width JEEP LIBERTY 2002 KJ / 1.G Workshop Manual

STANDARD PROCEDURE
STANDARD PROCEDURE - HEIGHT
MEASUREMENT
RIDE HEIGHT
NOTE: The suspension is non-adjustable.
The vehicle suspension height should be measured
before performing wheel alignment procedure. Also
when front suspension components have been
replaced. This measure must be performed with the
vehicle supporting it's own weight and taken on both
sides of the vehicle.
Front and rear ride heights are not adjustable. The
spring selections at assembly determine ride height
for acceptable appearance of the vehicle. Ride height
dimensions assume full fluids (including fuel) and
zero passengers. Refer to the table below for front
ride height dimensions.
Vehicle ride height audits should be performed uti-
lizing the following procedure:
(1) Drive the vehicle straight and forward on a
non-tacky surface for a minimum of 20 feet to neu-
tralize track width.
(2) Bounce the front of the vehicle five times.
(3) Measure and record the dimensions
FRONT RIDE HEIGHT Front ride height is
defined by the relative vertical distance between the
spindle center line and the rear pivot point of the
front lower control arm to cradle attachment. The
spindle center line is to be measured at the outer
wheel face (point A). The rear pivot point is to be
measured at the center of the cam bolt (point B) at
its rearward most end (nut end). (Fig. 2)REAR RIDE HEIGHT Rear ride height is defined
by the relative vertical distance between the top of
the lower spring seat strike surface and the bottom
of the jounce cup (true metal to metal jounce travel).
This is to be measured vertically inside the coil from
the point intersecting the inboard edge and the for/
aft center of the jounce cup (point C) down to the
strike surface (point D). (Fig. 3)
Measurement Target Minimum Maximum
Front Ride
Height
Distance AB48.8 mm
Z=996.81
- 948.0338.8mm 58.8mm
Front Cross
Ride Height
Left - Right0.0 mm -10.0 mm 10.0 mm
Rear Ride
Height
Distance CD116.1 mm 106.1 mm 126.1 mm
Rear Cross
Ride Height
Left - Right0.0 mm -10.0 mm 10.0 mm
Fig. 2 FRONT RIDE HEIGHT MESUREMENT
1 - POINT - A
2 - POINT - B
Fig. 3 REAR RIDE HEIGHT MEASUREMENT
1 - POINT - C
2 - POINT - D
2 - 4 WHEEL ALIGNMENTKJ
WHEEL ALIGNMENT (Continued)

Examine the lining contact pattern to determine if
the shoes are bent or the drum is tapered. The lining
should exhibit contact across its entire width. Shoes
exhibiting contact only on one side should be
replaced and the drum checked for runout or taper.
Inspect the adjuster screw assembly. Replace the
assembly if the star wheel or threads are damaged,
or the components are severely rusted or corroded.
Discard the brake springs and retainer components
if worn, distorted or collapsed. Also replace the
springs if a brake drag condition had occurred. Over-
heating will distort and weaken the springs.
Inspect the brake shoe contact pads on the support
plate, replace the support plate if any of the pads are
worn or rusted through. Also replace the plate if it is
bent or distorted.
(1) Clean support plate with brake cleaner.
(2) If new drums are being installed, remove pro-
tective coating with carburetor cleaner followed by
final rinse with brake cleaner.
(3) Clean and lubricate anchor pin with light coat
of Mopar multi-mileage grease.
(4) Apply Mopar multi-mileage grease to brake
shoe contact surfaces of support plate (Fig. 10).
(5) Lubricate the adjuster screw threads and pivot
with spray lube.
(6) Attach parking brake lever to secondary brake
shoe. Use new washer and U-clip to secure lever.
(7) Attach the parking brake cable to lever (if
removed).
(8) Install the brake shoes on support plate.
Secure shoes with new hold-down springs, pins and
retainers.
(9) Install the parking brake strut and spring.(10) Install the guide plate and adjuster cable on
anchor pin.
(11) Install the adjuster cable guide on the shoe.
(12) Install the primary and secondary return
springs.
(13) Lubricate and assemble adjuster screw.
(14) Install the adjuster screw, spring and lever
and connect to adjuster cable.
(15) Adjust the shoes to the drum (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/BRAKE
PADS/SHOES - ADJUSTMENTS).
(16) Install the brake drum.
(17) Install the wheel/tire assemblies and lower
vehicle (Refer to 22 - TIRES/WHEELS/WHEELS -
STANDARD PROCEDURE).
