2003 CHRYSLER CARAVAN width

white letters. To remove the protective coating, apply
warm water and let it soak for a few minutes. After-
wards, scrub the coating away with a soft bristle
brush. Steam cleaning may also be used to remove
the coating.
CAUTION: DO NOT use gasoline, mineral oil, oil-
based solvent or a wire brush for cleaning.
WHEELS
DESCRIPTION - WHEEL
Original equipment wheels are designed for proper
operation at all loads up to the specified maximum
vehicle capacity.
All models use either steel or aluminum drop-cen-
ter wheels. Every wheel has raised sections between
the rim flanges and rim drop well called safety
humps (Fig. 28). Initial inflation of the tires forces
the bead over these raised sections. In case of air
loss, the safety humps hold the tire in position on the
wheel until the vehicle can be brought to a safe stop.
Cast aluminum wheels require special balance
weights to fit on the flange of the rim (Fig. 29).
When wheel alignment is necessary on a vehicle
with cast aluminum wheels, special wheel clamps are
required to avoid damage to the wheel's finish.
The wheel studs and nuts are designed for specific
wheel applications and must be replaced with equiv-
alent parts.
All aluminum wheels have wheel mounting (lug)
nuts with an enlarged nose. This enlarged nose is
necessary to ensure proper retention of the wheels.
DIAGNOSIS AND TESTING - WHEEL
INSPECTION
Inspect wheels for:
²Excessive runout
²Dents, cracks or irregular bends
²Damaged wheel stud (lug) holes
²Air Leaks
NOTE: Do not attempt to repair a wheel by hammer-
ing, heating or welding.
If a wheel is damaged, an original equipment
replacement wheel should be used. When obtaining
replacement wheels, they must be equivalent in load
carrying capacity. The diameter, width, offset, pilot
hole and bolt circle of the wheel should be the same
as the original wheel.
WARNING: FAILURE TO USE EQUIVALENT
REPLACEMENT WHEELS MAY ADVERSELY
AFFECT THE SAFETY AND HANDLING OF THE
VEHICLE.
WARNING: REPLACEMENT WITH USED WHEELS IS
NOT RECOMMENDED. THE SERVICE HISTORY OF
THE WHEEL MAY HAVE INCLUDED SEVERE TREAT-
MENT OR VERY HIGH MILEAGE. THE RIM COULD
FAIL WITHOUT WARNING.
CLEANING - ALUMINUM WHEEL CARE
Chrome plated and painted aluminum wheels
should be cleaned regularly using mild soap and
water to maintain their luster and to prevent corro-
sion.
Fig. 28 Safety Rim
1 - TIRE
2 - WELL
3 - SAFETY HUMPS
4 - FLANGE
Fig. 29 Styled Aluminum Wheel Weight
1 - TIRE
2 - WHEEL
3 - STYLED WHEEL WEIGHT
22 - 18 TIRES/WHEELSRS
TIRES (Continued)
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(1) Cover waxed paper or plastic with adhesive
backed nylon mesh (dry wall tape) larger than the
patch required (Fig. 8).
(2) Tape waxed paper or plastic sheet with mesh to
a surface that has a compatible contour to the repair
area.
(3) Apply a liberal coat of adhesive over the rein-
forcement mesh (Fig. 8). If necessary apply a second
or third coat of adhesive and mesh after firs coat has
cured. The thickness of the patch should be the same
as the repair area.
(4) After patch has cured, peel waxed paper or
plastic from the back of the patch.
(5) If desired, a thin film coat of adhesive can be
applied to the back of the patch to cover mesh for
added strength.
PANEL PATCH INSTALLATION
(1) Make a paper or cardboard pattern the size
and shape of the cutout hole in the panel.
(2) Trim 3 mm (0.125 in.) from edges of pattern so
patch will have a gap between connecting surfaces.
(3) Using the pattern as a guide, cut the patch to
size.
(4) Cut scrap pieces of patch material into 50 mm
(2 in.) squares to use as patch supports to sustain
the patch in the cutout.
