Dodge Emissions Control Service Manual

DR EMISSIONS CONTROL 25 - 1

EMISSIONS CONTROL

TABLE OF CONTENTS

page page

EMISSIONS CONTROL

DESCRIPTION

DESCRIPTION - STATE DISPLAY TEST

MODE ...............................1

DESCRIPTION - CIRCUIT ACTUATION TEST

MODE ...............................1

DESCRIPTION - DIAGNOSTIC TROUBLE

CODES ..............................1

DESCRIPTION - TASK MANAGER ..........1

EMISSIONS CONTROL

DESCRIPTION

DESCRIPTION - STATE DISPLAY TEST MODE

The switch inputs to the Powertrain Control Mod­ule (PCM) have two recognized states; HIGH and
LOW. For this reason, the PCM cannot recognize the
difference between a selected switch position versus
an open circuit, a short circuit, or a defective switch.
If the State Display screen shows the change from
HIGH to LOW or LOW to HIGH, assume the entire
switch circuit to the PCM functions properly. Connect
the DRB scan tool to the data link connector and
access the state display screen. Then access either
State Display Inputs and Outputs or State Display
Sensors.

DESCRIPTION - CIRCUIT ACTUATION TEST
MODE

The Circuit Actuation Test Mode checks for proper
operation of output circuits or devices the Powertrain
Control Module (PCM) may not internally recognize.
The PCM attempts to activate these outputs and
allow an observer to verify proper operation. Most of
the tests provide an audible or visual indication of
device operation (click of relay contacts, fuel spray,
etc.). Except for intermittent conditions, if a device
functions properly during testing, assume the device,
its associated wiring, and driver circuit work cor­rectly. Connect the DRB scan tool to the data link
connector and access the Actuators screen.

DESCRIPTION - DIAGNOSTIC TROUBLE CODES

A Diagnostic Trouble Code (DTC) indicates the
PCM has recognized an abnormal condition in the
system.

DESCRIPTION - MONITORED SYSTEMS ....1

DESCRIPTION - TRIP DEFINITION .........4

DESCRIPTION - COMPONENT MONITORS . . 4

OPERATION

OPERATION ..........................4

OPERATION - TASK MANAGER ...........5

OPERATION - NON-MONITORED CIRCUITS . . 8

EVAPORATIVE EMISSIONS ................10

Remember that DTC’s are the results of a sys­tem or circuit failure, but do not directly iden­tify the failed component or components.

BULB CHECK

Each time the ignition key is turned to the ON
position, the malfunction indicator (check engine)
lamp on the instrument panel should illuminate for
approximately 2 seconds then go out. This is done for
a bulb check.

OBTAINING DTC’S USING DRB SCAN TOOL

(1) Obtain the applicable Powertrain Diagnostic
Manual.

(2) Obtain the DRB Scan Tool.

(3) Connect the DRB Scan Tool to the data link
(diagnostic) connector. This connector is located in
the passenger compartment; at the lower edge of
instrument panel; near the steering column.

(4) Turn the ignition switch on and access the
“Read Fault” screen.

(5) Record all the DTC’s and “freeze frame” infor­mation shown on the DRB scan tool.

(6) To erase DTC’s, use the “Erase Trouble Code”
data screen on the DRB scan tool. Do not erase any

DTC’s until problems have been investigated
and repairs have been performed.

DESCRIPTION - TASK MANAGER

The PCM is responsible for efficiently coordinating
the operation of all the emissions-related compo­nents. The PCM is also responsible for determining if
the diagnostic systems are operating properly. The
software designed to carry out these responsibilities
is call the ’Task Manager’.

DESCRIPTION - MONITORED SYSTEMS

There are new electronic circuit monitors that
check fuel, emission, engine and ignition perfor-

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EMISSIONS CONTROL (Continued)

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 prob­lem. They do indicate that there is an implied prob­lem 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 Lamp
(MIL) will be illuminated. These monitors generate
Diagnostic Trouble Codes that can be displayed with
the MIL or a scan tool.

