Injector wiring JEEP GRAND CHEROKEE 2002 WJ / 2.G Workshop Manual

BCM programming then performs those tasks and
provides features through both PCI data bus commu-
nication with other electronic modules and hard
wired outputs to a number of relays. These relays
provide the BCM with the ability to control numer-
ous high current accessory systems in the vehicle.
The BCM circuitry operates on battery current
received through fuses in the Junction Block (JB) on a
non-switched fused B(+) circuit, a fused ignition switch
output (start-run) circuit, and a fused ignition switch
output (run-accessory) circuit. This arrangement allows
the BCM to provide some features regardless of the
ignition switch position. The BCM circuitry is grounded
through the chassis beneath the center console.
The BCM monitors its own internal circuitry as
well as many of its input and output circuits, and
will store a Diagnostic Trouble Code (DTC) in elec-
tronic memory for any failure it detects. These DTCs
can be retrieved and diagnosed using a DRBIIItscan
tool. Refer to the appropriate diagnostic information.
HARD WIRED INPUTS
The hard wired inputs to the BCM include the fol-
lowing:
²A/C switch signal
²Ambient temperature sensor signal
²Body control module flash enable
²Coolant level switch sense
²Door ajar switch sense (two circuits - one left
rear, and one right rear)
²Driver seat heater switch mux
²Fog lamp switch sense
²Fused B(+)
²Fused ignition switch output (run-acc)
²Fused ignition switch output (st-run)
²Ground (five circuits - two Z1, and three Z2)
²Hazard switch sense
²Headlamp switch mux
²High beam switch sense
²Hood ajar switch sense (export)
²Key-in ignition switch sense
²Liftgate ajar switch sense
²Liftgate courtesy disable
²Liftgate flip-up ajar switch sense
²Panel lamps dimmer signal
²Park lamp relay output
²Passenger seat heater switch mux
²PCI bus
²Radio control mux
²Rear window defogger switch sense
²Seat belt switch sense
²Ultralight sensor signal
²Washer fluid switch sense
²Washer pump switch sense
²Windshield wiper switch mux
²Wiper park switch sense
MESSAGING
The BCM uses the following messages received
from other electronic modules over the PCI data bus:
²Accessory Delay Control (DDM/PDM)
²Battery Temperature (PCM)
²Chime Request (EMIC, EVIC, SKIM)
²Cylinder Lock Switch Status (DDM)
²Door Ajar Status/Front Doors (DDM/PDM)
²Door Lock Status (DDM/PDM)
²Engine Model (PCM)
²Engine RPM (PCM)
²Engine Temperature (PCM)
²English/Metric Default (EMIC)
²Fuel Tank Level (PCM)
²Fuel Used/Injector Pulses (PCM)
²Panic Control (PDM)
²Programmable Features Preferences/Audible &
Optical Chirps/Headlamp Delay (EVIC)
²RKE Status (PDM)
²Vehicle Identification Number (PCM)
²Vehicle Speed (PCM)
The BCM provides the following messages to other
electronic modules over the PCI data bus:
²A/C Switch Status (PCM)
²Ambient Temperature Data (AZC/EVIC/PCM)
²Average/Instantaneous Fuel Economy (EVIC)
²Country Code (EMIC)
²Courtesy Lamp Status (DDM/PDM)
²Distance To Empty (EVIC)
²Elapsed Ignition On Timer (EVIC)
²English/Metric Status (EMIC)
²Front & Rear Door Ajar Status (EVIC)
²Front & Rear Fog Lamp Status (EMIC)
²Heated Seat Switch Status (HSM/MHSM)
²High Beam Status (EMIC)
²Ignition Off Timer (EVIC)
²Ignition Switch Position (DDM/PDM)
²Key-In Ignition Status (DDM/PDM)
²Low Beam Status (EMIC)
²Panel Lamp Status (AZC/EMIC/Radio)
²Rear Window Defogger Relay Status (DDM/
PDM)
²Remote Radio Switch Status (Radio)
²Seatbelt Status (EMIC/MHSM/MSM)
DIAGNOSIS AND TESTING - BODY CONTROL
MODULE
The hard wired inputs to and outputs from the
Body Control Module (BCM) may be diagnosed and
tested using conventional diagnostic tools and proce-
dures. Refer to the appropriate wiring information.