(5) Drill 4 mm (0.160 in.) holes 13 mm (0.5 in.) in
from edge of cutout hole (Fig. 7).
(6) Drill 4 mm (0.160 in.) holes 13 mm (0.5 in.)
away from edge of patch across from holes drilled
around cutout.
(7) Drill 3 mm (0.125 in.) holes in the support
squares 13 mm (0.5 in.) from the edge in the center
of one side.
(8) Scuff the backside of the body panel around the
cutout hole with a scuff pad or sandpaper.
(9) Mix enough adhesive to cover one side of all
support squares.
(10) Apply adhesive to cover one side of all support
squares.
(11) Using number 8 sheet metal screws, secure
support squares to back side of body panel with
adhesive sandwiched between the panel and squares
(Fig. 9).
(12) Position patch in cutout against support
squares and adjust patch until the gap is equal along
all sides (Fig. 10).
(13) Drill 3 mm (0.125 in.) holes in the support
squares through the pre-drilled holes in the patch.
(14) Apply a coat of adhesive to the exposed ends
of the support squares (Fig. 11).
Fig. 7 DAMAGED PANEL CUTOUT AND PATCH
1 - CUTOUT
2 - DAMAGED BODY PANEL
3-4MM(0.160 IN.) HOLES
4 - PATCH CUT TO SIZE
Fig. 8 FABRICATED PANEL
1 - STRUCTURAL ADHESIVE
2 - FIBERGLASS CLOTH OR FIBERGLASS MESH TAPE
3 - WIDTH OF V-GROOVE
4 - WAXED PAPER
Fig. 9 SECURE SUPPORT SQUARES TO BODY PANEL
1 - SUPPORT SQUARES
2 - SCREWS
3 - DAMAGED BODY PANEL
23 - 8 BODYRS
BODY (Continued)
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SPECIFICATIONS - HEATER-A/C SYSTEM
ITEM DESCRIPTION NOTES
Vehicle RS - Caravan, Town & Country, Voyager
System R134a with expansion valve(s)
Compressor Nippondenso - 10S20 ND-8 PAG Oil
Freeze±up Control Evaporator temperature sensor Expansion valve mounted - input
to heater-A/C control module
Low PSI Control Pressure transducer Liquid line mounted - input to
Powertrain Control Module (PCM)
- PCM opens compressor clutch
relay < 29.4 psi
High PSI Control Pressure transducer Liquid line mounted - input to
PCM - PCM opens compressor
clutch relay > 450 psi
Pressure relief valve Compressor mounted - opens >
495 psi
Control Head Single zone, dual zone, and three zone
Manual Temperature Control (MTC) - or
Automatic Temperature Control (ATC), (Two
or Three Zone)PCI data bus messaging - ATC
uses two infrared temperature
sensors
Mode Door Electric actuator Control head driven
Blend Air Door Electric actuator
Fresh/Recirc Door Electric actuator
Blower Motor Control head switch Resistor and relay with MTC,
power module and relay with ATC
Cooling Fans Pulse width modulated variable speed PCM control through solid state
fan relay
Clutch
Clutch Control PCM PCM control through compressor
clutch relay
Clutch Coil Draw 2.2 amps @ 12V   0.5amps@ 70É F
Compressor Clutch Air Gap 0.0209- 0.0359
Diagnostics DRBIIITscan tool
RSHEATING & AIR CONDITIONING24-7
HEATING & AIR CONDITIONING (Continued)
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the mounting plate within the evaporator housing is
the power module electronic circuitry and a large
finned, heat sink. The module mounting plate is
secured with two screws to the evaporator housing
and is accessed for service by rolling down the glove
box from the instrument panel.
The power module heat sink will get hot when in
use. Do not touch the heat sink if the blower motor
has been running. The blower power module cannot
be adjusted or repaired and, if faulty or damaged, it
must be replaced.
OPERATION
The blower power module is connected to the vehi-
cle electrical system through a dedicated take out
and connector of the instrument panel wire harness.