The following is a list of the system monitors:

• Misfire Monitor

• Fuel System Monitor

• Oxygen Sensor Monitor

• Oxygen Sensor Heater Monitor

• Catalyst Monitor

• Leak Detection Pump Monitor (if equipped)

All these system monitors require two consecutive
trips with the malfunction present to set a fault.

Refer to the appropriate Powertrain Diagnos­tics Procedures manual for diagnostic proce­dures.

The following is an operation and description of
each system monitor :

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 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. The
information obtained by the sensor is used to calcu­late the fuel injector pulse width. This maintains 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 O2S is also the main sensing element for the
Catalyst and Fuel Monitors.

The O2S can fail in any or all of the following
manners:

• slow response rate

• reduced output voltage

• dynamic shift

• shorted 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 sen­sor 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. 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.

OXYGEN SENSOR HEATER MONITOR

If there is an oxygen sensor (O2S) shorted to volt­age DTC, as well as a O2S heater DTC, the O2S
fault MUST be repaired first. Before checking the
O2S fault, 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 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. The
information obtained by the sensor is used to calcu­late the fuel injector pulse width. This maintains 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 sensor
are very temperature sensitive. The readings are not
accurate below 300°C. Heating of the O2S sensor 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 sensor must be tested to ensure
that it is heating the sensor properly.

The O2S sensor circuit is monitored for a drop in
voltage. The sensor output is used to test the heater
by isolating the effect of the heater element on the
O2S sensor output voltage from the other effects.

LEAK DETECTION PUMP MONITOR (IF EQUIPPED)

The leak detection assembly incorporates two pri­mary functions: it must detect a leak in the evapora­tive system and seal the evaporative system so the
leak detection test can be run.

The primary components within the assembly are:
A three port solenoid that activates both of the func­tions listed above; a pump which contains a switch,
two check valves and a spring/diaphragm, a canister
vent valve (CVV) seal which contains a spring loaded
vent seal valve.

Immediately after a cold start, between predeter­mined temperature thresholds limits, the three port
solenoid is briefly energized. This initializes the

DR EMISSIONS CONTROL 25 - 3

EMISSIONS CONTROL (Continued)

pump by drawing air into the pump cavity and also
closes the vent seal. During non test conditions the
vent seal is held open by the pump diaphragm
assembly which pushes it open at the full travel posi­tion. The vent seal will remain closed while the
pump is cycling due to the reed switch triggering of
the three port solenoid that prevents the diaphragm
assembly from reaching full travel. After the brief
initialization period, the solenoid is de-energized
allowing atmospheric pressure to enter the pump
cavity, thus permitting the spring to drive the dia­phragm which forces air out of the pump cavity and
into the vent system. When the solenoid is energized
and de energized, the cycle is repeated creating flow
in typical diaphragm pump fashion. The pump is con­trolled in 2 modes:

Pump Mode: The pump is cycled at a fixed rate to
achieve a rapid pressure build in order to shorten the
overall test length.

Test Mode: The solenoid is energized with a fixed
duration pulse. Subsequent fixed pulses occur when
the diaphragm reaches the Switch closure point.

The spring in the pump is set so that the system
will achieve an equalized pressure of about 7.5” H20.
The cycle rate of pump strokes is quite rapid as the
system begins to pump up to this pressure. As the
pressure increases, the cycle rate starts to drop off. If
there is no leak in the system, the pump would even­tually stop pumping at the equalized pressure. If
there is a leak, it will continue to pump at a rate rep­resentative of the flow characteristic of the size of the
leak. From this information we can determine if the
leak is larger than the required detection limit (cur­rently set at .040” orifice by CARB). If a leak is
revealed during the leak test portion of the test, the
test is terminated at the end of the test mode and no
further system checks will be performed.

After passing the leak detection phase of the test,
system pressure is maintained by turning on the
LDP’s solenoid until the purge system is activated.
Purge activation in effect creates a leak. The cycle
rate is again interrogated and when it increases due
to the flow through the purge system, the leak check
portion of the diagnostic is complete.

