volt CHRYSLER VOYAGER 2004 Service Manual

OPERATION
The rear mode door actuator is connected to the
front heater-A/C control module through the vehicle
electrical system by a dedicated two-wire take out
and connector of the rear HVAC wire harness. The
rear mode door actuator can move the mode door in
two directions. When the front heater-A/C control
module pulls the voltage on one side of the motor
connection high and the other connection low, the
rear mode door will move in one direction. When the
module reverses the polarity of the voltage to the
motor, the rear mode door moves in the opposite
direction. When the module makes the voltage to
both connections high or both connections low, the
mode door stops and will not move. These same
motor connections also provide a feedback signal to
the front heater-A/C control module. This feedback
signal allows the module to monitor the operation
and relative positions of the rear mode door actuator
and the mode door. The front heater-A/C control mod-
ule learns the rear mode door stop positions during
the calibration procedure and will store a Diagnostic
Trouble Code (DTC) for any problems it detects in
the mode door actuator circuits.
The rear mode door actuator can be diagnosed
using a DRBIIItscan tool. Refer to Body Diagnostic
Procedures for more information. The rear mode door
actuator cannot be adjusted or repaired and, if dam-
aged or faulty, it must be replaced.
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) Remove the two screws that secure the top of
the quarter trim panel attaching bracket to the quar-
ter inner panel.
(4) Remove the screw that secures the back of the
rear HVAC housing to the right D-pillar.
(5) Remove the screw that secures the front of the
rear HVAC housing to the right quarter inner panel.
(6) Carefully pull the top of the rear HVAC hous-
ing away from the right quarter inner panel far
enough to reach between the rear HVAC housing and
the quarter inner panel to access the rear mode door
actuator (Fig. 7).
(7) Remove the two screws that secure the mode
door actuator to the rear HVAC housing.
(8) Pull the mode door actuator away from the
rear HVAC housing far enough to disengage the
actuator output shaft from the mode door linkage.(9) Raise the mode door actuator far enough to
access and disconnect the rear HVAC wire harness
connector from the actuator
(10) Remove the rear mode door actuator from
between the rear HVAC housing and the quarter
inner panel.
INSTALLATION
(1) Position the mode door actuator between the
rear HVAC housing and the quarter inner panel.
(2) Reconnect the rear HVAC wire harness connec-
tor to the rear mode door actuator.
(3) Position the rear mode door actuator onto the
rear HVAC housing. If necessary, rotate the actuator
slightly to align the splines on the actuator output
shaft with those in the mode door linkage.
(4) Install the two screws that secure the rear
mode door actuator to the rear HVAC housing.
Tighten the screws to 2 N´m (17 in. lbs.).
(5) Push the top of the rear HVAC housing back
into position against the right quarter inner panel.
Fig. 7 Rear HVAC Blend Door Actuator
1 - SCREW (2)
2 - MODE DOOR ACTUATOR
3 - SCREW (2)
4 - CONNECTOR
5 - BLEND DOOR ACTUATOR
6 - WIRE HARNESS CONNECTOR
24 - 40 CONTROLS - REARRS
MODE DOOR ACTUATOR - REAR (Continued)

(6) Install the screw that secures the front of the
rear HVAC housing to the right quarter inner panel.
Tighten the screw to 11 N´m (97 in. lbs.).
(7) Install the screw that secures the back of the
rear HVAC housing to the right D-pillar. Tighten the
screw to 11 N´m (97 in. lbs.).
(8) Install the two screws that secure the top of
the quarter trim panel attaching bracket to the quar-
ter inner panel. Tighten the screws to 2 N´m (17 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 - REAR
BLOWER MOTOR
DESCRIPTION
A rear blower motor power module is used on this
model when it is equipped with the optional Auto-
matic Temperature Control (ATC) system. Models
equipped with the standard manual heater-A/C sys-
tem use a blower motor resistor block , instead of the
blower motor power module (Refer to 24 - HEATING
& AIR CONDITIONING/CONTROLS/BLOWER
MOTOR RESISTOR BLOCK - DESCRIPTION).
The rear blower motor power module is installed in
the back of the rear HVAC housing, directly above
the expansion valve. The module consists 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
power module is accessed for service by removing the
right quarter and D-pillar trim panels.
