Electronic control module JEEP GRAND CHEROKEE 2003 WJ / 2.G Workshop Manual

POSITION SENSOR
DESCRIPTION
The transfer case position sensor (Fig. 95) is an
electronic device whose output can be interpreted to
indicate the transfer case's current operating mode.
The sensor consists of a five position, resistive multi-
plexed circuit which returns a specific resistance
value to the Powertrain Control Module (PCM) for
each transfer case operating mode. The sensor is
located on the top of the transfer case, just left of the
transfer case centerline and rides against the sector
plate roostercomb. The PCM supplies 5VDC (+/-
0.5V) to the sensor and monitors the return voltage
to determine the sector plate, and therefore the
transfer case, position.
OPERATION
During normal vehicle operation, the Powertrain
Control Module (PCM) monitors the transfer case
position sensor return voltage to determine the oper-
ating mode of the transfer case. Refer to the Operat-
ing Mode Versus Resistance table for the correct
resistance for each position (Fig. 96).
OPERATING MODE VERSUS RESISTANCE
SENSOR POSITION OPERATING MODE SENSOR RESISTANCE (ohms)
1 2WD 1124-1243
2 4WD PART TIME 650-719
3 4WD FULL TIME 389-431
4 NEUTRAL 199-221
5 4WD LOW 57-64
Fig. 96 Position Sensor Linear Movement
1 - POSITION 1 - 10mm  0.5mm
2 - POSITION 2 - 12mm  0.5mm
3 - POSITION 3 - 14mm  0.5mm
4 - POSITION 4 - 16mm  0.5mm
5 - POSITION 5 - 18mm  0.5mm
6 - POSITION 6 - 20mm 0.5mm - FULL EXTENSION
Fig. 95 Transfer Case Position Sensor and
Connector
1 - TRANSFER CASE POSITION SENSOR CONNECTOR
2 - TRANSFER CASE POSITION SENSOR
3 - TRANSFER CASE
4 - OUTPUT SPEED SENSOR CONNECTOR
WJTRANSFER CASE - NV242 21 - 311

OPERATION
OPERATION - HEATER AND AIR CONDITIONER
Outside fresh air enters the vehicle through the
cowl top opening at the base of the windshield, and
passes through a plenum chamber to the HVAC sys-
tem blower housing. Air flow velocity can then be
adjusted with the blower motor speed selector switch
on the a/c heater control panel. The air intake open-
ings must be kept free of snow, ice, leaves, and other
obstructions for the HVAC system to receive a suffi-
cient volume of outside air.
It is also important to keep the air intake openings
clear of debris because leaf particles and other debris
that is small enough to pass through the cowl ple-
num screen can accumulate within the HVAC hous-
ing. The closed, warm, damp and dark environment
created within the HVAC housing is ideal for the
growth of certain molds, mildews and other fungi.
Any accumulation of decaying plant matter provides
an additional food source for fungal spores, which
enter the housing with the fresh air. Excess debris,
as well as objectionable odors created by decaying
plant matter and growing fungi can be discharged
into the passenger compartment during HVAC sys-
tem operation.
Both the manual and AZC heater and air condi-
tioner are blend-air type systems. In a blend-air sys-
tem, a blend door controls the amount of
unconditioned air (or cooled air from the evaporator)
that is allowed to flow through, or around, the heater
core. A temperature control knob on the a/c heater
control panel determines the discharge air tempera-
ture by energizing the blend door actuator, which
operates the blend door. This allows an almost imme-
diate control of the output air temperature of the sys-
tem. The AZC system will have separate blend doors
and temperature controls for each front seat occu-
pant.
The mode control knob on the a/c heater control
panel is used to direct the conditioned air to the
selected system outlets. On manual temperature con-
trol systems, the mode control knob switches engine
vacuum to control the mode doors, which are oper-
ated by vacuum actuators. On AZC systems, the
mode control knob switches electrical current to con-
trol the mode doors, which are operated by electronic
actuators.