The canister vent valve will unseal the system
after completion of the test sequence as the pump
diaphragm assembly moves to the full travel position.

Evaporative system functionality will be verified by
using the stricter evap purge flow monitor. At an
appropriate warm idle the LDP will be energized to
seal the canister vent. The purge flow will be clocked
up from some small value in an attempt to see a
shift in the 02 control system. If fuel vapor, indicated
by a shift in the 02 control, is present the test is
passed. If not, it is assumed that the purge system is

not functioning in some respect. The LDP is again
turned off and the test is ended.

MISFIRE MONITOR

Excessive engine misfire results in increased cata­lyst temperature and causes an increase in HC emis­sions. 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 crank­shaft 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 nitro­gen and carbon monoxide. The catalyst works best
when the Air Fuel (A/F) ratio is at or near the opti­mum of 14.7 to 1.

The PCM is programmed to maintain the optimum
air/fuel ratio of 14.7 to 1. This is done by making
short term corrections in the fuel injector pulse width
based on the O2S sensor 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 fuel-air ratio with the O2S sensor (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 malfunction 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 nitro­gen and carbon monoxide.

Normal vehicle miles or engine misfire can cause a
catalyst to decay. 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 sensor strategy is based on the fact that
as a catalyst deteriorates, its oxygen storage capacity
and its efficiency are both reduced. By monitoring
the oxygen 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 con-

25 - 4 EMISSIONS CONTROL DR

EMISSIONS CONTROL (Continued)

verter. 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 con­centration 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-to­one, indicating that no oxidation occurs in the device.

The system must be monitored so that when cata­lyst efficiency deteriorates and exhaust emissions
increase to over the legal limit, the MIL will be illu­minated.

DESCRIPTION - TRIP DEFINITION

The term “Trip” has different meanings depending
on what the circumstances are. If the MIL (Malfunc­tion Indicator Lamp) is OFF, a Trip is defined as
when the Oxygen Sensor Monitor and the Catalyst
Monitor have been completed in the same drive cycle.

When any Emission DTC is set, the MIL on the
dash is turned ON. When the MIL is ON, it takes 3
good trips to turn the MIL OFF. In this case, it
depends on what type of DTC is set to know what a
“Trip” is.

For the Fuel Monitor or Mis-Fire Monitor (contin­uous monitor), the vehicle must be operated in the
“Similar Condition Window” for a specified amount of
time to be considered a Good Trip.

If a Non-Contiuous OBDII Monitor fails twice in a
row and turns ON the MIL, re-running that monitor
which previously failed, on the next start-up and
passing the monitor, is considered to be a Good Trip.
These will include the following:

• Oxygen Sensor

• Catalyst Monitor

• Purge Flow Monitor

• Leak Detection Pump Monitor (if equipped)

• EGR Monitor (if equipped)

• Oxygen Sensor Heater Monitor

If any other Emission DTC is set (not an OBDII
Monitor), a Good Trip is considered to be when the
Oxygen Sensor Monitor and Catalyst Monitor have
been completed; or 2 Minutes of engine run time if
the Oxygen Sensor Monitor or Catalyst Monitor have
been stopped from running.

It can take up to 2 Failures in a row to turn on the
MIL. After the MIL is ON, it takes 3 Good Trips to
turn the MIL OFF. After the MIL is OFF, the PCM
will self-erase the DTC after 40 Warm-up cycles. A
Warm-up cycle is counted when the ECT (Engine
Coolant Temperature Sensor) has crossed 160°F and
has risen by at least 40°F since the engine has been
started.

DESCRIPTION - COMPONENT MONITORS

There are several components that will affect vehi­cle emissions if they malfunction. If one of these com­ponents malfunctions the Malfunction Indicator
Lamp (MIL) 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 if
the TPS indicates a small throttle opening.

All open/short circuit checks, or any component
that has an associated limp-in, will set a fault after 1
trip with the malfunction present. Components with­out an associated limp-in will take two trips to illu­minate the MIL.