A second connector receptacle receives the pigtail
wire connector from the blower motor. The blower
power module allows the microprocessor-based Auto-
matic Temperature Control (ATC) heater-A/C control
module to calculate and provide infinitely variable
blower motor speeds based upon either manual
blower switch input or the ATC programming using a
Pulse Width Modulated (PWM) circuit strategy. The
PWM voltage is applied to a comparator circuit
which compares the PWM signal voltage to the
blower motor feedback voltage. The resulting output
drives the power module circuitry, which adjusts the
voltage output received from the blower motor relay
to change or maintain the desired blower speed. The
blower power module is diagnosed using a DRBIIIt
scan tool. Refer to the appropriate diagnostic infor-
mation.
REMOVAL
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 ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable.
(2) Open the glove box.
(3) Flex both sides of the glove box bin inward
near the top far enough for the rubber glove box stop
bumpers to clear the sides of the glove box opening,
then roll the glove box downward.
(4) Reach through the glove box opening to access
and disconnect the instrument panel wire harness
connector for the power module from the module con-
nector receptacle.
(5) Reach through the glove box opening to access
and disconnect the blower motor pigtail wire connec-
tor from the power module connector receptacle.
(6) Remove the two screws that secure the power
module to the evaporator housing.
(7) Remove the power module from the evaporator
housing.
INSTALLATION
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 ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Position the power module into the evaporator
housing.
Fig. 22 Power Module
1 - POWER MODULE
2 - LOWER GLOVE BOX OPENING REINFORCEMENT
3 - EVAPORATOR HOUSING
24 - 26 CONTROLS - FRONTRS
POWER MODULE (Continued)
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(7) Install and tighten the screw that secures the
back of the rear heater-A/C unit housing to the right
D-pillar. Tighten the screw to 11 N´m (97 in. lbs.).
(8) Install and tighten the two screws that secure
the top of the quarter trim panel attaching bracket to
the quarter inner panel. Tighten the screws to 1.7
N´m (15 in. lbs.).
(9) Reinstall the right quarter trim panel and
right D-pillar trim panel onto the quarter inner
panel. (Refer to 23 - BODY/INTERIOR/QUARTER
TRIM PANEL - INSTALLATION).
(10) Reconnect the battery negative cable.
(11) Perform the heater-A/C control calibration
procedure. (Refer to 24 - HEATING & AIR CONDI-
TIONING/CONTROLS - FRONT/A/C-HEATER CON-
TROL - STANDARD PROCEDURE - HEATER-A/C
CONTROL CALIBRATION).
POWER MODULE
DESCRIPTION
A blower power module is used on this model when
it is equipped with the optional Automatic Tempera-
ture Control (ATC) (Fig. 11). Models equipped with
the standard manual heater-A/C control use a blower
motor resistor, instead of the blower power module.The blower power module is installed in a mounting
hole in the back of the rear heater-A/C unit housing,
directly above the expansion valve. The module con-
sists of a molded plastic mounting plate with two
integral connector receptacles. Concealed behind the
mounting plate within the evaporator housing is the
power module electronic circuitry and a large finned,
heat sink. The module mounting plate is secured
with two screws to the rear heater-A/C unit housing
and is accessed for service by removing the right
quarter and D-pillar trim panels.
The power module heat sink will get hot when in
use. Do not touch the heat sink if the blower motor
has been running. The blower power module cannot
be adjusted or repaired and, if faulty or damaged, it
must be replaced.
OPERATION
The blower power module is connected to the vehi-
cle electrical system through a dedicated take out
and connector of the rear HVAC wire harness. A sec-
ond connector receptacle receives the pigtail wire
connector from the blower motor. The blower power
module allows the microprocessor-based Automatic
Temperature Control (ATC) heater-A/C control mod-
ule to calculate and provide infinitely variable blower
motor speeds based upon either manual blower
switch input or the ATC programming using a Pulse
Width Modulated (PWM) circuit strategy. The PWM
voltage is applied to a comparator circuit which com-
pares the PWM signal voltage to the blower motor
feedback voltage. The resulting output drives the
power module circuitry, which adjusts the voltage
output received from the blower motor relay to
change or maintain the desired blower speed. The
blower power module is diagnosed using a DRBIIIt
scan tool. Refer to the appropriate diagnostic infor-
mation.