OPERATION
The rear blower motor power module is connected
to the vehicle electrical system through a dedicated
take out and connector of the rear HVAC wire har-
ness. A second connector receptacle receives the pig-
tail wire connector from the rear blower motor. The
rear blower motor power module allows the micropro-
cessor-based Automatic 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 pro-
gramming 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
rear blower motor relay to change or maintain the
desired blower speed. The rear blower motor power
module is diagnosed using a DRBIIItscan tool. Refer
to Body Diagnostic Procedures.
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 from the rear blower motor power module
(Fig. 8).
(4) Disconnect the rear blower motor pigtail wire
connector from the rear blower motor power module.
(5) Remove the two screws that secure the rear
blower motor power module to the rear HVAC hous-
ing.
(6) Remove the rear blower motor power module
from the rear HVAC housing.
Fig. 8 Rear Blower Motor Power Module
1 - REAR HVAC HOUSING
2 - SCREW (2)
3 - D-PILLAR
4 - REAR BLOWER MOTOR PIGTAIL WIRE
5 - REAR HVAC WIRE HARNESS
6 - EXPANSION VALVE
7 - REAR BLOWER MOTOR POWER MODULE
RSCONTROLS - REAR24-41
MODE DOOR ACTUATOR - REAR (Continued)

(2) Engage the retainer features on the top of the
outlet housing with their receptacles at the top of the
center bezel, then roll the bottom of the outlet hous-
ing downwards towards the center bezel.
(3) Install the three screws that secure the bottom
of the outlet housing to the center bezel. Tighten the
screws to 2 N´m (17 in. lbs.).
(4) If the vehicle is equipped with the optional
ATC system, reconnect the ATC remote infrared tem-
perature sensor jumper harness to the sensor connec-
tor receptacle located on the bottom of the center
outlet housing.
(5) Reinstall the center bezel onto the instrument
panel (Refer to 23 - BODY/INSTRUMENT PANEL/
INSTRUMENT PANEL CENTER BEZEL - INSTAL-
LATION).
(6) Reconnect the battery negative cable.
INSTALLATION - DEMISTER OUTLET
(1) Position the demister outlet over the demister
duct opening in the instrument panel top pad.
(2) Using hand pressure, press the demister outlet
firmly and evenly into the instrument panel top pad
opening until the snap features on the outlet are
fully engaged.
INSTALLATION - INSTRUMENT PANEL OUTLET
(1) Position the instrument panel outlet into the
panel duct opening in the instrument panel top pad.
(2) Using hand pressure, press the instrument
panel outlet firmly and evenly into the instrument
panel top pad opening until the snap features on the
outlet are fully engaged.
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. 6). The
blower motor and wheel are located near the passen-
ger side end of the HVAC housing in the passenger
compartment below the instrument panel. The
blower motor and blower motor wheel are factory bal-
anced and cannot be adjusted or repaired. If faulty or
damaged, the blower motor and blower wheel must
be replaced as an assembly.
OPERATION
On models equipped with the manual heater-A/C
system, the blower motor will operate whenever the
ignition switch is in the On position and the blower
control switch is in any position except Off. On mod-
els equipped with the Automatic Temperature Con-
trol (ATC) system, the blower motor will operate
whenever the ignition switch is in the On position
and the A/C-heater control power is turned on.
The blower motor receives battery current when-
ever the front blower motor relay is energized. The
front blower motor relay output circuit is protected
by a fuse in the Integrated Power Module (IPM)
located in the engine compartment near the battery.
In the manual heater-A/C 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 motor
power module, which uses a pulse width modulated
input from the ATC module and feedback from the
Fig. 5 Instrument Panel Outlet - Left Side Shown
1 - INSTRUMENT PANEL TOP PAD
2 - INSTRUMENT PANEL OUTLET
3 - TRIM STICK
Fig. 6 Blower Motor
1 - BLOWER MOTOR
2 - RUBBER GROMMET
3 - BLOWER MOTOR CONNECTOR
4 - MOUNTING TABS
24 - 46 DISTRIBUTION - FRONTRS
AIR OUTLETS (Continued)

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
HVAC housing by spinning the blower wheel within
the housing at the selected speed or, in the ATC sys-
tem, 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.