OPERATION

OPERATION

The Powertrain Control Module (PCM) monitors
many different circuits in the fuel injection, ignition,
emission and engine systems. If the PCM senses a
problem with a monitored circuit often enough to
indicate an actual problem, it stores a Diagnostic
Trouble Code (DTC) in the PCM’s memory. If the

DR EMISSIONS CONTROL 25 - 5

EMISSIONS CONTROL (Continued)

problem is repaired or ceases to exist, the PCM can­cels the code after 40 warm-up cycles. Diagnostic
trouble codes that affect vehicle emissions illuminate
the Malfunction Indicator Lamp (MIL). The MIL is
displayed as an engine icon (graphic) on the instru­ment panel. Refer to Malfunction Indicator Lamp in
this section.

Certain criteria must be met before the PCM
stores a DTC in memory. The criteria may be a spe­cific range of engine RPM, engine temperature,
and/or input voltage to the PCM.

The PCM might not store a DTC for a monitored
circuit even though a malfunction has occurred. This
may happen because one of the DTC criteria for the
circuit has not been met. For example, assume the
diagnostic trouble code criteria requires the PCM to
monitor the circuit only when the engine operates
between 750 and 2000 RPM. Suppose the sensor’s
output circuit shorts to ground when engine operates
above 2400 RPM (resulting in 0 volt input to the
PCM). Because the condition happens at an engine
speed above the maximum threshold (2000 rpm), the
PCM will not store a DTC.

There are several operating conditions for which
the PCM monitors and sets DTC’s. Refer to Moni­tored Systems, Components, and Non-Monitored Cir­cuits in this section.

Technicians must retrieve stored DTC’s by connect­ing the DRB scan tool (or an equivalent scan tool) to
the 16–way data link connector. The connector is
located on the bottom edge of the instrument panel
near the steering column (Fig. 1).

NOTE: Various diagnostic procedures may actually
cause a diagnostic monitor to set a DTC. For
instance, pulling a spark plug wire to perform a
spark test may set the misfire code. When a repair
is completed and verified, connect the DRB scan
tool to the 16–way data link connector to erase all
DTC’s and extinguish the MIL.

OPERATION - TASK MANAGER

The Task Manager determines which tests happen
when and which functions occur when. Many of the
diagnostic steps required by OBD II must be per­formed under specific operating conditions. The Task
Manager software organizes and prioritizes the diag­nostic procedures. The job of the Task Manager is to
determine if conditions are appropriate for tests to be
run, monitor the parameters for a trip for each test,
and record the results of the test. Following are the
responsibilities of the Task Manager software:

• Test Sequence

• MIL Illumination

• Diagnostic Trouble Codes (DTCs)

• Trip Indicator

Fig. 1 DATA LINK CONNECTOR LOCATION -

TYPICAL

1 - 16-WAY DATA LINK CONNECTOR

• Freeze Frame Data Storage

• Similar Conditions Window

Test Sequence

In many instances, emissions systems must fail
diagnostic tests more than once before the PCM illu­minates the MIL. These tests are know as ’two trip
monitors.’ Other tests that turn the MIL lamp on
after a single failure are known as ’one trip moni­tors.’ A trip is defined as ’start the vehicle and oper­ate it to meet the criteria necessary to run the given
monitor.’

Many of the diagnostic tests must be performed
under certain operating conditions. However, there
are times when tests cannot be run because another
test is in progress (conflict), another test has failed
(pending) or the Task Manager has set a fault that
may cause a failure of the test (suspend).

• Pending
Under some situations the Task Manager will not
run a monitor if the MIL is illuminated and a fault is
stored from another monitor. In these situations, the
Task Manager postpones monitors pending resolu­tion of the original fault. The Task Manager does not
run the test until the problem is remedied.
For example, when the MIL is illuminated for an
Oxygen Sensor fault, the Task Manager does not run
the Catalyst Monitor until the Oxygen Sensor fault is
remedied. Since the Catalyst Monitor is based on sig­nals from the Oxygen Sensor, running the test would
produce inaccurate results.

