check engine CHRYSLER VOYAGER 2001 Service Manual

(9) Remove the seal from the discharge line fitting
and discard.
(10) Install plugs in, or tape over the opened dis-
charge line fitting and the compressor discharge port.
(11) Raise and support the vehicle.
(12) Remove the serpentine accessory drive belt
from the front of the engine. (Refer to 7 - COOLING/
ACCESSORY DRIVE/DRIVE BELTS - 2.4L -
REMOVAL) or (Refer to 7 - COOLING/ACCESSORY
DRIVE/DRIVE BELTS - 3.3L/3.8L - REMOVAL).
(13) Disconnect the engine wire harness connector
for the compressor clutch coil from the coil pigtail
wire connector on the top of the compressor (Fig. 1)
or (Fig. 2).
(14) On models with the 3.3L and 3.8L engines,
disengage the retainer on the engine wire harness
compressor clutch coil take out from the bracket on
the top of the compressor.
(15) On models with the 2.4L engine, remove the
four screws that secure the compressor to the mount-
ing bracket on the engine.
(16) On models with the 3.3L and 3.8L engines,
remove the three screws and one nut that secure the
compressor to the engine.
(17) Remove the compressor from the engine com-
partment.
NOTE: If a replacement compressor is being
installed, be certain to drain and measure the refrig-
erant oil contained in the removed compressor.
This will determine how much oil the replacement
compressor must contain before it is installed.(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT/REFRIGERANT OIL - STAN-
DARD PROCEDURE - REFRIGERANT OIL LEVEL).
REMOVAL - COMPRESSOR MOUNTING
BRACKET - 2.4L ENGINE
(1) Remove the compressor from the mounting
bracket. (Refer to 24 - HEATING & AIR CONDI-
TIONING/PLUMBING/COMPRESSOR - REMOVAL).
(2) Remove the four screws that secure the com-
pressor mounting bracket to the engine (Fig. 3).
(3) Remove the compressor mounting bracket from
the engine.
INSTALLATION - COMPRESSOR
NOTE: If a replacement compressor is being
installed, be certain to check the refrigerant oil
level. (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT/REFRIGERANT OIL - STAN-
DARD PROCEDURE - REFRIGERANT OIL LEVEL).
Use only refrigerant oil of the type recommended
for the compressor in the vehicle.
(1) Position the compressor into the engine com-
partment.
(2) On models with the 2.4L engine, loosely install
the four screws that secure the compressor to the
mounting bracket on the engine (Fig. 1). Tighten the
screws to 28 N´m (21 ft. lbs.).
Fig. 1 Compressor - 2.4L Engine
1 - CLUTCH COIL CONNECTOR
2 - DISCHARGE PORT
3 - COMPRESSOR
4 - SUCTION PORT
5 - SCREW (4)
6 - COMPRESSOR MOUNTING BRACKET
Fig. 2 Compressor - 3.3L/3.8L Engine
1 - STUD
2 - CLUTCH COIL CONNECTOR
3 - DISCHARGE PORT
4 - SCREW (2)
5 - SUCTION PORT
6 - COMPRESSOR
7 - SCREW
8 - NUT
24 - 66 PLUMBING - FRONTRS
COMPRESSOR (Continued)

INSTALLATION
NOTE: If the condenser is being replaced, add 30
milliliters (1 fluid ounce) of refrigerant oil to the
refrigerant system. Use only refrigerant oil of the
type recommended for the compressor in the vehi-
cle.
NOTE: Be certain that each of the radiator and con-
denser air seals are reinstalled in their proper loca-
tions. These air seals are required in order for the
air conditioning and engine cooling systems to per-
form as designed.
(1) Position the condenser to the right mounting
bracket and transmission oil cooler unit.
(2) Position the left mounting bracket onto the side
of the condenser and transmission oil cooler.
(3) Install and tighten the one screw that secures
the left mounting bracket to the side of the transmis-
sion oil cooler. Tighten the screw to 5 N´m (45 in.
lbs.).
(4) Install and tighten the two screws that secure
each mounting bracket to the sides of the condenser.
Tighten the screws to 5 N´m (45 in. lbs.).(5) Position the condenser, transmission oil cooler,
and mounting brackets into the vehicle as a unit. Be
certain that the locating pins that secure the mount-
ing brackets are engaged in the lower mount rubber
isolators on each side of the cooling module (Fig. 5).