For circuit descriptions and diagrams, refer to the
appropriate wiring information. The wiring informa-
tion includes wiring, diagrams, proper wire and con-
nector repair procedures, further details on wire
harness routing and retention, as well as pin-out and
location views for the various wire harness connec-
tors, splices and grounds.
BLOWER MOTOR ELECTRICAL DIAGNOSIS
(1) Check the fuse (Fuse 10 - 40 ampere) in the
Integrated 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 A/C-heater 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, check the front blower motor relay.
(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 block (Manual
Temperature Control) or the front blower motor
power module (Automatic Temperature Control) from
the resistor or module connector receptacle. Recon-
nect the battery negative cable. Turn the ignition
switch to the On position. Be certain that the A/C-
heater 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 connec-
tor for the front blower motor resistor block (MTC) orthe front blower motor 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 front blower motor pigtail wire con-
nector from the connector receptacle of the front
blower motor resistor block (MTC) or the front
blower motor 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, proceed to diagno-
sis of the front blower motor resistor block (Refer to
24 - HEATING & AIR CONDITIONING/CONTROLS
- FRONT/BLOWER MOTOR RESISTOR - DIAGNO-
SIS AND TESTING). If OK with ATC, use a DRBIII
scan tool to diagnose the front blower motor power
module. Refer to Body Diagnostic information. If not
OK with MTC or ATC, replace the faulty front blower
motor.
BLOWER MOTOR NOISE OR VIBRATION
Refer to the Blower Motor Noise/Vibration Diagno-
sis chart for basic checks of the blower motor when a
vibration or noise is present (Fig. 7).
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 AN ACCIDENTAL
AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
NOTE: The blower motor is located on the passen-
ger side of the vehicle under the instrument panel.
The blower motor can be removed from the vehicle
without having to remove the HVAC housing.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the passenger side door sill plate and
cowl panel.
(3) Pull back the carpet to access the front lower
air intake screw.
RSDISTRIBUTION - FRONT24-47
BLOWER MOTOR (Continued)

DISTRIBUTION DUCT
REMOVAL
(1) Remove the trim from the right quarter inner
panel and the right D pillaR (Refer to 23 - BODY/IN-
TERIOR/RIGHT QUARTER TRIM PANEL -
REMOVAL).
(2) Slide the rear distribution duct upwards far
enough to disengage it from the outlet at the top of
the rear HVAC housing (Fig. 2).
(3) While pulling the lower end of the rear distri-
bution duct away from the rear HVAC housing out-
let, disengage the upper end of the distribution duct
from the headliner duct.
(4) Remove the rea distribution duct from the
vehicle.
INSTALLATION
(1) Align the upper end of the rear distribution
duct to the headliner duct.
(2) Slide the upper end of the rear distribution
duct onto the headliner duct far enough to align the
lower end of the duct with the outlet at the top of the
rear HVAC housing.
(3) Slide the rear distribution duct downwards far
enough to engage it onto the outlet at the top of the
rear HVAC housing.
(4) Reinstall the trim onto the right quarter inner
panel and the right D pillar (Refer to 23 - BODY/IN-
TERIOR/RIGHT QUARTER TRIM PANEL -
INSTALLATION).
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. The blower motor
and wheel are located near the top of the rear HVAC
housing in the passenger compartment behind the
right rear wheel house. The rear HVAC housing must
be removed from the vehicle to access the blower
motor for service. 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
On models equipped with the Manual Temperature
Control (MTC) system, the rear blower motor will
operate only whenever the ignition switch is in the
On position, the front blower control switch is in any
position except Off and the rear blower control switch
on the front A/C-heater control is in any position
except Off. On models equipped with the Automatic
Temperature Control (ATC) system, the blower motor
will operate whenever the ignition switch is in the
On position, the A/C-heater control power is turned
on and the rear blower control switch on the front
A/C-heater control is in any position except Off. The
rear blower motor can only be turned off by turning
off the rear system at the front A/C-heater control.
The rear blower motor receives battery current
whenever the rear blower motor relay is energized.