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the right quarter trim panel and right
D-pillar trim panel from the quarter inner panel.
(Refer to 23 - BODY/INTERIOR/QUARTER TRIM
PANEL - REMOVAL).
(3) Disconnect the rear HVAC wire harness con-
nector for the blower power module from the resistor
connector receptacle (Fig. 12).
(4) Disconnect the blower motor pigtail wire con-
nector from the blower power module connector
receptacle.
(5) Remove the two screws that secure the blower
power module to the rear heater-A/C unit housing.
(6) Remove the blower power module from the rear
heater-A/C unit housing.
Fig. 11 Power Module
1 - REAR HEATER-A/C UNIT HOUSING
2 - SCREW (2)
3 - D-PILLAR
4 - BLOWER PIGTAIL WIRE
5 - REAR HVAC WIRE HARNESS
6 - EXPANSION VALVE
7 - BLOWER POWER MODULE
RSCONTROLS - REAR24-37
MODE DOOR ACTUATOR (Continued)
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BLOWER MOTOR
DESCRIPTION
The blower motor is a 12-volt, Direct Current (DC)
motor with a squirrel cage-type blower wheel that is
secured to the blower motor shaft (Fig. 7). The
blower motor and wheel are located near the passen-
ger side end of the heater-A/C unit within the two
halves of the intake air housing in the passenger
compartment below the instrument panel. The
blower motor and blower motor wheel are a factory
balanced unit and cannot be adjusted or repaired. If
faulty or damaged, the blower motor and blower
wheel must be replaced as a unit.
OPERATION
The blower motor will operate whenever the igni-
tion switch is in the On position and the heater-A/C
control power is turned on. The blower motor can
only be turned off by turning off the power at the
heater-A/C control. The blower motor receives battery
current whenever the front blower motor relay is
energized. The front blower motor relay output cir-
cuit is protected by a fuse in the Intelligent Power
Module (IPM) located in the engine compartment
near the battery. In the Manual system, the blower
motor speed is controlled by regulating the path to
ground through the blower control switch and the
blower motor resistor. In the ATC system, the blower
motor speed is controlled by an electronic blower
power module, which uses a pulse width modulated
input from the ATC module and feedback from the
blower motor to regulate the blower motor ground
path it provides. The blower motor and wheel areused to control the velocity of air moving through the
heater-A/C unit housing. The blower motor controls
the velocity of the air flowing through the heater-A/C
housing by spinning the blower wheel within the
housing at the selected speed or, in the ATC system,
at the selected or programmed speed.
DIAGNOSIS AND TESTING - BLOWER MOTOR
BLOWER MOTOR INOPERATIVE
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 ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Check the fuse (Fuse 10 - 40 ampere) in the
Intelligent Power Module (IPM). If OK, go to Step 2.
If not OK, repair the shorted circuit or component as
required and replace the faulty fuse.
(2) Turn the ignition switch to the On position. Be
certain that the heater-A/C control power is turned
on. Check for battery voltage at the fuse (Fuse 10 -
40 ampere) in the IPM. If OK, go to Step 3. If not
OK, proceed to diagnosis of the front blower motor
relay. (Refer to 24 - HEATING & AIR CONDITION-
ING/CONTROLS - FRONT/BLOWER MOTOR
RELAY - DIAGNOSIS AND TESTING).
(3) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the front HVAC wire harness connector
for the front blower motor resistor (Manual Temper-
ature Control) or the front blower power module
(Automatic Temperature Control) from the resistor or
module connector receptacle. Reconnect the battery
negative cable. Turn the ignition switch to the On
position. Be certain that the heater-A/C control
power is turned on. Check for battery voltage at the
fused front blower motor relay output circuit cavity
of the front HVAC wire harness connector for the
front blower motor resistor (MTC) or the front blower
power module (ATC). If OK, go to Step 4. If not OK,
repair the open fused front blower motor relay output
circuit to the IPM as required.