(6) Install and tighten the two screws that secure
the top of the mounting bracket on each side of the
condenser to the cooling module. Tighten the screws
to 5 N´m (45 in. lbs.).
(7) Remove the tape or plugs from the condenser
outlet port and the liquid line fitting.
(8) Lubricate a new rubber O-ring seal with clean
refrigerant oil and install it on the liquid line fitting.
(9) Reconnect the liquid line fitting to the con-
denser outlet port on the right side of the cooling
module.
(10) Install and tighten the nut that secures the
liquid line fitting to the condenser. Tighten the nut to
23 N´m (17 ft. lbs.).
(11) Remove the tape or plugs from the condenser
inlet port and the discharge line fitting.
(12) Lubricate a new rubber O-ring seal with clean
refrigerant oil and install it on the discharge line fit-
ting.
(13) Reconnect the discharge line fitting to the
condenser inlet port on the right side of the cooling
module.
(14) Install and tighten the nut that secures the
discharge line fitting to the condenser. Tighten the
nut to 23 N´m (17 ft. lbs.).
(15) Reconnect the hoses to the transmission oil
cooler fittings on the left side of the cooling module.
(Refer to 7 - COOLING/TRANSMISSION/TRANS
COOLER LINES - INSTALLATION).
(16) Reposition the hood latch unit to the front of
the radiator closure panel crossmember.
(17) Install and tighten the two screws that secure
the hood latch unit to the front of the radiator clo-
sure panel crossmember. Check and adjust the hood
latch as needed. Tighten the screws to 14 N´m (123
in. lbs.).
(18) Position the radiator sight shield onto the
radiator closure panel crossmember (Fig. 4).
(19) Install and tighten the five small screws that
secure the front fascia grille inserts to the radiator
sight shield. Tighten the screws to 2 N´m (18 in. lbs.).
(20) Install and tighten the two large screws that
secure the front fascia and the outboard ends of the
radiator sight shield to the radiator closure panel
crossmember. Tighten the screws to 6 N´m (53 in.
lbs.).
(21) Evacuate the refrigerant system. (Refer to 24
- HEATING & AIR CONDITIONING/PLUMBING -
FRONT/REFRIGERANT - STANDARD PROCE-
DURE - REFRIGERANT SYSTEM EVACUATE).
Fig. 5 Condenser Mounting
1 - SCREW (2)
2 - LOWER MOUNT ISOLATOR (2)
3 - CONDENSER
RSPLUMBING - FRONT24-69
CONDENSER (Continued)

NOTE: When connecting the service equipment
couplings to the refrigerant system service ports,
be certain that the valve of each coupling is fully
closed. This will reduce the amount of effort
required to make the connection.
(1) Remove the caps from the refrigerant system
service ports and attach a manifold gauge set or a
R-134a refrigerant recovery/recycling/charging sta-
tion that meets SAE Standard J2210 to the refriger-
ant system.
(2) Attach a clamp-on thermocouple to the liquid
line. The thermocouple must be placed as close to the
A/C pressure transducer as possible to accurately
observe liquid line temperature.
(3) Bring the refrigerant system up to operating
temperature and pressure. This is done by allowing
the engine to run at idle under the following condi-
tions for five minutes.
(a) Front windows are open.
(b) Transaxle in Park.
(c) Front heater-A/C controls set to outside air,
full cool, panel mode, blower high, and compressor
engaged.
(d) If the vehicle is so equipped, the rear heater-
A/C controls must be set to full cool and blower
high.(4) Raise the liquid line (discharge) pressure to
about 1793 kPa (260 psi) by placing a piece of card-
board over part of the front side of the condenser. To
place the cardboard properly, remove the upper radi-
ator sight shield from the front fascia. Cover only
enough of the condenser to raise and maintain the
liquid line pressure at the specified level.
(5) Observe the liquid line (discharge) pressure
and liquid line temperature. Using the Charge Deter-
mination Chart (Fig. 31), determine whether the
refrigerant system is operating within the Proper
Charge Range.
(a) If the refrigerant system is operating in the
Undercharged area of the chart, add 0.057 kilo-
gram (0.125 pound or 2 ounces) of refrigerant to
the system.
(b) If the refrigerant system is operating in the
Overcharged area of the chart, reclaim 0.057 kilo-
gram (0.125 pound or 2 ounces) of refrigerant from
the system.