The outside air intake can be shut off on manual
temperature control systems by selecting the Recircu-
lation Mode with the mode control knob. The outside
air intake can be shut off on Automatic Zone Control
(AZC) type system by pushing the Recirculation
Mode button. This will operate the recirculation door
that closes off the outside fresh air intake and recir-
culates the air that is already inside the vehicle.The air conditioner for all models is designed for
the use of non-CFC, R-134a refrigerant. The air con-
ditioning system has an evaporator to cool and dehu-
midify the incoming air prior to blending it with the
heated air. This air conditioning system uses a ther-
mal expansion valve to meter refrigerant flow to the
evaporator coil. To maintain minimum evaporator
temperature and prevent evaporator freezing, the
system utilizes an evaporator thermister probe with
the appropriate operating logic located in the body
control module (BCM).
OPERATION - REFRIGERANT SYSTEM SERVICE
PORT
The high pressure service port is located on the liq-
uid line near the receiver/drier. The low pressure ser-
vice port is located on the suction line near the
evaporator at the rear of the engine compartment.
Each of the service ports has a threaded plastic
protective cap installed over it from the factory. After
servicing the refrigerant system, always reinstall
both of the service port caps.
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - A/C
PERFORMANCE
The air conditioning system is designed to provide
the passenger compartment with low temperature
and low specific humidity air. The evaporator, located
in the HVAC housing on the dash panel below the
instrument panel, is cooled to temperatures near the
freezing point. As warm damp air passes through the
cooled evaporator, the air transfers its heat to the
refrigerant in the evaporator and the moisture in the
air condenses on the evaporator fins. During periods
of high heat and humidity, an air conditioning sys-
tem will be more effective in the Recirculation Mode.
With the system in the Recirculation Mode, only air
from the passenger compartment passes through the
evaporator. As the passenger compartment air dehu-
midifies, the air conditioning system performance
levels improve.
Humidity has an important bearing on the tempera-
ture of the air delivered to the interior of the vehicle. It
is important to understand the effect that humidity has
on the performance of the air conditioning system.
When humidity is high, the evaporator has to perform a
double duty. It must lower the air temperature, and it
must lower the temperature of the moisture in the air
that condenses on the evaporator fins. Condensing the
moisture in the air transfers heat energy into the evap-
orator fins and tubing. This reduces the amount of heat
the evaporator can absorb from the air. High humidity
greatly reduces the ability of the evaporator to lower
the temperature of the air.
24 - 2 HEATING & AIR CONDITIONINGWJ
HEATING & AIR CONDITIONING (Continued)

A/C COMPRESSOR CLUTCH
DESCRIPTION
The compressor clutch assembly consists of a sta-
tionary electromagnetic coil, a hub bearing and pul-
ley assembly, and a clutch plate (Fig. 4). The
electromagnetic coil unit and the hub bearing and
pulley assembly are each retained on the nose of the
compressor front housing with snap rings. The clutch
plate is keyed to the compressor shaft and secured
with a bolt.
OPERATION
The compressor clutch components provide the
means to engage and disengage the compressor from
the engine serpentine accessory drive belt. When the
clutch coil is energized, it magnetically draws the
clutch into contact with the pulley and drives the
compressor shaft. When the coil is not energized, the
pulley freewheels on the clutch hub bearing, which is
part of the pulley. The compressor clutch and coil are
the only serviced parts on the compressor.
The compressor clutch engagement is controlled by
several components: the a/c switch on the a/c heater
control panel, the Automatic Zone Control (AZC) con-
trol module (if the vehicle is so equipped), the evap-
orator probe, the a/c high pressure transducer, the
a/c compressor clutch relay, the body control module
(BCM) and the Powertrain Control Module (PCM).
The PCM may delay compressor clutch engagement
for up to thirty seconds. Refer to Electronic Control
Modules for more information on the PCM controls.
DIAGNOSIS AND TESTING - COMPRESSOR
CLUTCH COIL
For circuit descriptions and diagrams, refer to the
appropriate wiring diagrams. The battery must be
fully-charged before performing the following tests.