Fig. 7 Blower Motor
1 - BLOWER MOTOR
2 - RUBBER GROMMET
3 - BLOWER MOTOR CONNECTOR
4 - MOUNTING TABS
RSDISTRIBUTION - FRONT24-43
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OPERATION
The rear blower motor will operate whenever the
ignition switch is in the On position, the heater-A/C
control power is turned on, and the rear heater-A/C
system control switch on the front heater-A/C control
is not in the Off position. The blower motor can only
be turned off by turning off the rear system at the
front heater-A/C control. The blower motor receives
battery current whenever the rear blower motor
relay is energized. The rear blower motor relay out-
put circuit is protected by a fuse in the Intelligent
Power Module (IPM) located in the engine compart-
ment near the battery. In the MTC system, the
blower motor speed is controlled by regulating the
path to ground through the blower control switch and
the blower motor resistor. In the ATC system, the
blower motor speed is controlled by an electronic
blower power module, which uses a pulse width mod-
ulated input from the ATC module and feedback from
the blower motor to regulate the blower motor
ground path it provides. The blower motor and wheel
are used to control the velocity of air moving through
the rear heater-A/C unit housing. The blower motor
controls the velocity of the air flowing through the
rear heater-A/C housing by spinning the blower
wheel within the housing at the selected speed or, in
the ATC system, at the selected or programmed
speed.
DIAGNOSIS AND TESTING - BLOWER MOTOR
BLOWER MOTOR INOPERATIVE
(1) Check the fuse (Fuse 12 - 25 ampere) in the
Intelligent Power Module (IPM). If OK, go to Step 2.
If not OK, repair the shorted circuit or component as
required and replace the faulty fuse.
(2) Turn the ignition switch to the On position. Be
certain that the rear heater-A/C control power is
turned on. Check for battery voltage at the fuse
(Fuse 12 - 25 ampere) in the IPM. If OK, go to Step
3. If not OK, proceed to diagnosis of the rear blower
motor relay. (Refer to 24 - HEATING & AIR CONDI-
TIONING/CONTROLS - REAR/BLOWER MOTOR
RELAY - DIAGNOSIS AND TESTING).(3) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the rear HVAC wire harness connector for
the rear blower motor resistor (Manual Temperature
Control) or the rear blower power module (Automatic
Temperature Control) from the resistor or module
connector receptacle. Reconnect the battery negative
cable. Turn the ignition switch to the On position. Be
certain that the rear heater-A/C control power is
turned on. Check for battery voltage at the fused
rear blower motor relay output circuit cavity of the
rear HVAC wire harness connector for the rear
blower motor resistor (MTC) or the rear blower
power module (ATC). If OK, go to Step 4. If not OK,
repair the open fused front blower motor relay output
circuit to the IPM as required.
(4) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the rear blower motor pigtail wire connec-
tor from the take out and connector of the rear
HVAC wire harness (MTC) or the connector recepta-
cle of the rear blower power module (ATC). Use
jumper wires to connect a battery and ground feeds
to the blower motor pigtail wire connector. The
blower motor should operate. If OK with MTC, pro-
ceed to diagnosis of the rear blower motor resistor.
(Refer to 24 - HEATING & AIR CONDITIONING/
CONTROLS - REAR/BLOWER MOTOR RESISTOR -
DIAGNOSIS AND TESTING). If OK with ATC, use a
DRBIII scan tool to diagnose the rear blower power
module. Refer to the appropriate diagnostic informa-
tion. If not OK with MTC or ATC, replace the faulty
rear blower motor.
BLOWER MOTOR NOISE OR VIBRATION
Refer to the Blower Motor Noise/Vibration Diagno-
sis chart (Fig. 4).
24 - 54 DISTRIBUTION - REARRS
BLOWER MOTOR (Continued)
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The following is a list of the monitored compo-
nents:
²Comprehensive Components
²Oxygen Sensor Monitor
²Oxygen Sensor Heater Monitor
²Catalyst Monitor
COMPREHENSIVE COMPONENTS
Along with the major monitors, OBD II requires
that the diagnostic system monitor any component
that could affect emissions levels. In many cases,
these components were being tested under OBD I.