(6) Recheck the system charge level following each
refrigerant adjustment. Continue this process until
the system readings are in the Proper Charge Range
area on the Charge Determination Chart.
Fig. 31 Charge Determination Chart, Ambient Test Condition 85ÉF
24 - 88 PLUMBING - FRONTRS
REFRIGERANT (Continued)

ND-8 PAG refrigerant oil. Use only refrigerant oil of
this same type to service the refrigerant system.
OPERATION
After performing any refrigerant recovery or recy-
cling operation, always replenish the refrigerant sys-
tem with the same amount of the recommended
refrigerant oil as was removed. Too little refrigerant
oil can cause compressor damage, and too much can
reduce air conditioning system performance. PAG
refrigerant oil is much more hygroscopic than min-
eral oil, and will absorb any moisture it comes into
contact with, even moisture in the air. The PAG oil
container should always be kept tightly capped until
it is ready to be used. After use, recap the oil con-
tainer immediately to prevent moisture contamina-
tion.
STANDARD PROCEDURE - REFRIGERANT OIL
LEVEL
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - A/C PLUMBING)
and (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - CAUTION - A/C PLUMBING).
When an air conditioning system is assembled at
the factory, all components except the compressor are
refrigerant oil free. After the refrigerant system has
been charged and operated, the refrigerant oil in the
compressor is dispersed throughout the refrigerant
system. The receiver/drier, evaporator, condenser, and
compressor will each retain a significant amount of
the needed refrigerant oil.
It is important to have the correct amount of oil in
the refrigerant system. This ensures proper lubrica-
tion of the compressor. Too little oil will result in
damage to the compressor. Too much oil will reduce
the cooling capacity of the air conditioning system.
It will not be necessary to check the oil level in the
compressor or to add oil, unless there has been an oil
loss. An oil loss may occur due to a rupture or leak
from a refrigerant line, a connector fitting, a compo-
nent, or a component seal. If a leak occurs, add 30
milliliters (1 fluid ounce) of refrigerant oil to the
refrigerant system after the repair has been made.
Refrigerant oil loss will be evident at the leak point
by the presence of a wet, shiny surface around the
leak.
Refrigerant oil must be added when an receiver/
drier, evaporator or condenser is replaced. See the
Refrigerant Oil Capacities chart for the proper
amount of refrigerant oil to add. When a compressoris replaced, the refrigerant oil must be drained from
the old compressor and measured. Drain all of the
refrigerant oil from the new compressor, then fill the
new compressor with the same amount of fresh new
refrigerant oil that was drained out of the old com-
pressor.
REFRIGERANT OIL CAPACITIES
Front A/C Front & Rear
A/C
COMPONENT ml fl oz ml fl oz
Compressor 150 5.0 220 7.4
Filter-Drier 30 1.0 30 1.0
Condenser 30 1.0 30 1.0
Front Evaporator 60 2.0 60 2.0
Rear Evap. (including
underbody lines)N/A N/A 60 2.0
Compressor Drain and measure the oil
from the old compressor -
See text above.
SUCTION LINE
REMOVAL
The front air conditioner suction line includes the
low side service port on a section of tubing located
near the compressor. On models equipped with the
optional rear air conditioner, the front air conditioner
suction line also includes a suction line hose and
tube extension that connects the front suction line to
the suction line for the rear air conditioner.
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - A/C PLUMBING)
and (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - CAUTION - A/C PLUMBING).
(1) Recover the refrigerant from the refrigerant
system. (Refer to 24 - HEATING & AIR CONDI-
TIONING/PLUMBING - FRONT/REFRIGERANT -
STANDARD PROCEDURE - REFRIGERANT
RECOVERY).
(2) Disconnect and isolate the battery negative
cable.
(3) Remove the air cleaner top cover and snorkel
from the air cleaner housing located on the right side
of the engine compartment.
(4) Disconnect the drain tube from the wiper mod-
ule drain on the right side of the engine compart-
ment.
24 - 92 PLUMBING - FRONTRS
REFRIGERANT OIL (Continued)

(2) Take the proper precautions to protect the car-
peting below the rear heater core from spilled engine
coolant and have absorbent toweling readily avail-
able to mop up any spills.
(3) Insert the small end of an appropriate funnel
into the upper hose fitting of the heater core (Fig. 5).
