2005 CHRYSLER CARAVAN air condition

(3) Remove retaining nut from heater line under
hood bracket.
(4) Raise and support the vehicle. Take note of the
location of the flexible section of the cabin heater
exhaust tube.
(5) Remove the clamps from cabin heater lines to
the rubber connection nearest the tubes. Separate
the hoses from the tube assembly leaving the rubber
hose attached to the cabin heater.
(6) Remove the cabin heater intake pipe from the
heater unit (Refer to 24 - HEATING & AIR CONDI-
TIONING/CABIN HEATER/INLET HOSE -
REMOVAL) (Fig. 7).
(7) Remove heater pipe assembly retaining screws
and remove assembly from vehicle.INSTALLATION
(1) Position the heater pipe assembly and install
the retaining screws.
(2) Install the heater unit intake pipe to the
heater unit (Refer to 24 - HEATING & AIR CONDI-
TIONING/CABIN HEATER/INLET HOSE - INSTAL-
LATION).
(3) Connect heater hoses to the heater unit and
tighten the clamps.
(4) Install heater unit intake pipe to heater unit
(Refer to 24 - HEATING & AIR CONDITIONING/
CABIN HEATER/INLET HOSE - INSTALLATION).
(5) Lower the vehicle.
(6) Install and tighten the retaining nut to the
heater line under the hood bracket.
Fig. 6 Cabin Heater Pipes
1 - HEATER CORE INTAKE PIPE
2 - HEATER CORE RETURN PIPE
3 - A/C LINES
4 - A/C EXPANSION VALVE5 - A/C EXPANSION VALVE GROUND WIRE
6 - CABIN HEATER RETURN PIPE
7 - CABIN HEATER INTAKE PIPE
8 - CABIN HEATER PIPES RETAINING NUT
24 - 120 CABIN HEATERRS
HEATER PIPES (Continued)

(7) Connect the heater lines to the heater hoses at
the heater core and EGR port. Position spring clamps
onto the hoses.
(8) Fill the engine cooling system (Refer to 7 -
COOLING - STANDARD PROCEDURE).
HEATER UNIT
REMOVAL
WARNING: DO NOT OPERATE THE DIESEL SUP-
PLEMENTAL CABIN HEATER IN AN ENCLOSED
AREA SUCH AS A GARAGE THAT DOES NOT HAVE
EXHAUST VENTILATION FACILITIES. ALWAYS VENT
THE CABIN HEATER EXHAUST WHEN OPERATING
THE CABIN HEATER. ALLOW THE DIESEL SUPPLE-
MENTAL CABIN HEATER TO COOL BEFORE PER-
FORMING ANY SERVICE PROCEDURES TO THE
CABIN HEATER. VERIFY THAT ALL DIESEL SUP-
PLEMENTAL CABIN HEATER FUEL LINES ARE
SECURELY FASTENED TO THEIR RESPECTIVE
COMPONENTS BEFORE PERFORMING ANY SER-
VICE PROCEDURES TO THE CABIN HEATER. FAIL-
URE TO FOLLOW THESE INSTRUCTION MAY
RESULT IN PERSONAL INJURY OR DEATH.(1) Raise and support the vehicle. Take note of the
location of the flexible section of the cabin heater
exhaust tube.
(2) Drain the engine cooling system (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(3) Carefully open one hose to the underbody tube
assembly and drain the remaining coolant. A salvage
hose is a good idea to control the residual coolant, as
flow will occur from both the cabin heater and the
hose and tube assemblies.
(4) Remove the second hose from the underbody
hose and tube assembly.
(5) Loosen the hose and tube assembly from the
toe-board crossmember at two locations.
(6) Disconnect the electrical connector from the
body harness near the toe-board crossmember and
rail.
(7) Remove the wiring harness from the toe-board
crossmember (Refer to 24 - HEATING & AIR CON-
DITIONING/CABIN HEATER/HEATER UNIT -
REMOVAL).
(8) Open the fuel filler cap. Disconnect the rubber
fuel hose between the body tube assembly and the
fuel pump nipple at the body tube joint. A minimal
amount of fuel may flow from the open port.
NOTE: Utilize an approved fuel storage container to
catch any residual fuel.
(9) Loosen the two fasteners at the rail. Take care
to notice that the exhaust tube bracket tab is on top
of the heater bracket and that there are two spacer
washers installed between the rubber grommets.
(10) Remove the flexible section of the cabin
heater exhaust tube from the exhaust tube by loos-
ening the clamp. Remove the hose from the exhaust
tube. Removal of the rail tube assembly may aid in
this service operation (Refer to 24 - HEATING & AIR
CONDITIONING/CABIN HEATER/EXHAUST TUBE
- REMOVAL).
(11) Remove seat hex nut at the heater mounting
flange to crossmember.
(12) Loosen the remaining fasteners which mount
the exhaust tube assembly to the vehicle.
(a) Install a suitable support device under the
cabin heater and secure the cabin heater to the
support.
(13) Loosen the remaining three fasteners to the
crossmembers.
(14) Remove the loosened fasteners that support
the cabin heater while supporting the weight of the
heater.
(15) Swing the cabin heater mounting bracket
from between the exhaust bracket and rail mounting
location. Drain any residual coolant from the cabin
heater.
Fig. 7 Cabin Heater Air Intake And Heater Pipe
Assembly
1 - INTAKE TUBE AIR INTAKE
2 - INTAKE PIPE
3 - RETAINING SCREWS
4 - INTAKE HEATER LINE
5 - RETURN HEATER LINE
RSCABIN HEATER24 - 121
HEATER PIPES (Continued)