• Conflict
There are situations when the Task Manager does
not run a test if another monitor is in progress. In

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EMISSIONS CONTROL (Continued)

these situations, the effects of another monitor run­ning could result in an erroneous failure. If this con-
flict is present, the monitor is not run until the
conflicting condition passes. Most likely the monitor
will run later after the conflicting monitor has
passed.
For example, if the Fuel System Monitor is in
progress, the Task Manager does not run the EGR
Monitor. Since both tests monitor changes in air/fuel
ratio and adaptive fuel compensation, the monitors
will conflict with each other.

• Suspend
Occasionally the Task Manager may not allow a two
trip fault to mature. The Task Manager will sus-
pend the maturing of a fault if a condition exists
that may induce an erroneous failure. This prevents
illuminating the MIL for the wrong fault and allows
more precis diagnosis.
For example, if the PCM is storing a one trip fault
for the Oxygen Sensor and the EGR monitor, the
Task Manager may still run the EGR Monitor but
will suspend the results until the Oxygen Sensor
Monitor either passes or fails. At that point the Task
Manager can determine if the EGR system is actu­ally failing or if an Oxygen Sensor is failing.

MIL Illumination

The PCM Task Manager carries out the illumina­tion of the MIL. The Task Manager triggers MIL illu­mination upon test failure, depending on monitor
failure criteria.

The Task Manager Screen shows both a Requested
MIL state and an Actual MIL state. When the MIL is
illuminated upon completion of a test for a third trip,
the Requested MIL state changes to OFF. However,
the MIL remains illuminated until the next key
cycle. (On some vehicles, the MIL will actually turn
OFF during the third key cycle) During the key cycle
for the third good trip, the Requested MIL state is
OFF, while the Actual MILL state is ON. After the
next key cycle, the MIL is not illuminated and both
MIL states read OFF.

Diagnostic Trouble Codes (DTCs)

With OBD II, different DTC faults have different
priorities according to regulations. As a result, the
priorities determine MIL illumination and DTC era­sure. DTCs are entered according to individual prior­ity. DTCs with a higher priority overwrite lower
priority DTCs.

Priorities

• Priority 0 —Non-emissions related trouble codes

• Priority 1 — One trip failure of a two trip fault

for non-fuel system and non-misfire.

• Priority 2 — One trip failure of a two trip fault

for fuel system (rich/lean) or misfire.

• Priority3—Twotrip failure for a non-fuel sys­tem and non-misfire or matured one trip comprehen­sive component fault.

• Priority4—Twotrip failure or matured fault
for fuel system (rich/lean) and misfire or one trip cat­alyst damaging misfire.

Non-emissions related failures have no priority.
One trip failures of two trip faults have low priority.
Two trip failures or matured faults have higher pri­ority. One and two trip failures of fuel system and
misfire monitor take precedence over non-fuel system
and non-misfire failures.

DTC Self Erasure

With one trip components or systems, the MIL is
illuminated upon test failure and DTCs are stored.

Two trip monitors are components requiring failure
in two consecutive trips for MIL illumination. Upon
failure of the first test, the Task Manager enters a
maturing code. If the component fails the test for a
second time the code matures and a DTC is set.

After three good trips the MIL is extinguished and
the Task Manager automatically switches the trip
counter to a warm-up cycle counter. DTCs are auto­matically erased following 40 warm-up cycles if the
component does not fail again.

For misfire and fuel system monitors, the compo­nent must pass the test under a Similar Conditions
Window in order to record a good trip. A Similar Con­ditions Window is when engine RPM is within ±375
RPM and load is within ±10% of when the fault
occurred.

NOTE: It is important to understand that a compo­nent does not have to fail under a similar window of
operation to mature. It must pass the test under a
Similar Conditions Window when it failed to record
a Good Trip for DTC erasure for misfire and fuel
system monitors.