(4) Carefully pour the proper pre-mixed engine
coolant solution into the rear heater core through a
funnel until coolant begins to appear at the lower
hose fitting of the heater core.
(5) Use absorbent toweling to clean up any engine
coolant spills from the preceding operation.
(6) Reconnect the heater hoses to the rear heater
core. (Refer to 24 - HEATING & AIR CONDITION-
ING/PLUMBING - REAR/HEATER HOSE - INSTAL-
LATION).
(7) Refill the engine cooling system. (Refer to 7 -
COOLING - STANDARD PROCEDURE - COOLING
SYSTEM REFILL).
THERMAL CYCLING
If the rear heater core was emptied and was not
pre-filled, it will be necessary to thermal cycle the
vehicle at least two times to ensure that the rear
heater core is properly filled.
(1) Refill the engine cooling system. (Refer to 7 -
COOLING - STANDARD PROCEDURE - COOLING
SYSTEM REFILL).
(2) Start the engine and allow it to operate until
the thermostat opens.
(3) Turn the engine off and allow it to cool.
(4) With the engine cold and not running, check
and top off the engine coolant level as necessary.
(Refer to 7 - COOLING - STANDARD PROCEDURE
- COOLANT LEVEL CHECK) and (Refer to 7 -
COOLING - STANDARD PROCEDURE - COOLANT
- ADDING).(5) Start the engine and allow it to operate until
the thermostat opens again.
(6) Turn the engine off and allow it to cool down
again.
(7) With the engine cold and not running, check
and top off the engine coolant level as necessary.
(Refer to 7 - COOLING - STANDARD PROCEDURE
- COOLANT LEVEL CHECK) and (Refer to 7 -
COOLING - STANDARD PROCEDURE - COOLANT
- ADDING).
(8) Check the performance of the rear heater.
Refer to REAR HEATER PERFORMANCE CHECK .
REAR HEATER PERFORMANCE CHECK
Successful completion of the rear heater perfor-
mance check will confirm that the rear heater core is
properly filled with engine coolant. If the check is not
successful, either there is still air trapped in the rear
heater core or the rear heater plumbing is restricted.
This check should be performed with the vehicle in a
shop where the ambient temperature is about 21É C
(70É F).
(1) Start the engine and allow it to idle until it
warms up to normal operating temperature.
(2) Adjust the heater-A/C controls so that the front
heater is turned Off, the rear heater is set for full
Heat, and the rear blower motor is at its highest
speed setting.
(3) Use an accurate test thermometer to measure
the temperature of the air being discharged from the
rear heater outlet located at the base of the right
C-pillar.
(4) Proper discharge air temperature readings
should be from 57É to 63É C (135É to 145É F).
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 FRONT - WARNING - HEATER PLUMB-
ING).
(1) Drain the engine cooling system. (Refer to 7 -
COOLING - STANDARD PROCEDURE - COOLING
SYSTEM DRAIN).
(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 rear heater distribution duct from
the right quarter inner panel. (Refer to 24 - HEAT-
ING & AIR CONDITIONING/DISTRIBUTION -
REAR/REAR HEATER DISTRIBUTION DUCT -
REMOVAL).
Fig. 5 Pre-Filling Heater Core - Typical
1 - REAR HEATER CORE
RSPLUMBING - REAR24 - 101
HEATER CORE (Continued)

(4) Raise the liquid line (discharge) pressure to
about 1793 kPa (260 psi) by placing a piece of card-
board over part of the front side of the condenser. To
place the cardboard properly, remove the upper radi-
ator sight shield from the front fascia. Cover only
enough of the condenser to raise and maintain the
liquid line pressure at the specified level.
(5) Observe the liquid line (discharge) pressure
and liquid line temperature. Using the Charge Deter-
mination Chart (Fig. 3), determine whether the
refrigerant system is operating within the Proper
Charge Range.
(a) If the refrigerant system is operating in the
Undercharged area of the chart, add 0.057 kilo-
gram (0.125 pound or 2 ounces) of refrigerant to
the system.
(b) If the refrigerant system is operating in the
Overcharged area of the chart, reclaim 0.057 kilo-
gram (0.125 pound or 2 ounces) of refrigerant from
the system.
