreases to approximately
110ÉC (230ÉF).
Fig. 254 Governor Pressure Sensor
1 - GOVERNOR BODY
2 - GOVERNOR PRESSURE SENSOR/TRANSMISSION FLUID
TEMPERATURE THERMISTOR
21 - 134 AUTOMATIC TRANSMISSION - 42REWJ