DTCs can be erased anytime with a DRB III. Eras­ing the DTC with the DRB III erases all OBD II
information. The DRB III automatically displays a
warning that erasing the DTC will also erase all
OBD II monitor data. This includes all counter infor­mation for warm-up cycles, trips and Freeze Frame.

Trip Indicator

The Trip is essential for running monitors and
extinguishing the MIL. In OBD II terms, a trip is a
set of vehicle operating conditions that must be met
for a specific monitor to run. All trips begin with a
key cycle.

Good Trip

The Good Trip counters are as follows:

DR EMISSIONS CONTROL 25 - 7

EMISSIONS CONTROL (Continued)

• Specific Good Trip

• Fuel System Good Trip

• Misfire Good Trip

• Alternate Good Trip (appears as a Global Good

Trip on DRB III)

• Comprehensive Components

• Major Monitor

• Warm-Up Cycles

Specific Good Trip

The term Good Trip has different meanings

depending on the circumstances:

• If the MIL is OFF, a trip is defined as when the
Oxygen Sensor Monitor and the Catalyst Monitor
have been completed in the same drive cycle.

• If the MIL is ON and a DTC was set by the Fuel
Monitor or Misfire Monitor (both continuous moni­tors), the vehicle must be operated in the Similar
Condition Window for a specified amount of time.

• If the MIL is ON and a DTC was set by a Task
Manager commanded once-per-trip monitor (such as
the Oxygen Sensor Monitor, Catalyst Monitor, Purge
Flow Monitor, Leak Detection Pump Monitor, EGR
Monitor or Oxygen Sensor Heater Monitor), a good
trip is when the monitor is passed on the next start­up.

• If the MIL is ON and any other emissions DTC
was set (not an OBD II monitor), a good trip occurs
when the Oxygen Sensor Monitor and Catalyst Mon­itor have been completed, or two minutes of engine
run time if the Oxygen Sensor Monitor and Catalyst
Monitor have been stopped from running.

Fuel System Good Trip

To count a good trip (three required) and turn off

the MIL, the following conditions must occur:

• Engine in closed loop

• Operating in Similar Conditions Window

• Short Term multiplied by Long Term less than

threshold

• Less than threshold for a predetermined time

If all of the previous criteria are met, the PCM will
count a good trip (three required) and turn off the
MIL.

Misfire Good Trip

If the following conditions are met the PCM will
count one good trip (three required) in order to turn
off the MIL:

• Operating in Similar Condition Window

• 1000 engine revolutions with no misfire

Warm-Up Cycles

Once the MIL has been extinguished by the Good
Trip Counter, the PCM automatically switches to a
Warm-Up Cycle Counter that can be viewed on the
DRB III. Warm-Up Cycles are used to erase DTCs
and Freeze Frames. Forty Warm-Up cycles must
occur in order for the PCM to self-erase a DTC and

Freeze Frame. A Warm-Up Cycle is defined as fol­lows:

• Engine coolant temperature must start below

and rise above 160° F

• Engine coolant temperature must rise by 40° F

• No further faults occur

Freeze Frame Data Storage

Once a failure occurs, the Task Manager records
several engine operating conditions and stores it in a
Freeze Frame. The Freeze Frame is considered one
frame of information taken by an on-board data
recorder. When a fault occurs, the PCM stores the
input data from various sensors so that technicians
can determine under what vehicle operating condi­tions the failure occurred.

The data stored in Freeze Frame is usually
recorded when a system fails the first time for two
trip faults. Freeze Frame data will only be overwrit­ten by a different fault with a higher priority.

CAUTION: Erasing DTCs, either with the DRB III or
by disconnecting the battery, also clears all Freeze
Frame data.

Similar Conditions Window

The Similar Conditions Window displays informa­tion about engine operation during a monitor. Abso­lute MAP (engine load) and Engine RPM are stored
in this window when a failure occurs. There are two
different Similar conditions Windows: Fuel System
and Misfire.