Refer to Battery for more information.
(1) Connect an ammeter (0 to 10 ampere scale) in
series with the clutch coil terminal. Use a voltmeter
(0 to 20 volt scale) with clip-type leads for measuring
the voltage across the battery and the compressor
clutch coil.
(2) With the a/c heater mode control switch in any
a/c mode, the a/c heater control a/c switch in the ON
position, and the blower motor switch in the lowest
speed position, start the engine and run it at normal
idle.
(3) The compressor clutch coil voltage should read
within 0.2 volts of the battery voltage. If there is
voltage at the clutch coil, but the reading is not
within 0.2 volts of the battery voltage, test the clutch
coil feed circuit for excessive voltage drop and repair
as required. If there is no voltage reading at the
clutch coil, use a DRBIIItscan tool and the appro-
priate diagnostic information for testing of the com-
pressor clutch circuit. The following components
must be checked and repaired as required before you
can complete testing of the clutch coil:
²Fuses in the junction block and the Power Dis-
tribution Center (PDC)
²A/C heater mode control switch
²A/C compressor clutch relay
²A/C high pressure transducer
²A/C evaporator probe
²Powertrain Control Module (PCM)
²Body Control Module (BCM)
(4) The compressor clutch coil is acceptable if the
current draw measured at the clutch coil is 2.0 to 3.9
amperes with the electrical system voltage at 11.5 to
12.5 volts. This should only be checked with the work
area temperature at 21É C (70É F). If system voltage
is more than 12.5 volts, add electrical loads by turn-
ing on electrical accessories until the system voltage
drops below 12.5 volts.
(a) If the clutch coil current reading is four
amperes or more, the coil is shorted and should be
replaced.
(b) If the clutch coil current reading is zero, the
coil is open and should be replaced.
Fig. 4 COMPRESSOR CLUTCH - TYPICAL
1 - CLUTCH PLATE
2 - SHAFT KEY
3 - PULLEY
4 - COIL
5 - CLUTCH SHIMS
6 - SNAP RING
7 - SNAP RING
WJCONTROLS 24 - 13

HVAC HOUSING
REMOVAL
The HVAC housing assembly must be removed
from the vehicle and the two halves of the housing
separated for service access of the heater core, evap-
orator coil, blend door(s), and each of the various
mode doors.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN AN ACCIDENTAL
AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN PLUMBING BEFORE PERFORMING THE
FOLLOWING OPERATION. (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - WARNING) (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMBING -
CAUTION)
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the instrument panel from the vehi-
cle(Refer to 23 - BODY/INSTRUMENT PANEL -
REMOVAL).
(3) Recover the refrigerant from the refrigerant
system. (Refer to 24 - HEATING & AIR CONDI-
TIONING/PLUMBING - STANDARD PROCEDURE -
REFRIGERANT RECOVERY)
(4) Disconnect the liquid line refrigerant line from
the evaporator inlet tube(Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING/LIQUID LINE -
REMOVAL) or (Refer to 24 - HEATING & AIR CON-
DITIONING/PLUMBING/LIQUID LINE - REMOV-
AL). Install plugs in, or tape over all of the opened
refrigerant line fittings.
(5) Disconnect the suction line refrigerant line
from the evaporator outlet tube(Refer to 24 - HEAT-
ING & AIR CONDITIONING/PLUMBING/SUCTION
LINE - REMOVAL), (Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING/SUCTION LINE -
REMOVAL) or (Refer to 24 - HEATING & AIR CON-
DITIONING/PLUMBING/SUCTION LINE - REMOV-
AL). Install plugs in, or tape over all of the opened
refrigerant line fittings.(6) Disconnect the heater hoses from the heater
core tubes. Clamp off the heater hoses to prevent loss
of coolant. Refer to Cooling for the procedures. Install
plugs in, or tape over the opened heater core tubes.
(7) If the vehicle is equipped with the manual tem-
perature control system, unplug the HVAC system
vacuum supply line connector from the tee fitting
near the heater core tubes.
