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 “Trip” 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:

• The engine must be running

• A rise of 40°F in engine temperature must occur

from the time when the engine was started

• Engine coolant temperature must crossover

160°F

• A “driving cycle” 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.

EMISSIONS CONTROL

25 - 1

The following is a list of the monitored compo-

nents:

• Catalyst Monitor

• Comprehensive Components

• EGR (if equipped)

• Fuel Control (rich/lean)

• Oxygen Sensor Monitor

• Oxygen Sensor Heater Monitor

• Purge

• Misfire

• Natural 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 for functionality.
Methods for monitoring the various Comprehensive
Component monitoring include:

(1) Circuit Continuity
• Open

• Shorted high

• Shorted to ground
(2) Rationality or Proper Functioning
• Inputs tested for rationality

• Outputs 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 Rationality—While 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:

• Manifold Absolute Pressure (MAP) Sensor

• Oxygen Sensor (O2S) (slow response)

• Engine Coolant Temperature (ECT) Sensor

• Camshaft Position (CMP) Sensor

• Vehicle Speed Sensor

• Crankshaft Position (CKP) Sensor

• Intake Air Temperature (IAT) Sensor

• Throttle Position (TPS) Sensor

• Ambient/Battery Temperature Sensors

• Power Steering Switch

• Oxygen Sensor Heater

• Engine Controller

• Brake Switch

• Natural Vacuum Leak Detection (NVLD)

• P/N Switch

• Trans Controls
Output Functionality—PCM 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:
• Fuel Injectors

• Ignition Coils

• Torque Converter Clutch Solenoid

• Idle Air Control

• Purge Solenoid

• EGR Solenoid

• Radiator Fan Control

• Trans Controls

OXYGEN SENSOR (O2S) MONITOR

DESCRIPTION—Effective

control

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 300° to 350°C
(572° to 662°F), 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:

• Slow response rate (Big Slope)

• Reduced output voltage (Half Cycle)

• Heater Performance
Slow Response Rate (Big Slope)—Response 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 CONTROL

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)—The

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 Performance—The heater is tested by a

separate monitor. Refer to the Oxygen Sensor Heater
Monitor.

OPERATION—As

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 Conditions—The following conditions

must typically be met for the PCM to run the oxygen
sensor monitor:

• Battery voltage

• Engine temperature

• Engine run time

• Engine run time at a predetermined speed

• Engine run time at a predetermined speed and

throttle opening

• Transmission in gear (automatic only)

• Fuel system in Closed Loop

• Long Term Adaptive (within parameters)

• Power Steering Switch in low PSI (no load)

• Engine at idle

• Fuel level above 15%

• Ambient air temperature

• Barometric pressure

• Engine RPM within acceptable range of desired

idle

• Closed throttle speed
Pending Conditions—The 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:

• Misfire Monitor

• Front Oxygen Sensor and Heater Monitor

• MAP Sensor

• Vehicle Speed Sensor

• Engine Coolant Temperature Sensor

• Throttle Position Sensor

• Engine Controller Self Test Faults

• Cam or Crank Sensor

• Injector and Coil

• Idle Air Control Motor

• EVAP Electrical

• EGR Solenoid Electrical

• Intake Air Temperature

• 5 Volt Feed
Conflict—The Task Manager does not run the

Oxygen Sensor Monitor if any of the following condi-
tions are present:

• A/C ON (A/C clutch cycling temporarily sus-

pends monitor)

• Purge flow in progress

• Ethenal content learn is taking place and the

ethenal used once flag is set

Suspend—The Task Manager suspends maturing

a fault for the Oxygen Sensor Monitor if an of the fol-
lowing are present:

• Oxygen Sensor Heater Monitor, Priority 1

• Misfire Monitor, Priority 2

OXYGEN SENSOR HEATER MONITOR (NGC)

DESCRIPTION—If 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.

EMISSIONS CONTROL

25 - 3

EMISSIONS CONTROL (Continued)

OXYGEN SENSOR HEATER MONITOR (SBEC)

DESCRIPTION—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.

The voltage readings taken from the O2S are very

temperature sensitive. The readings are not accurate
below 300°C. 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.

OPERATION—The 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 Conditions—The following conditions

must be met for the PCM to run the oxygen sensor
heater test:

• Engine run time of at least 5.1 minutes

• Key OFF power down

• Battery voltage of at least 10 volts

• Sufficient Oxygen Sensor cool down
Pending Conditions—There 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.

Suspend—There 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 CONTROL

EMISSIONS CONTROL (Continued)

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