(6) Recheck the system charge level following each
refrigerant adjustment. Continue this process until
the system readings are in the Proper Charge Range
area on the Charge Determination Chart (Fig. 3).DIESEL SUPPLEMENTAL
HEATER - DCHA
DESCRIPTION
Vehicles equipped with the optional diesel engine are
also equipped with a supplemental heater unit. This
unit is mounted under the vehicle and operates similar
to an oil fired furnace. The heater burns small
amounts of fuel to provide additional heat to the cool-
ant. Coolant is routed from the engine, to the supple-
mental heater, and then to the front heater core. This
provides additional heat to the passenger compart-
ment. The system is interfaced to the vehicles on-board
computer systems and DRB-III diagnostics.
Fig. 3 Charge Determination Chart, Ambient Test Condition 85ÉF
RGHEATING & AIR CONDITIONING24a-5
REFRIGERANT (Continued)

OPERATION
The supplemental heater unit is activated via the
temperature slide control or knob on the vehicle HVAC
control unit. If the control slide or knob is moved to or
above the upper set point the heater is activated. The
unit can operate in a full or partial load range as well
as an idle mode all dependent on the engine coolanttemperature. The heater unit will also turn off if the
HVAC temperature control is lowered to less than the
lower set point. The heater unit can take up to three
minutes to completely shut down when either the
heater temperature is set below the lower set point or
the vehicle ignition is shut down.
DIAGNOSIS AND TESTING - DIESEL SUPPLEMENTAL HEATER - DCHA
The following table lists possible fault symptoms of
diesel fueled heaters.
SYMPTOM POSSIBLE CAUSES
Smell of diesel fuel Check heater system integration in vehicle's fuel system. Check fuel
lines for leakage, kinks or obstructions. If OK, Inspect the inlet muffler,
drain as necessary. Re-test the unit and re-inspect. Inspect the
exhaust tube and heater unit for the presence of external fuel. If a
volume is observed on the unit or in the exhaust tube or after draining
and testing. Remove heater unit from vehicle and repair or replace
components as required.
Heater does not achieve full load
operation.Check heater operation with DRB-III and replace components as
required.
Continuous white smoke from heater
exhaust during combustion operation.Check heater operation with DRB-III and replace components as
required. White smoke is typical in extreme weather conditions.
Heater can not be switched off. Check heater operation with DRB-III and replace components as
required.
Heater does not operate. Diagnosis cabin heater ECU using the DRB-III and the procedures
listed in Vehicle Performance under Cabin Heater Diagnosis in Group
18.
Loss of coolant (Leakage) or heater
develops smoke during combustion
operation and exhaust has an
extremely sweet smell.Inspect coolant hoses for leakage, kinks or loose hose connection.
Inspect the exhaust tube assembly for continuous flow, if OK there is
an internal heater leak and unit should be inspected and components
should be replaced as required.
Loss of fuel (dripping). Check heater system integration in vehicles fuel system. Check fuel
line connection for leakage. If OK there is an internal leak and unit
should be inspected and replaced as required.
EXHAUST TUBE
REMOVAL
WARNING: THERE IS A POTENTIAL DANGER OF
SKIN BURNS AS THE HEATER AND ITS COMPO-
NENTS MAY BE VERY HOT. MAKE SURE THE
HEATER IS ALLOWED TO COOL DOWN BEFORE
ANY SERVICE WORK IS ATTEMPTED.
WARNING: THERE IS A POTENTIAL DANGER OF
SKIN BURNS AS THE EXHAUST SYSTEM MAY BE
VERY HOT. MAKE SURE THE EXHAUST SYSTEM ISALLOWED TO COOL DOWN BEFORE ANY SERVICE
WORK IS ATTEMPTED ON THE CABIN HEATER.
(1) Elevate vehicle on a lift taking note of the
exhaust tube flexible section.
(2) Remove the exhaust clamp at the flexible pipe
and steel pipe connection (Fig. 4).
(3) Remove the clamp at the flexible pipe connec-
tion and the heater unit housing (if required).
(4) Remove the three screws holding the exhaust
pipe to the body.
(5) Remove the steel exhaust pipe from the vehi-
cle.
(6) Remove the flexible exhaust pipe from the
vehicle (if required).