(18) Verify firm brake pedal before moving vehicle.
ADJUSTMENTS
ADJUSTMENT - REAR DRUM BRAKE
The rear drum brakes are equipped with a self-ad-
justing mechanism. Under normal circumstances, the
only time adjustment is required is when the shoes
are replaced, removed for access to other parts, or
when one or both drums are replaced.
Adjustment can be made with a standard brake
gauge or with adjusting tool. Adjustment is per-
formed with the complete brake assembly installed
on the backing plate.
ADJUSTMENT WITH BRAKE GAUGE
(1) Be sure parking brakes are fully released.
(2) Raise rear of vehicle and remove wheels and
brake drums.
(3) Verify that left and right automatic adjuster
levers and cables are properly connected.
(4) Insert brake gauge in drum. Expand gauge
until gauge inner legs contact drum braking surface.
Then lock gauge in position (Fig. 11).
(5) Reverse gauge and install it on brake shoes.
Position gauge legs at shoe centers as shown (Fig.
12). If gauge does not fit (too loose/too tight), adjust
shoes.
(6) Pull shoe adjuster lever away from adjuster
screw star wheel.
(7) Turn adjuster screw star wheel (by hand) to
expand or retract brake shoes. Continue adjustment
until gauge outside legs are light drag-fit or 30 thou-
sands of an inch clearence on the shoes.
(8) Install brake drums and wheels and lower
vehicle.
(9) Drive vehicle and make one forward stop fol-
lowed by one reverse stop. Repeat procedure 8-10
times to operate automatic adjusters and equalize
adjustment.
Fig. 10 Shoe Contact Surfaces
1 - ANCHOR PIN
2 - SUPPORT PLATE
3 - SHOE CONTACT SURFACES
5 - 12 BRAKES - BASEKJ
BRAKE PADS / SHOES (Continued)

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)

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.
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-width²Spark-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. 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 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. 3).
Fig. 1 ENGINE BLOCK HEATER 2.4L
1 - CORE HOLE
2 - BLOCK HEATER
3 - POWER CORD
Fig. 2 ECT AND UPPER TIMING BELT COVER/
BOLTS-2.4L
1 - UPPER TIMING BELT COVER
2 - ELECTRICAL CONNECTOR (ECT)
3 - MOUNTING BOLTS (3)
KJENGINE7s-21
ENGINE BLOCK HEATER - 2.4L (Continued)

NOTE: Before replacing a Body Control Module
(BCM), use a DRBIIITscan tool to retrieve the cur-
rent settings for the BCM programmable features
and the axle ratio/tire size (electronic pinion factor).
Refer to the appropriate diagnostic information.
These settings should be duplicated in the replace-
ment BCM using the DRBIIITscan tool before
returning the vehicle to service.
(1) If the vehicle is equipped with the optional
Remote Keyless Entry (RKE) system, reinstall the
RKE module into the receptacle on the BCM. (Refer
to 8 - ELECTRICAL/POWER LOCKS/REMOTE KEY-
LESS ENTRY MODULE - INSTALLATION).
(2) Position the BCM onto the Junction Block (JB)
(Fig. 3).
(3) Install and tighten the four screws that secure
the BCM to the JB. Tighten the screws to 2 N´m (18
in. lbs.).
(4) Reinstall the Junction Block Module (JBM)
onto the instrument panel end bracket on the driver
side of the vehicle. (Refer to 8 - ELECTRICAL/
POWER DISTRIBUTION/JUNCTION BLOCK -
INSTALLATION).
(5) Reconnect the battery negative cable.
COMMUNICATION
DESCRIPTION
The DaimlerChrysler Programmable Communica-
tion Interface (PCI) data bus system is a single wire
multiplex system used for vehicle communications on
many DaimlerChrysler Corporation vehicles. Multi-
plexing is a system that enables the transmission of
several messages over a single channel or circuit. All
DaimlerChrysler vehicles use this principle for com-
munication between various microprocessor-based
electronic control modules. The PCI data bus exceeds
the Society of Automotive Engineers (SAE) J1850
Standard for Class B Multiplexing.
Many of the electronic control modules in a vehicle
require information from the same sensing device. In
the past, if information from one sensing device was
required by several controllers, a wire from each con-
troller needed to be connected in parallel to that sen-
sor. In addition, each controller utilizing analog
sensors required an Analog/Digital (A/D) converter in
order to9read9these sensor inputs. Multiplexing
reduces wire harness complexity, sensor current
loads and controller hardware because each sensing
device is connected to only one controller, which
reads and distributes the sensor information to the
other controllers over the data bus. Also, because
each controller on the data bus can access the con-
troller sensor inputs to every other controller on the
data bus, more function and feature capabilities are
possible.