(8) Remove the coolant reserve/overflow bottle
from the passenger side inner fender shield. Refer to
Cooling for the procedures.
(9) Remove the Powertrain Control Module (PCM)
from the passenger side dash panel in the engine
compartment and set it aside. Do not unplug the
PCM wire harness connectors. Refer to Electronic
Control Modules for the procedures.
(10) Remove the nuts from the HVAC housing
mounting studs on the engine compartment side of
the dash panel (Fig. 9).
(11) Remove the rear floor heat ducts from the
floor heat duct outlets (Fig. 10).
(12) Unplug the HVAC housing wire harness con-
nectors.
(13) Remove the HVAC housing mounting nuts
from the studs on the passenger compartment side of
the dash panel (Fig. 11).
Fig. 9 HVAC Housing - (rear view)
1 - Instrument Panel
2 - Air Intake
3 - Expansion Valve
4 - HVAC Housing
5 - Heater Core Input/Output Ports
6 - Instrument Panel Wiring Harness
7 - Blower Motor
WJDISTRIBUTION 24 - 41

NOTE: The blend door sub-assembly is attached to
the housing with 2 screws, and may be removed for
service (Fig. 19).
ASSEMBLY
(1) Place the top half of the HVAC housing on the
bottom half. Be certain that each of the door pivot
pins align with the pivot holes in the HVAC housing.
(2) Install the 10 screws that secure the two hous-
ing halves to each other. Tighten the HVAC housing
screws to 2.2 N´m (20 in. lbs.).
(3) Attach the wire harness electrical connector(s)
to the mounts on the lower case at the blower motor
end of the unit.
(4) Install the 5 clips that secure the two housing
halves to each other. Check doors for binding after
replacement, and after assembly of housing.
(5) Install the screw with plastic washer holding
the lever assembly to the upper case section.
(6) Install the mode door actuator on the left side
of the housing.
INSTALLATION
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN PLUMBING BEFORE PERFORMING THE
FOLLOWING OPERATION. (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - WARNING) (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMBING -
CAUTION)Any kinks or sharp bends in the refrigerant plumb-
ing will reduce the capacity of the entire air condi-
tioning system. Kinks and sharp bends reduce the
flow of refrigerant in the system. A good rule for the
flexible hose refrigerant lines is to keep the radius of
all bends at least ten times the diameter of the hose.
In addition, the flexible hose refrigerant lines should
be routed so they are at least 80 millimeters (3
inches) from the exhaust manifold.
High pressures are produced in the refrigerant sys-
tem when the air conditioning compressor is operat-
ing. Extreme care must be exercised to make sure
that each of the refrigerant system connections is
pressure-tight and leak free. It is a good practice to
inspect all flexible hose refrigerant lines at least once
a year to make sure they are in good condition and
properly routed.
(1) Position the HVAC housing to the dash panel.
Be certain that the evaporator condensate drain tube
and the housing mounting studs are inserted into
their correct mounting holes.
(2) Install the HVAC housing mounting nuts to the
studs on the passenger compartment side of the dash
panel. Tighten the nuts to 4.5 N´m (40 in. lbs.).
(3) Connect the HVAC housing wire harness con-
nectors.
(4) Reinstall the rear floor heat ducts to the center
floor heat duct outlets.
(5) Install and tighten the nuts onto the HVAC
housing mounting studs on the engine compartment
side of the dash panel. Tighten the nuts to 7 N´m (60
in. lbs.).
(6) Reinstall the PCM to the passenger side dash
panel in the engine compartment. Refer to Electronic
Control Modules for the procedures.
(7) Reinstall the coolant reserve/overflow bottle to
the passenger side inner fender shield. Refer to Cool-
ing for the procedures.
(8) If the vehicle is equipped with the manual tem-
perature control system, connect the HVAC system
vacuum supply line connector to the tee fitting near
the heater core tubes.
(9) Unclamp/unplug the heater core hoses and
tubes. Connect the heater hoses to the heater core
tubes and fill the engine cooling system. Refer to
Cooling for the procedures.