Conventional diagnostic methods may not prove
conclusive in the diagnosis of the BCM. In order to
obtain conclusive testing of the BCM, the Program-
mable Communications Interface (PCI) data bus net-
work and all of the electronic modules that provide
8E - 4 ELECTRONIC CONTROL MODULESWJ
BODY CONTROL MODULE (Continued)

INSTALLATION
(1) Install the MHSM,HSM into the bracket.
(2) Position the heated seat module and mounting
bracket onto the power seat track.
(3) Reconnect the power seat wiring harness con-
nectors to the heated seat module.
(4) Install the driver side front bucket seat onto
the power seat track unit (Refer to 23 - BODY/
SEATS/SEAT TRACK ADJUSTER - INSTALLA-
TION).
(5) Reconnect the battery negative cable.
NOTE: If the vehicle is equipped with the optional
Memory System, following installation, it will be
necessary to initialize the Memory Heated Seat
Module (MHSM). In order to function properly, the
MHSM must ªlearnº the sensor values of each of
the power seat motor position transducers in each
of the adjuster hard stop positions. This is done by
performing the ªReset Guard Bandº procedure
using a DRBIIITscan tool and the proper Diagnostic
Procedures manual.
WARNING: THE ªRESET GUARD BANDº PROCE-
DURE WILL CAUSE THE DRIVER SIDE FRONT
SEAT TO AUTOMATICALLY ADJUST TO EACH OF
ITS TRAVEL LIMITS. BE CERTAIN THAT NO ONE IS
SEATED IN THE VEHICLE AND THAT THERE IS
NOTHING IN THE VEHICLE THAT WILL OBSTRUCT
SEAT MOVEMENT. FAILURE TO OBSERVE THIS
WARNING COULD RESULT IN PERSONAL INJURIES
AND/OR VEHICLE DAMAGE.
POWERTRAIN CONTROL
MODULE
DESCRIPTION
DESCRIPTION - PCM
The Powertrain Control Module (PCM) is located
in the engine compartment (Fig. 11). The PCM is
referred to as JTEC.
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 PCMprogramming. 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:
Fig. 11 PCM Location
1 - PCM
2 - COOLANT TANK
8E - 12 ELECTRONIC CONTROL MODULESWJ
MEMORY HEATED SEAT/MIRROR MODULE (Continued)

CAUTION: The left and right fuel rails are replaced
as an assembly. Do not attempt to separate rail
halves at connector tube (Fig. 22). Due to design of
tube, it does not use any clamps. Never attempt to
install a clamping device of any kind to tube. When
removing fuel rail assembly for any reason, be care-
ful not to bend or kink tube.
(1) Remove fuel tank filler tube cap.
(2) Perform Fuel System Pressure Release Proce-
dure.
(3) Remove negative battery cable at battery.
(4) Remove air duct at throttle body air box.
(5) Remove air box at throttle body.
(6) Remove wiring at rear of generator.
(7) Disconnect fuel line latch clip and fuel line at
fuel rail. A special tool will be necessary for fuel line
disconnection. Refer to Quick-Connect Fittings.
(8) Remove vacuum lines at throttle body.(9) Disconnect electrical connectors at all 8 fuel
injectors. To remove connector refer to (Fig. 23). Push
red colored slider away from injector (1). While push-
ing slider, depress tab (2) and remove connector (3)
from injector. The factory fuel injection wiring har-
ness is numerically tagged (INJ 1, INJ 2, etc.) for
injector position identification. If harness is not
tagged, note wiring location before removal.
(10) Disconnect electrical connectors at throttle
body.
(11) Disconnect electrical connectors at MAP and
IAT sensors.
Fig. 21 Fuel Injector Rail/Fuel DamperÐ4.0L Engine
1 - INJ. #1
2 - INJ. #2
3 - INJ. #3
4 - INJ. #4
5 - INJ. #5
6 - INJ. #6
7 - FUEL INJECTOR RAIL
8 - FUEL DAMPER
9 - PRESSURE TEST PORT CAP
10 - MOUNTING BOLTS (4)
11 - QUICK-CONNECT FITTING
Fig. 22 FUEL INJECTOR RAIL - 4.7L V-8 EN
1 - MOUNTING BOLTS (4)
2 - INJ.#7
3 - INJ.#5
4 - QUICK-CONNECT FITTING
5 - INJ.#3
6 - FUEL INJECTOR RAIL
7 - INJ.#1
8 - CONNECTOR TUBE
9 - INJ.#2
10 - INJ.#4
11 - INJ.#6
12 - INJ.#8
13 - PRESSURE TEST PORT CAP
14 - 16 FUEL DELIVERYWJ
FUEL RAIL (Continued)

(12) Remove first three ignition coils on each bank
(cylinders #1, 3, 5, 2, 4 and 6). Refer to Ignition Coil
Removal/Installation.