(16) Remove the cabin heater from the vehicle.
INSTALLATION
(1) Install the cabin heater mounting bracket
between the exhaust bracket and the rail mounting
location.
(2) Support the cabin heater and install the fasten-
ers that secure the cabin heater to the mounting
bracket.
(3) Install the three fasteners to the crossmem-
bers. Tighten the M6 fasteners to 7 N´m (62 in. lbs.).
(4) Position the two spacer washers between the
body and the rubber grommets for the two mounting
points on the rail.
(5) Tighten the remaining M6 fasteners to 7 N´m
(62 in. lbs.) and the M8 fasteners to 23 N´m (17 ft.
lbs.) which mount the exhaust tube assembly to the
vehicle.
(6) Install the seat hex nut at the heater mounting
flange to the crossmembers. Tighten the nut to 60
N´m (44 ft. lbs.)
(7) Install the flexible section of the cabin heater
exhaust tube to the exhaust tube. Tighten the M6
bolt of the clamp securley. Install the hose to the
exhaust tube.
(8) Tighten the two M8 fasteners at the rail to 23
N´m (17 ft. lbs.). Taking care so that the exhaust
tube bracket tab is on the top of the heater bracket.
(9) Install the wiring harness (Refer to 24 - HEAT-
ING & AIR CONDITIONING/CABIN HEATER/
HEATER UNIT - INSTALLATION).
(10) Tighten the hose and tube assembly to the
toe-board crossmember at two locations.
(11) Install the second hose to the underbody hose
and tube assembly.
(12) Connect the rubber fuel hose between the
body tube assembly and the fuel pump nipple at the
body tube joint. Close the fuel fill cap.
(13) Remove the cabin heater support device from
under the vehicle.
(14) Lower the vehicle.(15) Fill the engine cooling system (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(16) Verify function of the cabin heater.
HEATER WIRING
REMOVAL
(1) Elevate vehicle on a lift taking note of the
exhaust tube flexible section.
(2) Unplug connector from vehicle wiring harness
to cabin heater harness.
(3) Unplug connector from cabin heater harness to
dosing pump connector.
(4) Unplug two connectors from cabin heater har-
ness to cabin heater controller connectors.
(5) Remove two wiring harness connectors from
underbody.
(6) Remove two wiring harness connectors from
cabin heater shield.
(7) Carefully route the cabin heater harness to the
left side between the cabin heater unit and the cabin
heater shield.
INSTALLATION
(1) Carefully route the cabin heater harness from
the left side of the cabin heater between the cabin
heater unit and the cabin heater shield.
(2) Install the two wiring harness retaining con-
nectors to the cabin heater shield.
(3) Route the wiring harness along the underside
of the vehicle and install the two wiring harness
retaining connectors.
(4) Plug the two connectors from the cabin heater
harness to the cabin heater controller.
(5) Plug the connector to the cabin heater harness
to the dosing pump connector.
(6) Plug the connector from the vehicle wiring har-
ness to the cabin heater harness.
(7) Lower the vehicle.
(8) Verify function of the cabin heater.
24 - 122 CABIN HEATERRS
HEATER UNIT (Continued)