The rear blower motor relay output circuit is pro-
tected by a fuse in the Integrated Power Module
(IPM) located in the engine compartment near the
battery. In the MTC system, the rear 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 rear blower
motor speed is controlled by an electronic blower
motor power module, which uses a pulse width mod-
ulated input from the ATC control module and feed-
back from the rear blower motor to regulate the
blower motor ground path it provides. The rear
blower motor and wheel are used to control the veloc-
ity of air moving through the rear HVAC housing.
The rear blower motor controls the velocity of the air
flowing through the rear HVAC housing by spinning
the blower wheel within the housing at the selected
speed or, in the ATC system, at the selected or pro-
grammed speed.
Fig. 2 Rear Distribution Duct
1 - HEADLINER DUCT
2 - REAR DISTRIBUTION DUCT
3 - REAR HVAC HOUSING OUTLET
RSDISTRIBUTION - REAR24-57

DIAGNOSIS AND TESTING - REAR BLOWER
MOTOR
BLOWER MOTOR INOPERATIVE
For circuit descriptions and diagrams, refer to the
appropriate wiring information. The wiring informa-
tion includes wiring, diagrams, proper wire and con-
nector repair procedures, further details on wire
harness routing and retention, as well as pin-out and
location views for the various wire harness connec-
tors, splices and grounds.
BLOWER MOTOR ELECTRICAL DIAGNOSIS
(1) Check the fuse (Fuse 12 - 25 ampere) in the
Integrated 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 A/C-heater 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, check the rear blower motor relay.
(3) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the rear HVAC wire harness connector
from the rear blower motor resistor block (Manual
Temperature Control) or the rear blower motor power
module (Automatic Temperature Control). Reconnect
the battery negative cable. Turn the ignition switch
to the On position. Be certain that the rear A/C-
heater 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 connec-
tor for the rear blower motor resistor block (MTC) or
the rear blower motor 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 rear HVAC wire harness (MTC) or the
rear blower power module (ATC). Use jumper wires
to connect a battery and ground feeds to the blower
motor pigtail wire connector. The rear blower motor
should operate. If OK with MTC, proceed to diagno-
sis of the rear blower motor resistor block (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 motor power module.
Refer to the appropriate diagnostic information. 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 for basic checks of the blower motor when a
vibration or noise is present (Fig. 3).
REMOVAL
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMBING -
WARNING) and (Refer to 24 - HEATING & AIR CON-
DITIONING/PLUMBING - CAUTION).
(1) Remove the rear HVAC housing from the vehi-
cle (Refer to 24 - HEATING & AIR CONDITIONING/
DISTRIBUTION/HVAC HOUSING - REMOVAL).
(2) Disconnect the rear blower motor pigtail wire
connector.
NOTE: With the Manual Temperature Control sys-
tem, the blower motor pigtail wire is connected to a
take out and connector of the rear HVAC wire har-
ness. With the Automatic Temperature Control sys-
tem , the blower pigtail wire is connected to a
receptacle on the blower motor power module.
(3) Remove the three screws that secure the rear
blower motor to the outboard side of the rear HVAC
housing (Fig. 4).
(4) Remove the rear blower motor from the rear
HVAC housing.
INSTALLATION
(1) Position the rear blower motor into the rear
HVAC housing.
(2) Install the three screws that secure the blower
motor to the rear HVAC housing. Tighten the screws
to 2 N´m (17 in. lbs.).
(3) Reconnect the rear blower motor pigtail wire
connector.
NOTE: With the Manual Temperature Control system
, the blower pigtail wire is connected to a take out
and connector of the rear HVAC wire harness. With
the Automatic Temperature Control system, the
blower pigtail wire is connected to a receptacle on
the blower motor power module.
24 - 58 DISTRIBUTION - REARRS
BLOWER MOTOR (Continued)

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)

ªBig Slopeº. The PCM checks the oxygen sensor volt-
age in increments of a few milliseconds.
Reduced Output Voltage (Half Cycle)ÐThe
output voltage of the O2S ranges from 0 to 1 volt
(voltages are offset by 2.5 volts on NGC vehicles). A
good sensor can easily generate any output voltage in
this range as it is exposed to different concentrations
of oxygen. To detect a shift in the A/F mixture (lean
or rich), the output voltage has to change beyond a
threshold value. A malfunctioning sensor could have
difficulty changing beyond the threshold value. Each
time the voltage signal surpasses the threshold, a
counter is incremented by one. This is called the Half
Cycle Counter.