The OBD I requirements focused mainly on testing
emissions-related components for electrical opens and
shorts.
However, OBD II also requires that inputs from
powertrain components to the PCM be tested for
rationality, and that outputs to powertrain compo-
nents from the PCM be tested forfunctionality.
Methods for monitoring the various Comprehensive
Component monitoring include:
(1) Circuit Continuity
²Open
²Shorted high
²Shorted to ground
(2) Rationality or Proper Functioning
²Inputs tested for rationality
²Outputs tested for functionality
NOTE: Comprehensive component monitors are
continuous. Therefore, enabling conditions do not
apply.
Input RationalityÐWhile input signals to the
PCM are constantly being monitored for electrical
opens and shorts, they are also tested for rationality.
This means that the input signal is compared against
other inputs and information to see if it makes sense
under the current conditions.
PCM sensor inputs that are checked for rationality
include:
²Manifold Absolute Pressure (MAP) Sensor
²Oxygen Sensor (O2S)
²Engine Coolant Temperature (ECT) Sensor
²Camshaft Position (CMP) Sensor
²Vehicle Speed Sensor
²Crankshaft Position (CKP) Sensor
²Intake/inlet Air Temperature (IAT) Sensor
²Throttle Position (TPS) Sensor
²Ambient Temperature Sensors
²Power Steering Switch
²Oxygen Sensor Heater
²Brake Switch
²Leak Detection Pump Switch or NVLD switch (if
equipped)
²P/N SwitchOutput FunctionalityÐPCM outputs are tested
for functionality in addition to testing for opens and
shorts. When the PCM provides a voltage to an out-
put component, it can verify that the command was
carried out by monitoring specific input signals for
expected changes. For example, when the PCM com-
mands the Idle Air Control (IAC) Motor to a specific
position under certain operating conditions, it expects
to see a specific (target) idle speed (RPM). If it does
not, it stores a DTC.
PCM outputs monitored for functionality include:
²Fuel Injectors
²Ignition Coils
²Idle Air Control
²Purge Solenoid
²EGR Solenoid (if equipped)
²LDP Solenoid or NVLD solenoid (if equipped)
²Radiator Fan Control
²Trans Controls
OXYGEN SENSOR (O2S) MONITOR
DESCRIPTIONÐEffective control of exhaust
emissions is achieved by an oxygen feedback system.
The most important element of the feedback system
is the O2S. The O2S is located in the exhaust path.
Once it reaches operating temperature 300É to 350ÉC
(572É to 662ÉF), the sensor generates a voltage that
is inversely proportional to the amount of oxygen in
the exhaust. When there is a large amount of oxygen
in the exhaust caused by a lean condition, the sensor
produces a low voltage, below 450 mV. When the oxy-
gen content is lower, caused by a rich condition, the
sensor produces a higher voltage, above 450mV (volt-
ages are offset by 2.5 volts on NGC vehicles).
The information obtained by the sensor is used to
calculate the fuel injector pulse width. The PCM is
programmed to maintain the optimum air/fuel ratio.
At this mixture ratio, the catalyst works best to
remove hydrocarbons (HC), carbon monoxide (CO)
and nitrous oxide (NOx) from the exhaust.
The O2S is also the main sensing element for the
EGR (if equipped), Catalyst and Fuel Monitors.
The O2S may fail in any or all of the following
manners:
²Slow response rate (Big Slope)
²Reduced output voltage (Half Cycle)
²Heater Performance
Slow Response Rate (Big Slope)ÐResponse rate
is the time required for the sensor to switch from
lean to rich signal output once it is exposed to a
richer than optimum A/F mixture or vice versa. As
the PCM adjusts the air/fuel ratio, the sensor must
be able to rapidly detect the change. As the sensor
ages, it could take longer to detect the changes in the
oxygen content of the exhaust gas. The rate of
change that an oxygen sensor experiences is called
25 - 2 EMISSIONS CONTROLRS
EMISSIONS CONTROL (Continued)
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