(13) Remove 4 fuel rail mounting bolts (Fig. 22).
(14) Gently rock and pullleftside of fuel rail until
fuel injectors just start to clear machined holes in
cylinder head. Gently rock and pullrightside of rail
until injectors just start to clear cylinder head holes.
Repeat this procedure (left/right) until all injectors
have cleared cylinder head holes.
(15) Remove fuel rail (with injectors attached)
from engine.
(16) If fuel injectors are to be removed, refer to
Fuel Injector Removal/Installation.
REMOVAL - 4.0L
The fuel damper is not serviced separately.
WARNING: THE FUEL SYSTEM IS UNDER CON-
STANT FUEL PRESSURE EVEN WITH ENGINE OFF.
THIS PRESSURE MUST BE RELEASED BEFORE
SERVICING FUEL RAIL.
(1) Remove fuel tank filler tube cap.
(2) Perform Fuel System Pressure Release Proce-
dure.
(3) Disconnect negative battery cable from battery.(4) Remove air tube at top of throttle body. Note:
Some engine/vehicles may require removal of air
cleaner ducts at throttle body.
(5) Disconnect electrical connectors at all 6 fuel
injectors. To remove connector refer to (Fig. 25). Push
red colored slider away from injector (1). While push-
ing slider, depress tab (2) and remove connector (3)
from injector. The factory fuel injection wiring har-
ness is numerically tagged (INJ 1, INJ 2, etc.) for
injector position identification. If harness is not
tagged, note wiring location before removal.
(6) Remove oxygen sensor wiring clip nuts at fuel
rail mounting studs (certain emissions packages
only).
(7) Disconnect fuel supply line latch clip and fuel
line at fuel rail. Refer to Quick-Connect Fittings.
(8) Disconnect throttle cable at throttle body. Refer
to Throttle Cable Removal/Installation.
Fig. 23 Remove/Install Injector ConnectorÐ4.7L V-8
Engine
Fig. 24 Fuel Rail MountingÐ4.0L Engine
1 - INJ. #1
2 - INJ. #2
3 - INJ. #3
4 - INJ. #4
5 - INJ. #5
6 - INJ. #6
7 - FUEL INJECTOR RAIL
8 - FUEL DAMPER
9 - PRESSURE TEST PORT CAP
10 - MOUNTING BOLTS (4)
11 - QUICK-CONNECT FITTING
WJFUEL DELIVERY 14 - 17
FUEL RAIL (Continued)

(9) Disconnect speed control cable at throttle body
(if equipped). Refer to Speed Control Cable.
(10) Disconnect automatic transmission cable at
throttle body (if equipped).
(11) Remove cable routing bracket at intake mani-
fold.
(12) Clean dirt/debris from each fuel injector at
intake manifold.
(13) Remove fuel rail mounting nuts/bolts (Fig.
24).
(14) Remove fuel rail by gently rocking until all
fuel injectors have cleared machined holes at intake
manifold.
(15) If fuel injectors are to be removed, refer to
Fuel Injector Removal/Installation.
INSTALLATION
INSTALLATION - 4.7L
(1) If fuel injectors are to be installed, refer to Fuel
Injector Removal/Installation.
(2) Apply a small amount of engine oil to each fuel
injector o-ring. This will help in fuel rail installation.
(3) Position fuel rail/fuel injector assembly to
machined injector openings in cylinder head.
(4) Guide each injector into cylinder head. Be care-
ful not to tear injector o-rings.(5) Pushrightside of fuel rail down until fuel
injectors have bottomed on cylinder head shoulder.
Pushleftfuel rail down until injectors have bot-
tomed on cylinder head shoulder.
(6) Install 4 fuel rail mounting bolts and tighten to
27 N´m (20 ft. lbs.).
(7) Install ignition coils. Refer to Ignition Coil
Removal/Installation.
