2005 CHRYSLER CARAVAN check engine

(6) Refill the engine cooling system (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(7) Verify function of the cabin heater.
EXHAUST TUBE
REMOVAL
WARNING: THERE IS A POTENTIAL DANGER OF
SKIN BURNS AS THE SUPPLEMENTAL CABIN
HEATER AND ITS COMPONENTS MAY BE VERY
HOT. MAKE SURE THE CABIN HEATER IS
ALLOWED TO COOL DOWN BEFORE ANY SERVICE
WORK ON THE CABIN HEATER SYSTEM IS
ATTEMPTED.
(1) Raise and support the vehicle. Take note of the
location of the flexible section of the cabin heater
exhaust tube.
(2) Remove the exhaust clamp at the flexible pipe
and steel pipe connection (Fig. 3).
(3) Remove the clamp at the flexible pipe connec-
tion and the cabin heater 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).
INSTALLATION
(1) Install the flexible exhaust pipe to the cabin
heater. Tighten the mounting clamp securely.
(2) Position the steel exhaust pipe to the flexible
exhaust. Tighten the mounting clamp securely.
(3) Loosely install the three exhaust pipe screws
and adjust pipe placement as required. Tighten the
screws securely.
(4) Install the clamp that secures the steel exhaust
pipe to the flexible exhaust pipe. Tighten the clamp
securely.
(5) Check exhaust end placement of the exhaust
pipe and make any final adjustments.
(6) Lower the vehicle.
Fig. 3 Cabin Heater Exhaust System
1 - MOUNTING SCREWS (3)
2 - STEEL HEATER EXHAUST PIPE
3 - EXHAUST CLAMP (2)4 - FLEXIBLE HEATER EXHAUST PIPE
5 - CABIN HEATER AND SHIELD
6 - EXHAUST PIPE MOUNTING CLIPS (3) (IF EQUIPPED)
24 - 116 CABIN HEATERRS
AIR INTAKE PIPE (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)

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)

The major non-monitored circuits are listed below
along with examples of failures modes that do not
directly cause the PCM to set a DTC, but for a sys-
tem that is monitored.
FUEL PRESSURE
The fuel pressure regulator controls fuel system
pressure. The PCM cannot detect a clogged fuel
pump inlet filter, clogged in-line fuel filter, or a
pinched fuel supply or return line. However, these
could result in a rich or lean condition causing the
PCM to store an oxygen sensor, fuel system, or mis-
fire diagnostic trouble code.
SECONDARY IGNITION CIRCUIT
The PCM cannot detect an inoperative ignition coil,
fouled or worn spark plugs, ignition cross firing, or
open spark plug cables. The misfire will however,
increase the oxygen content in the exhaust, deceiving
the PCM in to thinking the fuel system is too lean.
Also see misfire detection. There are DTC's that can
detect misfire and Ionization shorts in the secondary
ignition circuit, refer to the Powertrain Diagnostic
manual for more information
CYLINDER COMPRESSION
The PCM cannot detect uneven, low, or high engine
cylinder compression. Low compression lowers O2
content in the exhaust. Leading to fuel system, oxy-
gen sensor, or misfire detection fault.
EXHAUST SYSTEM
The PCM cannot detect a plugged, restricted or
leaking exhaust system. It may set a EGR (if
equipped) or Fuel system or O2S fault.
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 PCMto 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 scan 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.
25 - 6 EMISSIONS CONTROLRS
EMISSIONS CONTROL (Continued)