Heater PerformanceÐThe heater is tested by a
separate monitor. Refer to the Oxygen Sensor Heater
Monitor.
OPERATIONÐAs the Oxygen Sensor signal
switches, the PCM monitors the half cycle and big
slope signals from the oxygen sensor. If during the
test neither counter reaches a predetermined value, a
malfunction is entered and Freeze Frame data is
stored. Only one counter reaching its predetermined
value is needed for the monitor to pass.
The Oxygen Sensor Monitor is a two trip monitor
that is tested only once per trip. When the Oxygen
Sensor fails the test in two consecutive trips, the
MIL is illuminated and a DTC is set. The MIL is
extinguished when the Oxygen Sensor monitor
passes in three consecutive trips. The DTC is erased
from memory after 40 consecutive warm-up cycles
without test failure.
Enabling ConditionsÐThe following conditions
must typically be met for the PCM to run the oxygen
sensor monitor:
²Battery voltage
²Engine temperature
²Engine run time
²Engine run time at a predetermined speed
²Engine run time at a predetermined speed and
throttle opening
²Transmission in gear and brake depressed (auto-
matic only)
²Fuel system in Closed Loop
²Long Term Adaptive (within parameters)
²Power Steering Switch in low PSI (no load)
²Engine at idle
²Fuel level above 15%
²Ambient air temperature
²Barometric pressure
²Engine RPM within acceptable range of desired
idle
Pending ConditionsÐThe Task Manager typi-
cally does not run the Oxygen Sensor Monitor if over-
lapping monitors are running or the MIL is
illuminated for any of the following:²Misfire Monitor
²Front Oxygen Sensor and Heater Monitor
²MAP Sensor
²Vehicle Speed Sensor
²Engine Coolant Temperature Sensor
²Throttle Position Sensor
²Engine Controller Self Test Faults
²Cam or Crank Sensor
²Injector and Coil
²Idle Air Control Motor
²EVAP Electrical
²EGR Solenoid Electrical (if equipped)
²Intake/inlet Air Temperature
²5 Volt Feed
ConflictÐThe Task Manager does not run the
Oxygen Sensor Monitor if any of the following condi-
tions are present:
²A/C ON (A/C clutch cycling temporarily sus-
pends monitor)
²Purge flow in progress
²Ethanol content learn is taking place and the
ethanol used once flag is set (if equipped)
SuspendÐThe Task Manager suspends maturing
a fault for the Oxygen Sensor Monitor if any of the
following are present:
²Oxygen Sensor Heater Monitor, Priority 1
²Misfire Monitor, Priority 2
OXYGEN SENSOR HEATER MONITOR
DESCRIPTIONÐIf there is an oxygen sensor
(O2S) DTC as well as a O2S heater DTC, the O2S
fault MUST be repaired first. After the O2S fault is
repaired, verify that the heater circuit is operating
correctly.
The voltage readings taken from the O2S are very
temperature sensitive. The readings are not accurate
below a sensor temperature of 300ÉC. Heating of the
O2S is done to allow the engine controller to shift to
closed loop control as soon as possible. The heating
element used to heat the O2S must be tested to
ensure that it is heating the sensor properly.
The heater element itself is not tested. The sensor
output is used to test the heater by isolating the
effect of the heater element on the O2S output volt-
age from the other effects. The resistance is normally
between 100 ohms and 4.5 megaohms. When oxygen
sensor temperature increases, the resistance in the
internal circuit decreases. The PCM sends a 5 volts
biased signal through the oxygen sensors to ground
this monitoring circuit. As the temperature increases,
resistance decreases and the PCM detects a lower
voltage at the reference signal. Inversely, as the tem-
perature decreases, the resistance increases and the
PCM detects a higher voltage at the reference signal.
The O2S circuit is monitored for a drop in voltage.
RSEMISSIONS CONTROL25-3
EMISSIONS CONTROL (Continued)

OPERATIONÐThe Oxygen Sensor Heater Moni-
tor begins after the ignition has been turned OFF.