(8) Connect electrical connectors to throttle body.
(9) Connect electrical connectors to MAP and IAT
sensors.
(10) Connect electrical connectors at all fuel injec-
tors. To install connector, refer to (Fig. 23). Push con-
nector onto injector (1) and then push and lock red
colored slider (2). Verify connector is locked to injec-
tor by lightly tugging on connector.
(11) Connect vacuum lines to throttle body.
(12) Connect fuel line latch clip and fuel line to
fuel rail. Refer to Quick-Connect Fittings.
(13) Connect wiring to rear of generator.
(14) Install air box to throttle body.
(15) Install air duct to air box.
(16) Connect battery cable to battery.
(17) Start engine and check for leaks.
INSTALLATION - 4.0L
(1) If fuel injectors are to be installed, refer to Fuel
Injector Removal/Installation.
(2) Clean each injector bore at intake manifold.
(3) Apply a small amount of clean engine oil to
each injector o-ring. This will aid in installation.
(4) Position tips of all fuel injectors into the corre-
sponding injector bore in intake manifold. Seat injec-
tors into manifold.
(5) Install and tighten fuel rail mounting bolts to
11  3 N´m (100  25 in. lbs.) torque.
(6) Connect electrical connectors at all fuel injec-
tors. To install connector, refer to (Fig. 25). Push con-
nector onto injector (1) and then push and lock red
colored slider (2). Verify connector is locked to injec-
tor by lightly tugging on connector.
(7) Connect fuel line and fuel line latch clip to fuel
rail. Refer Quick-Connect Fittings.
(8) Install protective cap to pressure test port fit-
ting (if equipped).
(9) Install cable routing bracket to intake mani-
fold.
(10) Connect throttle cable at throttle body.
(11) Connect speed control cable at throttle body (if
equipped).
(12) Connect automatic transmission cable at
throttle body (if equipped).
(13) Install oxygen sensor wiring clip nuts to fuel
rail mounting studs (certain emissions packages
only).
Fig. 25 Remove/Install Injector ConnectorÐ4.0L
Engine
14 - 18 FUEL DELIVERYWJ
FUEL RAIL (Continued)

The sensor is a hall effect device combined with an
internal magnet. It is also sensitive to steel within a
certain distance from it.
On 4.0L 6-cylinder engines, the flywheel/drive
plate has 3 sets of four notches at its outer edge (Fig.
19).
The notches cause a pulse to be generated when
they pass under the sensor. The pulses are the input
to the PCM. For each engine revolution there are 3
sets of four pulses generated.
The trailing edge of the fourth notch, which causes
the pulse, is four degrees before top dead center
(TDC) of the corresponding piston.
The engine will not operate if the PCM does not
receive a crankshaft position sensor input.
OPERATION - 4.7L
Engine speed and crankshaft position are provided
through the crankshaft position sensor. The sensor
generates pulses that are the input sent to the pow-
ertrain control module (PCM). The PCM interprets
the sensor input to determine the crankshaft posi-
tion. The PCM then uses this position, along with
other inputs, to determine injector sequence and igni-
tion timing.
The sensor is a hall effect device combined with an
internal magnet. It is also sensitive to steel within a
certain distance from it.On the 4.7L V±8 engine, a tonewheel is bolted to
the engine crankshaft (Fig. 20). This tonewheel has
sets of notches at its outer edge (Fig. 20).
The notches cause a pulse to be generated when
they pass under the sensor. The pulses are the input
to the PCM.
REMOVAL
REMOVAL - 4.0L
The Crankshaft Position (CKP) sensor is mounted
to the transmission bellhousing at the left/rear side
of the engine block (Fig. 21). The sensoris adjust-
ableand is attached with one bolt. A wire shield/
router is attached to the sensor (Fig. 21).
(1) Disconnect sensor pigtail harness (3±way con-
nector) from main engine wiring harness.
(2) Remove sensor mounting bolt.
(3) Remove wire shield and sensor.
REMOVAL - 4.7L
The Crankshaft Position (CKP) sensor is bolted to
the side of the engine cylinder block above the
starter motor (Fig. 22). It is positioned into a
machined hole at the side of the engine block.
(1) Remove starter motor. Refer to Starter Remov-
al/Installation.