EMISSIONS CONTROL
TABLE OF CONTENTS
page page
EMISSIONS CONTROL
DESCRIPTION
VEHICLE EMISSION CONTROL
INFORMATION LABEL...................1
TRIP DEFINITION......................1
DESCRIPTION - MONITORED COMPONENT . 1
NON-MONITORED CIRCUITS.............5
DESCRIPTION - MONITORED SYSTEMS....6HIGH AND LOW LIMITS.................9
OPERATION
SYSTEM.............................9
DRB IIITSTATE DISPLAY TEST MODE.....10
EVAPORATIVE EMISSIONS................11
EXHAUST GAS RECIRCULATION...........22
ON-BOARD DIAGNOSTICS................25
EMISSIONS CONTROL
DESCRIPTION
VEHICLE EMISSION CONTROL INFORMATION
LABEL
All models have a Vehicle Emission Control Infor-
mation (VECI) Label. Chrysler permanently attaches
the label in the engine compartment. It cannot be
removed without defacing information and destroying
the label.
The label contains the vehicle's emission specifica-
tions and vacuum hose routings. All hoses must be
connected and routed according to the label.
TRIP DEFINITION
A ªTripº means vehicle operation (following an
engine-off period) of duration and driving mode such
that all components and systems are monitored at
least once by the diagnostic system. The monitors
must successfully pass before the PCM can verify
that a previously malfunctioning component is meet-
ing the normal operating conditions of that compo-
nent. For misfire or fuel system malfunction, the
MIL may be extinguished if the fault does not recur
when monitored during three subsequent sequential
driving cycles in which conditions are similar to
those under which the malfunction was first deter-
mined.
Anytime the MIL is illuminated, a DTC is stored.
The DTC can self erase only after the MIL has been
extinguished. Once the MIL is extinguished, the
PCM must pass the diagnostic test for the most
recent DTC for 40 warm-up cycles (80 warm-up
cycles for the Fuel System Monitor and the Misfire
Monitor). A warm-up cycle can best be described by
the following:
²The engine must be running²A rise of 40ÉF in engine temperature must occur
from the time when the engine was started
²Engine coolant temperature must crossover
160ÉF
²A ªdriving cycleº that consists of engine start up
and engine shut off.
Once the above conditions occur, the PCM is con-
sidered to have passed a warm-up cycle. Due to the
conditions required to extinguish the MIL and erase
the DTC, it is most important that after a repair has
been made, all DTC's be erased and the repair veri-
fied by running 1±good trip.
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 as well as continuity tests
(opens/shorts). 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 malfunction present.
Refer to the Diagnostic Trouble Codes Description
Charts in this section and the appropriate Power-
train Diagnostic Procedure Manual for diagnostic
procedures.
RSEMISSIONS CONTROL25-1

The following is a list of the monitored compo-
nents:
²Catalyst Monitor
²Comprehensive Components
²EGR (if equipped)
²Fuel Control (rich/lean)
²Oxygen Sensor Monitor
²Oxygen Sensor Heater Monitor
²Purge
²Misfire
²Natural Vacuum Leak Detection (NVLD)
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. All will set a DTC and illuminate the MIL in 1-
trip.
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) (slow response)
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 Switch²Oxygen Sensor Heater
²Engine Controller
²Brake Switch
²Natural Vacuum Leak Detection (NVLD)
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-
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
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, misfire or
exhaust leak, the sensor produces a low voltage,
below 450 mV. When the oxygen 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, and purge.
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
25 - 2 EMISSIONS CONTROLRS
EMISSIONS CONTROL (Continued)