The PCM sends a 5 volt bias to the oxygen sensor
every 1.6 seconds. The PCM keeps it biased for 35
ms each time. As the sensor cools down, the resis-
tance increases and the PCM reads the increase in
voltage. Once voltage has increased to a predeter-
mined amount, higher than when the test started,
the oxygen sensor is cool enough to test heater oper-
ation.
When the oxygen sensor is cool enough, the PCM
energizes the ASD relay. Voltage to the O2 sensor
begins to increase the temperature. As the sensor
temperature increases, the internal resistance
decreases. The PCM continues biasing the 5 volt sig-
nal to the sensor. Each time the signal is biased, the
PCM reads a voltage decrease. When the PCM
detects a voltage decrease of a predetermined value
for several biased pulses, the test passes.
The heater elements are tested each time the
engine is turned OFF if all the enabling conditions
are met. If the monitor fails, the PCM stores a
maturing fault and a Freeze Frame is entered. If two
consecutive tests fail, a DTC is stored. Because the
ignition is OFF, the MIL is illuminated at the begin-
ning of the next key cycle.
Enabling ConditionsÐThe following conditions
must be met for the PCM to run the oxygen sensor
heater test:
²Engine run time of at least 3 minutes
²Engine run time at a predetermined speed
and throttle opening.
²Key OFF power down
²Battery voltage of at least 10 volts
²Sufficient Oxygen Sensor cool down
Pending ConditionsÐThere are not conditions or
situations that prompt conflict or suspension of test-
ing. The oxygen sensor heater test is not run pending
resolution of MIL illumination due to oxygen sensor
failure.
SuspendÐThere are no conditions which exist for
suspending the Heater Monitor.
CATALYST MONITOR
To comply with clean air regulations, vehicles are
equipped with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide.
Normal vehicle miles or engine misfire can cause a
catalyst to decay. A meltdown of the ceramic core can
cause a reduction of the exhaust passage. This can
increase vehicle emissions and deteriorate engine
performance, driveability and fuel economy.
The catalyst monitor uses dual oxygen sensors
(O2S's) to monitor the efficiency of the converter. The
dual O2S strategy is based on the fact that as a cat-alyst deteriorates, its oxygen storage capacity and its
efficiency are both reduced. By monitoring the oxy-
gen storage capacity of a catalyst, its efficiency can
be indirectly calculated. The upstream O2S is used to
detect the amount of oxygen in the exhaust gas
before the gas enters the catalytic converter. The
PCM calculates the A/F mixture from the output of
the O2S. A low voltage indicates high oxygen content
(lean mixture). A high voltage indicates a low content
of oxygen (rich mixture).
When the upstream O2S detects a lean condition,
there is an abundance of oxygen in the exhaust gas.
A functioning converter would store this oxygen so it
can use it for the oxidation of HC and CO. As the
converter absorbs the oxygen, there will be a lack of
oxygen downstream of the converter. The output of
the downstream O2S will indicate limited activity in
this condition.
As the converter loses the ability to store oxygen,
the condition can be detected from the behavior of
the downstream O2S. When the efficiency drops, no
chemical reaction takes place. This means the con-
centration of oxygen will be the same downstream as
upstream. The output voltage of the downstream
O2S copies the voltage of the upstream sensor. The
only difference is a time lag (seen by the PCM)
between the switching of the O2S's.
To monitor the system, the number of lean-to-rich
switches of upstream and downstream O2S's is
counted. The ratio of downstream switches to
upstream switches is used to determine whether the
catalyst is operating properly. An effective catalyst
will have fewer downstream switches than it has
upstream switches i.e., a ratio closer to zero. For a
totally ineffective catalyst, this ratio will be one-to-
one, indicating that no oxidation occurs in the device.
The system must be monitored so that when cata-
lyst efficiency deteriorates and exhaust emissions
increase to over the legal limit, the MIL (check
engine lamp) will be illuminated.
Monitor OperationÐTo monitor catalyst effi-
ciency, the PCM expands the rich and lean switch
points of the heated oxygen sensor. With extended
switch points, the air/fuel mixture runs richer and
leaner to overburden the catalytic converter. Once
the test is started, the air/fuel mixture runs rich and
lean and the O2 switches are counted. A switch is
counted when an oxygen sensor signal goes from
below the lean threshold to above the rich threshold.