Fig. 19 CKP Sensor OperationÐ4.0L 6-Cyl. Engine
1 - CRANKSHAFT POSITION SENSOR
2 - FLYWHEEL
3 - FLYWHEEL NOTCHES
Fig. 20 CKP Sensor Operation and TonewheelÐ4.7L
V±8 Engine
1 - TONEWHEEL
2 - NOTCHES
3 - CRANKSHAFT POSITION SENSOR
4 - CRANKSHAFT
WJFUEL INJECTION 14 - 41
CRANKSHAFT POSITION SENSOR (Continued)

(5) Push sensor against flywheel/drive plate. With
sensor pushed against flywheel/drive plate, tighten
mounting bolt to 7 N´m (60 in. lbs.) torque.
(6) Route sensor wiring harness into wire shield.
(7) Connect sensor pigtail harness electrical con-
nector to main wiring harness.
INSTALLATION - 4.7L
(1) Clean out machined hole in engine block.
(2) Apply a small amount of engine oil to sensor
o-ring.
(3) Install sensor into engine block with a slight
rocking action. Do not twist sensor into position as
damage to o-ring may result.
CAUTION: Before tightening sensor mounting bolt,
be sure sensor is completely flush to cylinder
block. If sensor is not flush, damage to sensor
mounting tang may result.
(4) Install mounting bolt and tighten to 28 N´m
(21 ft. lbs.) torque.
(5) Connect electrical connector to sensor.
(6) Install starter motor. Refer to Starter Removal/
Installation.
FUEL INJECTOR
DESCRIPTION
A separate fuel injector (Fig. 24) is used for each
individual cylinder.
OPERATION
OPERATION
The fuel injectors are electrical solenoids. The
injector contains a pintle that closes off an orifice at
the nozzle end. When electric current is supplied to
the injector, the armature and needle move a short
distance against a spring, allowing fuel to flow out
the orifice. Because the fuel is under high pressure, a
fine spray is developed in the shape of a pencil
stream. The spraying action atomizes the fuel, add-
ing it to the air entering the combustion chamber.
The top (fuel entry) end of the injector (Fig. 24) is
attached into an opening on the fuel rail.
The nozzle (outlet) ends of the injectors are posi-
tioned into openings in the intake manifold just
above the intake valve ports of the cylinder head.
The engine wiring harness connector for each fuel
injector is equipped with an attached numerical tag
(INJ 1, INJ 2 etc.). This is used to identify each fuel
injector.
The injectors are electrically energized, individu-
ally and in a sequential order by the Powertrain Con-
trol Module (PCM). The PCM will adjust injector
pulse width by switching the ground path to each
individual injector on and off. Injector pulse width is
the period of time that the injector is energized. The
PCM will adjust injector pulse width based on vari-
ous inputs it receives.
Battery voltage is supplied to the injectors through
the ASD relay.
The PCM determines injector pulse width based on
various inputs.
OPERATION - PCM OUTPUT
The nozzle ends of the injectors are positioned into
openings in the intake manifold just above the intake
valve ports of the cylinder head. The engine wiring
harness connector for each fuel injector is equipped
with an attached numerical tag (INJ 1, INJ 2 etc.).
This is used to identify each fuel injector with its
respective cylinder number.
The injectors are energized individually in a
sequential order by the Powertrain Control Module
(PCM). The PCM will adjust injector pulse width by
switching the ground path to each individual injector
on and off. Injector pulse width is the period of time
that the injector is energized. The PCM will adjust
injector pulse width based on various inputs it
receives.
Battery voltage (12 volts +) is supplied to the injec-
tors through the ASD relay. The ASD relay will shut-
down the 12 volt power source to the fuel injectors if
the PCM senses the ignition is on, but the engine is
not running. This occurs after the engine has not
been running for approximately 1.8 seconds.
Fig. 24 Fuel InjectorÐ4.0L/4.7L Engines
1 - FUEL INJECTOR
2 - NOZZLE
3 - TOP (FUEL ENTRY)
WJFUEL INJECTION 14 - 43
CRANKSHAFT POSITION SENSOR (Continued)

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)

In Closed Loop operation, the PCM monitors cer-
tain O2 sensor input(s) along with other inputs, and
adjusts the injector pulse width accordingly. During
Open Loop operation, the PCM ignores the O2 sensor
input. The PCM adjusts injector pulse width based
on preprogrammed (fixed) values and inputs from
other sensors.