In addition to reducing wire harness complexity,
component sensor current loads and controller hard-
ware, multiplexing offers a diagnostic advantage. A
multiplex system allows the information flowing
between controllers to be monitored using a diagnos-
tic scan tool. The DaimlerChrysler system allows an
electronic control module to broadcast message data
out onto the bus where all other electronic control
modules can9hear9the messages that are being sent.
When a module hears a message on the data bus
that it requires, it relays that message to its micro-
processor. Each module ignores the messages on the
data bus that are being sent to other electronic con-
trol modules.
OPERATION
Data exchange between modules is achieved by
serial transmission of encoded data over a single wire
broadcast network. The wire colors used for the PCI
data bus circuits are yellow with a violet tracer, or
violet with a yellow tracer, depending upon the appli-
cation. The PCI data bus messages are carried over
the bus in the form of Variable Pulse Width Modu-
lated (VPWM) signals. The PCI data bus speed is an
average 10.4 Kilo-bits per second (Kbps). By compar-
Fig. 3 Body Control Module Remove/Install
1 - SCREW (4)
2 - RKE MODULE
3 - BODY CONTROL MODULE
4 - JUNCTION BLOCK
8E - 8 ELECTRONIC CONTROL MODULESKJ
BODY CONTROL MODULE (Continued)

ison, the prior two-wire Chrysler Collision Detection
(CCD) data bus system is designed to run at 7.8125
Kbps.
The voltage network used to transmit messages
requires biasing and termination. Each module on
the PCI data bus system provides its own biasing
and termination. Each module (also referred to as a
node) terminates the bus through a terminating
resistor and a terminating capacitor. There are two
types of nodes on the bus. The dominant node termi-
nates the bus througha1KWresistor and a 3300 pF
capacitor. The Powertrain Control Module (PCM) is
the only dominant node for the PCI data bus system.
A standard node terminates the bus through an 11
KW resistor and a 330 pF capacitor.
The modules bias the bus when transmitting a
message. The PCI bus uses low and high voltage lev-
els to generate signals. Low voltage is around zero
volts and the high voltage is about seven and one-
half volts. The low and high voltage levels are gener-
ated by means of variable-pulse width modulation to
form signals of varying length. The Variable Pulse
Width Modulation (VPWM) used in PCI bus messag-
ing is a method in which both the state of the bus
and the width of the pulse are used to encode bit
information. A9zero9bit is defined as a short low
pulse or a long high pulse. A9one9bit is defined as a
long low pulse or a short high pulse. A low (passive)
state on the bus does not necessarily mean a zero bit.
It also depends upon pulse width. If the width is
short, it stands for a zero bit. If the width is long, it
stands for a one bit. Similarly, a high (active) state
does not necessarily mean a one bit. This too depends
upon pulse width. If the width is short, it stands for
a one bit. If the width is long, it stands for a zero bit.
In the case where there are successive zero or one
data bits, both the state of the bus and the width of
the pulse are changed alternately. This encoding
scheme is used for two reasons. First, this ensures
that only one symbol per transition and one transi-
tion per symbol exists. On each transition, every
transmitting module must decode the symbol on the
bus and begin timing of the next symbol. Since tim-
ing of the next symbol begins with the last transition
detected on the bus, all of the modules are re-syn-
chronized with each symbol. This ensures that thereare no accumulated timing errors during PCI data
bus communication.
The second reason for this encoding scheme is to
guarantee that the zero bit is the dominant bit on
the bus. When two modules are transmitting simul-
taneously on the bus, there must be some form of
arbitration to determine which module will gain con-
trol. A data collision occurs when two modules are
transmitting different messages at the same time.
When a module is transmitting on the bus, it is read-
ing the bus at the same time to ensure message
integrity. When a collision is detected, the module
that transmitted the one bit stops sending messages
over the bus until the bus becomes idle.
Each module is capable of transmitting and receiv-
ing data simultaneously. The typical PCI bus mes-
sage has the following four components:
²Message Header- One to three bytes in length.
The header contains information identifying the mes-
sage type and length, message priority, target mod-
ule(s) and sending module.
²Data Byte(s)- This is the actual message that
is being sent.
²Cyclic Redundancy Check (CRC) Byte- This
byte is used to detect errors during a message trans-
mission.