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.
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 (572 É 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. This main-
tains a 14.7 to 1 Air Fuel (A/F) ratio. At this mixture
ratio, the catalyst works best to remove hydrocarbons
(HC), carbon monoxide (CO) and nitrogen oxide
(NOx) from the exhaust.
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 O2S circuit is monitored for a drop in voltage.
The sensor output is used to test the heater by iso-
lating the effect of the heater element on the O2S
output voltage from the other effects.
EGR MONITOR (if equipped)
The Powertrain Control Module (PCM) performs
an on-board diagnostic check of the EGR system.
The EGR monitor is used to test whether the EGR
system is operating within specifications. The diag-
nostic check activates only during selected engine/
driving conditions. When the conditions are met, the
EGR is turned off (solenoid energized) and the O2S
compensation control is monitored. Turning off the
EGR shifts the air fuel (A/F) ratio in the lean direc-
tion. The O2S data should indicate an increase in the
O2 concentration in the combustion chamber when
the exhaust gases are no longer recirculated. While
this test does not directly measure the operation of
the EGR system, it can be inferred from the shift in
the O2S data whether the EGR system is operating
correctly. Because the O2S is being used, the O2S
test must pass its test before the EGR test. Also
looks at EGR linear potentiometer for feedback.
MISFIRE MONITOR
Excessive engine misfire results in increased cata-
lyst temperature and causes an increase in HC emis-
sions. Severe misfires could cause catalyst damage.
To prevent catalytic convertor damage, the PCM
monitors engine misfire.
The Powertrain Control Module (PCM) monitors
for misfire during most engine operating conditions
(positive torque) by looking at changes in the crank-
shaft speed. If a misfire occurs the speed of the
crankshaft will vary more than normal.
FUEL SYSTEM 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. The catalyst works best
when the air fuel (A/F) ratio is at or near the opti-
mum of 14.7 to 1.
The PCM is programmed to maintain the optimum
air/fuel ratio. This is done by making short term cor-
rections in the fuel injector pulse width based on the
O2S output. The programmed memory acts as a self
calibration tool that the engine controller uses to
compensate for variations in engine specifications,
sensor tolerances and engine fatigue over the life
span of the engine. By monitoring the actual air-fuel
ratio with the O2S (short term) and multiplying that
with the program long-term (adaptive) memory and
comparing that to the limit, it can be determined
whether it will pass an emissions test. If a malfunc-
RSEMISSIONS CONTROL25-7
EMISSIONS CONTROL (Continued)

tion occurs such that the PCM cannot maintain the
optimum A/F ratio, then the MIL will be illuminated.
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's 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.NATURAL VACUUM LEAK DETECTION (NVLD) (if equipped)
The Natural Vacuum Leak Detection (NVLD) sys-
tem is the next generation evaporative leak detection
system that will first be used on vehicles equipped
with the Next Generation Controller (NGC). This
new system replaces the leak detection pump as the
method of evaporative system leak detection. This is
to detect a leak equivalent to a 0.0209(0.5 mm) hole.
This system has the capability to detect holes of this
size very dependably.
The basic leak detection theory employed with
NVLD is the9Gas Law9. This is to say that the pres-
sure in a sealed vessel will change if the temperature
of the gas in the vessel changes. The vessel will only
see this effect if it is indeed sealed. Even small leaks
will allow the pressure in the vessel to come to equi-
librium with the ambient pressure. In addition to the
detection of very small leaks, this system has the
capability of detecting medium as well as large evap-
orative system leaks.
The NVLD seals the canister vent during engine
off conditions. If the EVAP system has a leak of less
than the failure threshold, the evaporative system
will be pulled into a vacuum, either due to the cool
down from operating temperature or diurnal ambient
temperature cycling. The diurnal effect is considered
one of the primary contributors to the leak determi-
nation by this diagnostic. When the vacuum in the
system exceeds about 19H2O (0.25 KPA), a vacuum
switch closes. The switch closure sends a signal to
the NGC. The NGC, via appropriate logic strategies
(described below), utilizes the switch signal, or lack
thereof, to make a determination of whether a leak is
present.
The NVLD device is designed with a normally open
vacuum switch, a normally closed solenoid, and a
seal, which is actuated by both the solenoid and a
diaphragm. The NVLD is located on the atmospheric
vent side of the canister. The NVLD assembly may
be mounted on top of the canister outlet, or in-line
between the canister and atmospheric vent filter. The
normally open vacuum switch will close with about 19
H2O (0.25 KPA) vacuum in the evaporative system.
The diaphragm actuates the switch. This is above the
opening point of the fuel inlet check valve in the fill
tube so cap off leaks can be detected. Submerged fill
systems must have recirculation lines that do not
have the in-line normally closed check valve that pro-
tects the system from failed nozzle liquid ingestion,
in order to detect cap off conditions.
The normally closed valve in the NVLD is intended
to maintain the seal on the evaporative system dur-
ing the engine off condition. If vacuum in the evapo-
rative system exceeds 39to 69H2O (0.75 to 1.5 KPA),
the valve will be pulled off the seat, opening the seal.
This will protect the system from excessive vacuum
25 - 8 EMISSIONS CONTROLRS
EMISSIONS CONTROL (Continued)