24a - 6 HEATING & AIR CONDITIONINGRG
DIESEL SUPPLEMENTAL HEATER - DCHA (Continued)

EMISSIONS CONTROL
TABLE OF CONTENTS
page page
EMISSIONS CONTROL
DESCRIPTION............................1
OPERATION.............................8EVAPORATIVE EMISSIONS.................10
EXHAUST GAS RECIRCULATION............20
ON-BOARD DIAGNOSTICS.................23
EMISSIONS CONTROL
DESCRIPTION - MONITORED COMPONENT
There are several components that will affect vehi-
cle emissions if they malfunction. If one of these com-
ponents malfunctions the Malfunction Indicator
Lamp (Check Engine) will illuminate.
Some of the component monitors are checking for
proper operation of the part. Electrically operated
components now have input (rationality) and output
(functionality) checks. Previously, a component like
the Throttle Position sensor (TPS) was checked by
the PCM for an open or shorted circuit. If one of
these conditions occurred, a DTC was set. Now there
is a check to ensure that the component is working.
This is done by watching for a TPS indication of a
greater or lesser throttle opening than MAP and
engine rpm indicate. In the case of the TPS, if engine
vacuum is high and engine rpm is 1600 or greater
and the TPS indicates a large throttle opening, a
DTC will be set. The same applies to low vacuum
and 1600 rpm.Any component that has an associated
limp in will set a fault after 1 trip with the malfunc-
tion present.
Refer to the Diagnostic Trouble Codes Description
Charts in this section and the appropriate Power-
train Diagnostic Procedure Manual for diagnostic
procedures.
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 Air Temperature (IAT) Sensor
²Throttle Position (TPS) Sensor
²Ambient/Battery Temperature Sensors
²Power Steering Switch
²Oxygen Sensor Heater
²Engine Controller
²Brake Switch
²Leak Detection Pump Switch
²P/N Switch
²Trans Controls
Output FunctionalityÐPCM outputs are tested
for functionality in addition to testing for opens and
shorts. When the PCM provides a voltage to an out-
RSEMISSIONS CONTROL25-1

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
²Torque Converter Clutch Solenoid
²Idle Air Control
²Purge Solenoid
²EGR Solenoid
²LDP Solenoid
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.
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, 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
'Big Slope'. 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. 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 a Freeze Frame 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 (automatic 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
²Closed throttle speed
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
25 - 2 EMISSIONS CONTROLRS
EMISSIONS CONTROL (Continued)

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
period the switch ratio reaches a predetermined
value, a counter is incremented by one. The monitor
is enabled to run another test during that trip. When
the test fails three times, the counter increments to
three, a malfunction is entered, and a Freeze Frame
is stored. When the counter increments to three dur-ing the next trip, the code is matured and the MIL is
illuminated. If the test passes the first, no further
testing is conducted during that trip.
The MIL is extinguished after three consecutive
good trips. The good trip criteria for the catalyst
monitor is more stringent than the failure criteria. In
order to pass the test and increment one good trip,
the downstream sensor switch rate must be less than
80% of the upstream rate (60% for manual transmis-
sions). The failure percentages are 90% and 70%
respectively.
Enabling ConditionsÐThe following conditions
must typically be met before the PCM runs the cat-
alyst monitor. Specific times for each parameter may
be different from engine to engine.
²Accumulated drive time
²Enable time
²Ambient air temperature
²Barometric pressure
²Catalyst warm-up counter
²Engine coolant temperature
²Accumulated throttle position sensor
²Vehicle speed
²MAP
²RPM
²Engine in closed loop
²Fuel level
Pending ConditionsÐ
²Misfire DTC
²Front Oxygen Sensor Response
²Front Oxygen Sensor Heater Monitor
²Front Oxygen Sensor Electrical
²Rear Oxygen Sensor Rationality (middle check)
²Rear Oxygen Sensor Heater Monitor
²Rear Oxygen Sensor Electrical
²Fuel System Monitor
²All TPS faults
²All MAP faults
²All ECT sensor faults
²Purge flow solenoid functionality
²Purge flow solenoid electrical
²All PCM self test faults
²All CMP and CKP sensor faults
²All injector and ignition electrical faults
²Idle Air Control (IAC) motor functionality
²Vehicle Speed Sensor
²Brake switch
²Intake air temperature
ConflictÐThe catalyst monitor does not run if any
of the following are conditions are present:
²EGR Monitor in progress
²Fuel system rich intrusive test in progress
²EVAP Monitor in progress
²Time since start is less than 60 seconds
²Low fuel level
²Low ambient air temperature
25 - 4 EMISSIONS CONTROLRS
EMISSIONS CONTROL (Continued)