²In-Frame Response (IFR) byte(s)-Ifa
response is required from the target module(s), it can
be sent during this frame. This function is described
in greater detail in the following paragraph.
The IFR consists of one or more bytes, which are
transmitted during a message. If the sending module
requires information to be received immediately, the
target module(s) can send data over the bus during
the original message. This allows the sending module
to receive time-critical information without having to
wait for the target module to access the bus. After
the IFR is received, the sending module broadcasts
an End of Frame (EOF) message and releases control
of the bus.
The PCI data bus can be monitored using the
DRBIIItscan tool. It is possible, however, for the bus
to pass all DRBIIIttests and still be faulty if the
voltage parameters are all within the specified range
and false messages are being sent.
KJELECTRONIC CONTROL MODULES 8E - 9
COMMUNICATION (Continued)

POWERTRAIN CONTROL
MODULE
DESCRIPTION
DESCRIPTION - PCM
The Powertrain Control Module (PCM) is located
in the engine compartment (Fig. 8). The PCM is
referred to as JTEC.
DESCRIPTION - MODES OF OPERATION
As input signals to the Powertrain Control Module
(PCM) change, the PCM adjusts its response to the
output devices. For example, the PCM must calculate
different injector pulse width and ignition timing for
idle than it does for wide open throttle (WOT).
The PCM will operate in two different modes:
Open Loop and Closed Loop.
During Open Loop modes, the PCM receives input
signals and responds only according to preset PCM
programming. Input from the oxygen (O2S) sensors
is not monitored during Open Loop modes.
During Closed Loop modes, the PCM will monitor
the oxygen (O2S) sensors input. This input indicates
to the PCM whether or not the calculated injector
pulse width results in the ideal air-fuel ratio. This
ratio is 14.7 parts air-to-1 part fuel. By monitoring
the exhaust oxygen content through the O2S sensor,
the PCM can fine tune the injector pulse width. This
is done to achieve optimum fuel economy combined
with low emission engine performance.
The fuel injection system has the following modes
of operation:
²Ignition switch ON
²Engine start-up (crank)
²Engine warm-up
²Idle
²Cruise
²Acceleration
²Deceleration
²Wide open throttle (WOT)
²Ignition switch OFF
The ignition switch On, engine start-up (crank),
engine warm-up, acceleration, deceleration and wide
open throttle modes are Open Loop modes. The idle
and cruise modes, (with the engine at operating tem-
perature) are Closed Loop modes.
IGNITION SWITCH (KEY-ON) MODE
This is an Open Loop mode. When the fuel system
is activated by the ignition switch, the following
actions occur:
²The PCM pre-positions the idle air control (IAC)
motor.
²The PCM determines atmospheric air pressure
from the MAP sensor input to determine basic fuel
strategy.
²The PCM monitors the engine coolant tempera-
ture sensor input. The PCM modifies fuel strategy
based on this input.
²Intake manifold air temperature sensor input is
monitored.
²Throttle position sensor (TPS) is monitored.
²The auto shutdown (ASD) relay is energized by
the PCM for approximately three seconds.
Fig. 7 DATA LINK CONNECTOR LOCATION
Fig. 8 PCM LOCATION
KJELECTRONIC CONTROL MODULES 8E - 11
DATA LINK CONNECTOR (Continued)

²The fuel pump is energized through the fuel
pump relay by the PCM. The fuel pump will operate
for approximately three seconds unless the engine is
operating or the starter motor is engaged.
²The O2S sensor heater element is energized via
the ASD or O2S heater relay. The O2S sensor input
is not used by the PCM to calibrate air-fuel ratio dur-
ing this mode of operation.
ENGINE START-UP MODE
This is an Open Loop mode. The following actions
occur when the starter motor is engaged.
The PCM receives inputs from:
²Battery voltage
²Engine coolant temperature sensor
²Crankshaft position sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal
The PCM monitors the crankshaft position sensor.
If the PCM does not receive a crankshaft position
sensor signal within 3 seconds of cranking the
engine, it will shut down the fuel injection system.
The fuel pump is activated by the PCM through
the fuel pump relay.
Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then control
the injection sequence and injector pulse width by
turning the ground circuit to each individual injector
on and off.
The PCM determines the proper ignition timing
according to input received from the crankshaft posi-
tion sensor.