Upstream Sensor (Non-California Emissions):
The upstream sensor (1/1) provides an input voltage
to the PCM. The input tells the PCM the oxygen con-
tent of the exhaust gas. The PCM uses this informa-
tion to fine tune fuel delivery to maintain the correct
oxygen content at the downstream oxygen sensor.
The PCM will change the air/fuel ratio until the
upstream sensor inputs a voltage that the PCM has
determined will make the downstream sensor output
(oxygen content) correct.
The upstream oxygen sensor also provides an input
to determine catalytic convertor efficiency.
Downstream Sensor (Non-California Emis-
sions):The downstream oxygen sensor (1/2) is also
used to determine the correct air-fuel ratio. As the
oxygen content changes at the downstream sensor,
the PCM calculates how much air-fuel ratio change is
required. The PCM then looks at the upstream oxy-
gen sensor voltage and changes fuel delivery until
the upstream sensor voltage changes enough to cor-
rect the downstream sensor voltage (oxygen content).
The downstream oxygen sensor also provides an
input to determine catalytic convertor efficiency.
Upstream Sensors (California Engines):Tw o
upstream sensors are used (1/1 and 2/1). The 1/1 sen-
sor is the first sensor to receive exhaust gases from
the #1 cylinder. They provide an input voltage to the
PCM. The input tells the PCM the oxygen content of
the exhaust gas. The PCM uses this information to
fine tune fuel delivery to maintain the correct oxygen
content at the downstream oxygen sensors. The PCM
will change the air/fuel ratio until the upstream sen-
sors input a voltage that the PCM has determined
will make the downstream sensors output (oxygen
content) correct.
The upstream oxygen sensors also provide an input
to determine mini-catalyst efficiency. Main catalytic
convertor efficiency is not calculated with this pack-
age.
Downstream Sensors (California Engines):
Two downstream sensors are used (1/2 and 2/2). The
downstream sensors are used to determine the cor-
rect air-fuel ratio. As the oxygen content changes at
the downstream sensor, the PCM calculates how
much air-fuel ratio change is required. The PCM
then looks at the upstream oxygen sensor voltage,
and changes fuel delivery until the upstream sensor
voltage changes enough to correct the downstream
sensor voltage (oxygen content).The downstream oxygen sensors also provide an
input to determine mini-catalyst efficiency. Main cat-
alytic convertor efficiency is not calculated with this
package.
Engines equipped with either a downstream sen-
sor(s), or a post-catalytic sensor, will monitor cata-
lytic convertor efficiency. If efficiency is below
emission standards, the Malfunction Indicator Lamp
(MIL) will be illuminated and a Diagnostic Trouble
Code (DTC) will be set. Refer to Monitored Systems
in Emission Control Systems for additional informa-
tion.
REMOVAL
Never apply any type of grease to the oxygen
sensor electrical connector, or attempt any sol-
dering of the sensor wiring harness.
Oxygen sensor (O2S) locations are shown in (Fig.
33) and (Fig. 34).
WARNING: THE EXHAUST MANIFOLD, EXHAUST
PIPES AND CATALYTIC CONVERTER(S) BECOME
VERY HOT DURING ENGINE OPERATION. ALLOW
ENGINE TO COOL BEFORE REMOVING OXYGEN
SENSOR.
(1) Raise and support vehicle.
(2) Disconnect O2S pigtail harness from main wir-
ing harness.
(3) If equipped, disconnect sensor wire harness
mounting clips from engine or body.
CAUTION: When disconnecting sensor electrical
connector, do not pull directly on wire going into
sensor.
(4) Remove O2S sensor with an oxygen sensor
removal and installation tool.
INSTALLATION
Threads of new oxygen sensors are factory coated
with anti-seize compound to aid in removal.DO
NOT add any additional anti-seize compound to
threads of a new oxygen sensor.
(1) Install O2S sensor. Tighten to 30 N´m (22 ft.
lbs.) torque.
(2) Connect O2S sensor wire connector to main
wiring harness.
(3) If equipped, connect sensor wire harness
mounting clips to engine or body.When Equipped:
The O2S pigtail harness must be clipped and/or
bolted back to their original positions on
engine or body to prevent mechanical damage
to wiring..
(4) Lower vehicle.
WJFUEL INJECTION 14 - 51
O2S SENSOR (Continued)