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. Many
times the condition is only temporey and the sensor
will recover. Under normal conditions the voltage sig-
nal surpasses the threshold, and a counter is incre-
mented 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 Signal 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 pressure²Engine RPM within acceptable range of desired
idle
²Closed throttle speed
Pending ConditionsÐThe Task Manager typi-
cally does not run the Oxygen Sensor Signal Monitor
if overlapping 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
²Intake 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
²Ethenal content learn is taking place and the
ethenal used once flag is set
SuspendÐThe Task Manager suspends maturing
a fault for the Oxygen Sensor Monitor if an of the fol-
lowing are present:
²Oxygen Sensor Heater Monitor, Priority 1
²Misfire Monitor, Priority 2
OXYGEN SENSOR HEATER MONITOR (NGC)
DESCRIPTIONÐIf the Oxygen sensor (O2S) DTC
as well as a O2S heater DTC is present, the O2S
Heater DTC MUST be repaired first. After the O2S
Heater is repaired, verify that the sensor circuit is
operating correctly.
The voltage reading taken from the O2S are very
temperature sensitive. The readings taken from the
O2S are not accurate below 300 degrees C. Heating
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. Starting
with the introduction on the NGC module the strat-
egy for checking the heater circuit has changed. The
heater resistance is checked by the NGC almost
immediately after the engine is started. The same
O2S heater return pin used to read the heater resis-
tance is capable of detecting an open circuit, a
shorted high or shorted low condition.
RSEMISSIONS CONTROL25-3
EMISSIONS CONTROL (Continued)

OXYGEN SENSOR HEATER MONITOR (SBEC)
DESCRIPTIONÐIf 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.
The voltage readings taken from the O2S are very
temperature sensitive. The readings are not accurate
below 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 directly. The
sensor output is used to test the heater by isolating
the effect of the heater element on the O2S output
voltage from the other effects. The resistance is nor-
mally 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 temperature decreases, the resistance increases
and the PCM detects a higher voltage at the refer-
ence signal. The O2S circuit is monitored for a drop
in voltage.
OPERATIONÐThe Oxygen Sensor Heater Moni-
tor begins after the ignition has been turned OFF
and the O2 sensors have cooled. 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 sen-
sor cools down, the resistance increases and the PCM
reads the increase in voltage. Once voltage has
increased to a predetermined amount, higher than
when the test started, the oxygen sensor is cool
enough to test heater operation.
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, after the 2nd failure.Enabling ConditionsÐThe following conditions
must be met for the PCM to run the oxygen sensor
heater test:
²Engine run time of at least 5.1 minutes
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 high oxygen
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.
25 - 4 EMISSIONS CONTROLRS
EMISSIONS CONTROL (Continued)

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 temperature²Accumulated 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
²Ethanel content learn is taking place and the
ethenal used once flag is set
SuspendÐThe Task Manager does not mature a
catalyst fault if any of the following are present:
²Oxygen Sensor Monitor, Priority 1
²Upstream Oxygen Sensor Heater, Priority 1
²EGR Monitor, Priority 1
²EVAP Monitor, Priority 1
²Fuel System Monitor, Priority 2
²Misfire Monitor, Priority 2
NON-MONITORED CIRCUITS
The PCM does not monitor all circuits, systems
and conditions that could have malfunctions causing
driveability problems. However, problems with these
systems may cause the PCM to store diagnostic trou-
ble codes for other systems or components. For exam-
ple, a fuel pressure problem will not register a fault
directly, but could cause a rich/lean condition or mis-
fire. This could cause the PCM to store an oxygen
sensor or misfire diagnostic trouble code.
RSEMISSIONS CONTROL25-5
EMISSIONS CONTROL (Continued)