ENGINE WARM-UP MODE
This is an Open Loop mode. During engine warm-
up, the PCM receives inputs from:
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
Based on these inputs the following occurs:
²Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then control
the injection sequence and injector pulse width by
turning the ground circuit to each individual injector
on and off.²The PCM adjusts engine idle speed through the
idle air control (IAC) motor and adjusts ignition tim-
ing.
²The PCM operates the A/C compressor clutch
through the A/C compressor clutch relay. This is done
if A/C has been selected by the vehicle operator and
specified pressures are met at the high and low±pres-
sure A/C switches. Refer to Heating and Air Condi-
tioning for additional information.
²When engine has reached operating tempera-
ture, the PCM will begin monitoring O2S sensor
input. The system will then leave the warm-up mode
and go into closed loop operation.
IDLE MODE
When the engine is at operating temperature, this
is a Closed Loop mode. At idle speed, the PCM
receives inputs from:
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal
²Battery voltage
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
²Oxygen sensors
Based on these inputs, the following occurs:
²Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then control
injection sequence and injector pulse width by turn-
ing the ground circuit to each individual injector on
and off.
²The PCM monitors the O2S sensor input and
adjusts air-fuel ratio by varying injector pulse width.
It also adjusts engine idle speed through the idle air
control (IAC) motor.
²The PCM adjusts ignition timing by increasing
and decreasing spark advance.
²The PCM operates the A/C compressor clutch
through the A/C compressor clutch relay. This is done
if A/C has been selected by the vehicle operator and
specified pressures are met at the high and low±pres-
sure A/C switches. Refer to Heating and Air Condi-
tioning for additional information.
CRUISE MODE
When the engine is at operating temperature, this
is a Closed Loop mode. At cruising speed, the PCM
receives inputs from:
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
8E - 12 ELECTRONIC CONTROL MODULESKJ
POWERTRAIN CONTROL MODULE (Continued)

²Battery voltage
²Engine coolant temperature sensor
²Crankshaft position sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
²Oxygen (O2S) sensors
Based on these inputs, the following occurs:
²Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then adjust
the injector pulse width by turning the ground circuit
to each individual injector on and off.
²The PCM monitors the O2S sensor input and
adjusts air-fuel ratio. It also adjusts engine idle
speed through the idle air control (IAC) motor.
²The PCM adjusts ignition timing by turning the
ground path to the coil(s) on and off.
²The PCM operates the A/C compressor clutch
through the clutch relay. This happens if A/C has
been selected by the vehicle operator and requested
by the A/C thermostat.
ACCELERATION MODE
This is an Open Loop mode. The PCM recognizes
an abrupt increase in throttle position or MAP pres-
sure as a demand for increased engine output and
vehicle acceleration. The PCM increases injector
pulse width in response to increased throttle opening.
DECELERATION MODE
When the engine is at operating temperature, this
is an Open Loop mode. During hard deceleration, the
PCM receives the following inputs.
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
²Battery voltage
²Engine coolant temperature sensor
²Crankshaft position sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
²Vehicle speed
If the vehicle is under hard deceleration with the
proper rpm and closed throttle conditions, the PCM
will ignore the oxygen sensor input signal. The PCM
will enter a fuel cut-off strategy in which it will not
supply a ground to the injectors. If a hard decelera-
tion does not exist, the PCM will determine the
proper injector pulse width and continue injection.Based on the above inputs, the PCM will adjust
engine idle speed through the idle air control (IAC)
motor.
The PCM adjusts ignition timing by turning the
ground path to the coil on and off.
WIDE OPEN THROTTLE MODE
This is an Open Loop mode. During wide open
throttle operation, the PCM receives the following
inputs.
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal
During wide open throttle conditions, the following
occurs:
²Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then control
the injection sequence and injector pulse width by
turning the ground circuit to each individual injector
on and off. The PCM ignores the oxygen sensor input
signal and provides a predetermined amount of addi-
tional fuel. This is done by adjusting injector pulse
width.
²The PCM adjusts ignition timing by turning the
ground path to the coil(s) on and off.
IGNITION SWITCH OFF MODE
When ignition switch is turned to OFF position,
the PCM stops operating the injectors, ignition coil,
ASD relay and fuel pump relay.
DESCRIPTION - 5 VOLT SUPPLIES
Two different Powertrain Control Module (PCM)
five volt supply circuits are used; primary and sec-
ondary.
DESCRIPTION - IGNITION CIRCUIT SENSE
This circuit ties the ignition switch to the Power-
train Control Module (PCM).
