Dodge Durango (DN). Manual — part 208
(M)
Malfunction Indicator Lamp (MIL) illuminated during engine operation if this DTC was
recorded (depending if required by CARB and/or EPA). MIL is displayed as an engine icon on
instrument panel.
(G)
Generator lamp illuminated
P1764 (M)
Governor Pressure Sensor Volts Too
Low
Voltage less than.10 volts (4-speed auto. trans. only).
P1765 (M)
Trans 12 Volt Supply Relay CTRL
Circuit
An open or shorted condition is detected in the
Transmission Relay control circuit. This relay supplies
power to the TCC
P1765 (M)
Trans 12 Volt Supply Relay Ctrl
Circuit
Current state of solenoid output port is different than
expected (4-speed auto. trans. only).
P1899 (M)
P/N Switch Stuck in Park or in Gear
Incorrect input state detected for the Park/Neutral switch.
P1899 (M)
P/N Switch Stuck in Park or in Gear
Incorrect input state detected for the Park/Neutral switch
(3 or 4-speed auto. trans. only).
TASK MANAGER—GASOLINE POWERED
ENGINES ONLY
DESCRIPTION
The PCM is responsible for efficiently coordinating
the operation of all the emissions-related compo-
nents. 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’.
OPERATION
The Task Manager determines which tests happen
when and which functions occur when. Many of the
diagnostic steps required by OBD II must be per-
formed under specific operating conditions. The Task
Manager software organizes and prioritizes the diag-
nostic 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
• Freeze Frame Data Storage
• Similar Conditions Window
Test Sequence
In many instances, emissions systems must fail
diagnostic tests more than once before the PCM illu-
minates 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 moni-
tors.’ A trip is defined as ’start the vehicle and oper-
ate 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 resolu-
tion 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 sig-
nals 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
these situations, the effects of another monitor run-
ning 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-
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EMISSION CONTROL SYSTEMS
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DESCRIPTION AND OPERATION (Continued)
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 actu-
ally failing or if an Oxygen Sensor is failing.
MIL Illumination
The PCM Task Manager carries out the illumina-
tion of the MIL. The Task Manager triggers MIL illu-
mination 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 era-
sure. DTCs are entered according to individual prior-
ity. 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.
• Priority 3 — Two trip failure for a non-fuel sys-
tem and non-misfire or matured one trip comprehen-
sive component fault.
• Priority 4 — Two trip failure or matured fault
for fuel system (rich/lean) and misfire or one trip cat-
alyst 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 pri-
ority. 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 auto-
matically erased following 40 warm-up cycles if the
component does not fail again.
For misfire and fuel system monitors, the compo-
nent must pass the test under a Similar Conditions
Window in order to record a good trip. A Similar Con-
ditions Window is when engine RPM is within
6375
RPM and load is within
610% of when the fault
occurred.
NOTE: It is important to understand that a compo-
nent 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. Eras-
ing 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 infor-
mation 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:
• 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.
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EMISSION CONTROL SYSTEMS
25 - 17
DESCRIPTION AND OPERATION (Continued)
• If the MIL is ON and a DTC was set by the Fuel
Monitor or Misfire Monitor (both continuous moni-
tors), 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 start-
up.
• 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 Mon-
itor 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 fol-
lows:
• 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 condi-
tions 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 overwrit-
ten 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 informa-
tion about engine operation during a monitor. Abso-
lute 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 switch-
ing 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 uti-
lizes both Short Term Compensation and Long Term
Adaptive to calculate the Adaptive Memory Factor
for total fuel correction.
• 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 — A Trip
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 cali-
brated threshold and the Adaptive Memory Factor
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EMISSION CONTROL SYSTEMS
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DESCRIPTION AND OPERATION (Continued)
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 switch-
ing 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 uti-
lizes 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.
MONITORED SYSTEMS
OPERATION
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 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 Diagnos-
tics Procedures manual for diagnostic proce-
dures.
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 oper-
ating temperature 300° to 350°C (572° to 662°F), the
sensor generates a voltage that is inversely propor-
tional to the amount of oxygen in the exhaust. The
information obtained by the sensor is used to calcu-
late 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 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. 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
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EMISSION CONTROL SYSTEMS
25 - 19
DESCRIPTION AND OPERATION (Continued)
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