The number of Rear O2 sensor switches is divided by
the number of Front O2 sensor switches to determine
the switching ratio.
The test runs for 20 seconds. As catalyst efficiency
deteriorated over the life of the vehicle, the switch
rate at the downstream sensor approaches that of the
upstream sensor. If at any point during the test
25 - 4 EMISSIONS CONTROLRS
EMISSIONS CONTROL (Continued)

FUEL INJECTOR MECHANICAL MALFUNCTIONS
The PCM cannot determine if a fuel injector is
clogged, the needle is sticking or if the wrong injector
is installed. However, these could result in a rich or
lean condition causing the PCM to store a diagnostic
trouble code for either misfire, an oxygen sensor, or
the fuel system.
EXCESSIVE OIL CONSUMPTION
Although the PCM monitors engine exhaust oxygen
content when the system is in closed loop, it cannot
determine excessive oil consumption.
THROTTLE BODY AIR FLOW
The PCM cannot detect a clogged or restricted air
cleaner inlet or filter element.
VACUUM ASSIST
The PCM cannot detect leaks or restrictions in the
vacuum circuits of vacuum assisted engine control
system devices. However, these could cause the PCM
to store a MAP sensor diagnostic trouble code and
cause a high idle condition.
PCM SYSTEM GROUND
The PCM cannot determine a poor system ground.
However, one or more diagnostic trouble codes may
be generated as a result of this condition. The mod-
ule should be mounted to the body at all times,
including when diagnostics are performed.
PCM CONNECTOR ENGAGEMENT
The PCM may not be able to determine spread or
damaged connector pins. However, it might store
diagnostic trouble codes as a result of spread connec-
tor pins.
DESCRIPTION - MONITORED SYSTEMS
There are new electronic circuit monitors that
check fuel, emission, engine and ignition perfor-
mance. These monitors use information from various
sensor circuits to indicate the overall operation of the
fuel, engine, ignition and emission systems and thus
the emissions performance of the vehicle.
The fuel, engine, ignition and emission systems
monitors do not indicate a specific component prob-
lem. They do indicate that there is an implied prob-
lem within one of the systems and that a specific
problem must be diagnosed.
If any of these monitors detect a problem affecting
vehicle emissions, the Malfunction Indicator (Check
Engine) Lamp will be illuminated. These monitors
generate Diagnostic Trouble Codes that can be dis-
played with the a DRBIIItscan tool.
The following is a list of the system monitors:
²EGR Monitor (if equipped)²Misfire Monitor
²Fuel System Monitor
²Oxygen Sensor Monitor
²Oxygen Sensor Heater Monitor
²Catalyst Monitor
²Evaporative System Leak Detection Monitor (if
equipped)
Following is a description of each system monitor,
and its DTC.
Refer to the appropriate Powertrain Diagnos-
tics Procedures manual for diagnostic proce-
dures.
OXYGEN SENSOR (O2S) MONITOR
Effective 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 oper-
ating temperatures of 300É to 350ÉC (572É to 662ÉF),
the sensor generates a voltage that is inversely pro-
portional to the amount of oxygen in the exhaust.
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
²Reduced output voltage
²Dynamic shift
²Shorted or open circuits
Response rate is the time required for the sensor to
switch from lean to rich once it is exposed to a richer
than optimum A/F mixture or vice versa. As the sen-
sor starts malfunctioning, it could take longer to
detect the changes in the oxygen content of the
exhaust gas.
The output voltage of the O2S ranges from 0 to 1
volt (voltages are offset by 2.5 volts on NGC vehi-
cles). A good sensor can easily generate any output
voltage in this range as it is exposed to different con-
centrations of oxygen. To detect a shift in the A/F
mixture (lean or rich), the output voltage has to
change beyond a threshold value. A malfunctioning
sensor could have difficulty changing beyond the
threshold value.
OXYGEN SENSOR HEATER MONITOR
If there is an oxygen sensor (O2S) DTC as well as
a O2S heater DTC, the O2S heater fault MUST be
repaired first. After the O2S fault is repaired, verify
that the heater circuit is operating correctly.
25 - 6 EMISSIONS CONTROLRS
EMISSIONS CONTROL (Continued)