FUEL SYSTEM

• Fuel System Similar Conditions Window —
An indicator that ’Absolute MAP When Fuel Sys Fail’
and ’RPM When Fuel Sys Failed’ are all in the same
range when the failure occurred. Indicated by switch­ing from ’NO’ to ’YES’.

• Absolute MAP When Fuel Sys Fail — The
stored MAP reading at the time of failure. Informs
the user at what engine load the failure occurred.

• Absolute MAP — A live reading of engine load
to aid the user in accessing the Similar Conditions
Window.

• RPM When Fuel Sys Fail — The stored RPM
reading at the time of failure. Informs the user at
what engine RPM the failure occurred.

• Engine RPM — A live reading of engine RPM
to aid the user in accessing the Similar Conditions
Window.

• Adaptive Memory Factor — The PCM utilizes
both Short Term Compensation and Long Term Adap­tive to calculate the Adaptive Memory Factor for
total fuel correction.

25 - 8 EMISSIONS CONTROL DR

EMISSIONS CONTROL (Continued)

• Upstream O2S Volts — A live reading of the
Oxygen Sensor to indicate its performance. For
example, stuck lean, stuck rich, etc.

• SCW Time in Window (Similar Conditions
Window Time in Window) — A timer used by the

PCM that indicates that, after all Similar Conditions
have been met, if there has been enough good engine
running time in the SCW without failure detected.
This timer is used to increment a Good Trip.

• Fuel System Good Trip Counter —ATrip
Counter used to turn OFF the MIL for Fuel System
DTCs. To increment a Fuel System Good Trip, the
engine must be in the Similar Conditions Window,
Adaptive Memory Factor must be less than cali­brated threshold and the Adaptive Memory Factor
must stay below that threshold for a calibrated
amount of time.

• Test Done This Trip — Indicates that the
monitor has already been run and completed during
the current trip.

MISFIRE

• Same Misfire Warm-Up State — Indicates if
the misfire occurred when the engine was warmed up
(above 160° F).

• In Similar Misfire Window — An indicator
that ’Absolute MAP When Misfire Occurred’ and
’RPM When Misfire Occurred’ are all in the same
range when the failure occurred. Indicated by switch­ing from ’NO’ to ’YES’.

• Absolute MAP When Misfire Occurred —
The stored MAP reading at the time of failure.
Informs the user at what engine load the failure
occurred.

• Absolute MAP — A live reading of engine load
to aid the user in accessing the Similar Conditions
Window.

• RPM When Misfire Occurred — The stored
RPM reading at the time of failure. Informs the user
at what engine RPM the failure occurred.

• Engine RPM — A live reading of engine RPM
to aid the user in accessing the Similar Conditions
Window.

• Adaptive Memory Factor — The PCM utilizes
both Short Term Compensation and Long Term Adap­tive to calculate the Adaptive Memory Factor for
total fuel correction.

• 200 Rev Counter — Counts 0–100 720 degree
cycles.

• SCW Cat 200 Rev Counter — Counts when in
similar conditions.

• SCW FTP 1000 Rev Counter — Counts 0–4
when in similar conditions.

• Misfire Good Trip Counter — Counts up to
three to turn OFF the MIL.

• Misfire Data— Data collected during test.

• Test Done This Trip— Indicates YES when the

test is done.

OPERATION - NON-MONITORED CIRCUITS

The PCM does not monitor the following circuits,
systems and conditions that could have malfunctions
causing driveability problems. The PCM might not
store diagnostic trouble codes for these conditions.
However, problems with these systems may cause the
PCM to store diagnostic trouble codes for other sys­tems or components. EXAMPLE: a fuel pressure
problem will not register a fault directly, but could
cause a rich/lean condition or misfire. This could
cause the PCM to store an oxygen sensor or misfire
diagnostic trouble code

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 or fuel system 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.

CYLINDER COMPRESSION

The PCM cannot detect uneven, low, or high engine
cylinder compression.

EXHAUST SYSTEM

The PCM cannot detect a plugged, restricted or
leaking exhaust system, although it may set a fuel
system 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.