DESCRIPTION - POWER GROUNDS
The Powertrain Control Module (PCM) has 2 main
grounds. Both of these grounds are referred to as
power grounds. All of the high-current, noisy, electri-
cal devices are connected to these grounds as well as
all of the sensor returns. The sensor return comes
into the sensor return circuit, passes through noise
suppression, and is then connected to the power
ground.
The power ground is used to control ground cir-
cuits for the following PCM loads:
²Generator field winding
KJELECTRONIC CONTROL MODULES 8E - 13
POWERTRAIN CONTROL MODULE (Continued)

²Fuel injectors
²Ignition coil(s)
²Certain relays/solenoids
²Certain sensors
DESCRIPTION - SENSOR RETURN
The Sensor Return circuits are internal to the Pow-
ertrain Control Module (PCM).
Sensor Return provides a low±noise ground refer-
ence for all engine control system sensors. Refer to
Power Grounds for more information.
OPERATION
OPERATION - PCM
The PCM operates the fuel system. The PCM is a
pre-programmed, triple microprocessor digital com-
puter. It regulates ignition timing, air-fuel ratio,
emission control devices, charging system, certain
transmission features, speed control, air conditioning
compressor clutch engagement and idle speed. The
PCM can adapt its programming to meet changing
operating conditions.
The PCM receives input signals from various
switches and sensors. Based on these inputs, the
PCM regulates various engine and vehicle operations
through different system components. These compo-
nents are referred to as Powertrain Control Module
(PCM) Outputs. The sensors and switches that pro-
vide inputs to the PCM are considered Powertrain
Control Module (PCM) Inputs.
The PCM adjusts ignition timing based upon
inputs it receives from sensors that react to: engine
rpm, manifold absolute pressure, engine coolant tem-
perature, throttle position, transmission gear selec-
tion (automatic transmission), vehicle speed, power
steering pump pressure, and the brake switch.
The PCM adjusts idle speed based on inputs it
receives from sensors that react to: throttle position,
vehicle speed, transmission gear selection, engine
coolant temperature and from inputs it receives from
the air conditioning clutch switch and brake switch.
Based on inputs that it receives, the PCM adjusts
ignition coil dwell. The PCM also adjusts the gener-
ator charge rate through control of the generator
field and provides speed control operation.
NOTE: PCM Inputs:
²A/C request (if equipped with factory A/C)
²A/C select (if equipped with factory A/C)
²A/C pressure transducer
²Auto shutdown (ASD) sense
²Battery temperature
²Battery voltage
²Brake switch²J1850 bus (+) circuits
²J1850 bus (-) circuits
²Camshaft position sensor signal
²Crankshaft position sensor
²Data link connection for DRB scan tool
²Engine coolant temperature sensor
²Fuel level (through J1850 circuitry)
²Generator (battery voltage) output
²Ignition circuit sense (ignition switch in on/off/
crank/run position)
²Intake manifold air temperature sensor
²Knock sensors (2 on 3.7L engine)
²Leak detection pump (switch) sense (if equipped)
²Manifold absolute pressure (MAP) sensor
²Oil pressure
²Oxygen sensors
²Park/neutral switch (auto. trans. only)
²Power ground
²Power steering pressure switch
²Sensor return
²Signal ground
²Speed control multiplexed single wire input
²Throttle position sensor
²Transfer case switch (4WD range position)
²Vehicle speed sensor
NOTE: PCM Outputs:
²A/C clutch relay
²Auto shutdown (ASD) relay
²J1850 bus (+/-) circuits for: speedometer, voltme-
ter, fuel gauge, oil pressure gauge/lamp, engine temp.
gauge and speed control warn. lamp
²Clutch pedal position switch override relay
²Data link connection for DRB scan tool
²EGR valve control solenoid (if equipped)
²EVAP canister purge solenoid
²Five volt sensor supply (primary)
²Five volt sensor supply (secondary)
²Fuel injectors
²Fuel pump relay
²Generator field driver (-)
²Generator field driver (+)
²Idle air control (IAC) motor
²Ignition coil(s)
²Leak detection pump (if equipped)
²Malfunction indicator lamp (Check engine lamp).
Driven through J1850 circuits.
²Oxygen sensor heater relays
²Oxygen sensors (pulse width modulated)
²Radiator cooling fan relay (pulse width modu-
lated)
²Speed control vacuum solenoid
²Speed control vent solenoid
²Tachometer (if equipped). Driven through J1850
circuits.
8E - 14 ELECTRONIC CONTROL MODULESKJ
POWERTRAIN CONTROL MODULE (Continued)