(10) Unplug or remove the tape from the suction
line and the evaporator outlet tube fittings. Connect
the suction line to the evaporator outlet tube.
Tighten retaining nut to 28 N´m (250 in. lbs.).
(11) Unplug or remove the tape from the liquid
line and the evaporator inlet tube fittings. Connect
the liquid line to the evaporator inlet tube. Tighten
retaining nut to 28 N´m (250 in. lbs.).
(12) Evacuate the refrigerant system. (Refer to 24
- HEATING & AIR CONDITIONING/PLUMBING -
Fig. 19 BLEND DOOR SUB-ASSEMBLY (AZC)
1 - PASSENGER SIDE BLEND DOOR
2 - BLEND DOOR SUB-ASSEMBLY
3 - DOOR PIVOT SHAFT BUSHING
4 - DOOR SHAFT LEVER
5 - DRIVER SIDE BLEND DOOR
WJDISTRIBUTION 24 - 45
HVAC HOUSING (Continued)

(M)Malfunction Indicator Lamp (MIL) illuminated during engine operation if this DTC was recorded
(depending if required by CARB and/or EPA). MIL is displayed as an engine icon on instrument panel.
(G)Generator lamp illuminated
Generic Scan
Tool P-CodeDRB Scan Tool Display Brief Description of DTC
P1687 No MIC BUS Message (No Cluster
BUS Message)No CCD/J1850 messages received from the Mechanical
Instrument Cluster (MIC) module.
P1688 (M) Internal Fuel Injection Pump
Controller FailureInternal problem within the fuel injection pump. Low
power, engine derated, or engine stops.
P1689 (M) No Communication Between ECM
and Injection Pump ModuleData link circuit failure between ECM and fuel injection
pump. Low power, engine derated, or engine stops.
P1690 (M) Fuel Injection Pump CKP Sensor
Does Not Agree With ECM CKP
SensorProblem in fuel sync signal. Possible injection pump
timing problem. Low power, engine derated, or engine
stops.
P1691 Fuel Injection Pump Controller
Calibration ErrorInternal fuel injection pump failure. Low power, engine
derated, or engine stops.
P1692 DTC Set In ECM A9Companion DTC9was set in both the ECM and PCM.
P1693 (M) DTC Detected in Companion Module A fault has been generated in the companion engine
control module.
P1693 (M) DTC Detected in PCM/ECM or DTC
Detected in ECMA9Companion DTC9was set in both the ECM and PCM.
P1694 Fault In Companion Module No CCD/J1850 messages received from the powertrain
control module-Aisin transmission
P1694 (M) No BUS (CCD) Messages received
from ECMBus communication failure to PCM.
P1695 No CCD/J1850 Message From Body
Control ModuleNo CCD/J1850 messages received from the body control
module.
P1696 PCM Failure EEPROM Write Denied Unsuccessful attempt to write to an EEPROM location by
the control module.
P1697 PCM Failure SRI Mile Not Stored Unsuccessful attempt to update Service Reminder
Indicator (SRI or EMR) mileage in the control module
EEPROM.
P1698 No CCD/J1850 Message From TCM No CCD/J1850 messages received from the electronic
transmission control module (EATX) or the Aisin
transmission controller.
P1698 No CCD Messages received from
PCMBus communication failure to PCM. A9Companion DTC9
was set in both the ECM and PCM.
P1699 No Climate Control Bus Messages
P1719 Skip Shift Solenoid Circuit An open or shorted condition detected in the transmission
2-3 gear lock-out solenoid control circuit.
P1740 TCC or OD Sol Perf A rationality error has been detected in either the TCC
solenoid or overdrive solenoid systems.
P1740 (M) TCC OR O/D Solenoid Performance Problem detected in transmission convertor clutch and/or
overdrive circuits (diesel engine with 4-speed auto. trans.
only).
WJEMISSIONS CONTROL 25 - 15
EMISSIONS CONTROL (Continued)