Diffe JEEP GRAND CHEROKEE 2002 WJ / 2.G Workshop Manual

(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
Generic Scan
Tool P-CodeDRB Scan Tool Display Brief Description of DTC
P1291 (M) No Temperature Rise Seen From
Intake Air HeatersProblem detected in intake manifold air heating system.
P1292 CNG Pressure Sensor Voltage Too
HighCompressed natural gas pressure sensor reading above
acceptable voltage.
P1293 CNG Pressure Sensor Voltage Too
LowCompressed natural gas pressure sensor reading below
acceptable voltage.
P1294 (M) Target Idle Not Reached Target RPM not achieved during drive idle condition.
Possible vacuum leak or IAC (AIS) lost steps.
P1295 (M) No 5 Volts to TP Sensor Loss of a 5 volt feed to the Throttle Position Sensor has
been detected.
P1295 (M) Accelerator Position Sensor (APPS)
Supply Voltage Too LowAPPS supply voltage input below the minimum
acceptable voltage.
P1296 No 5 Volts to MAP Sensor Loss of a 5 volt feed to the MAP Sensor has been
detected.
P1297 (M) No Change in MAP From Start To
RunNo difference is recognized between the MAP reading at
engine idle and the stored barometric pressure reading.
P1298 Lean Operation at Wide Open
ThrottleA prolonged lean condition is detected during Wide Open
Throttle
P1299 Vacuum Leak Found (IAC Fully
Seated)MAP Sensor signal does not correlate to Throttle Position
Sensor signal. Possible vacuum leak.
P1388 Auto Shutdown Relay Control Circuit An open or shorted condition detected in the ASD or CNG
shutoff relay control ckt.
P1388 Auto Shutdown Relay Control Circuit An open or shorted condition detected in the auto
shutdown relay circuit.
P1389 No ASD Relay Output Voltage At
PCMNo Z1 or Z2 voltage sensed when the auto shutdown
relay is energized.
P1389 (M) No ASD Relay Output Voltage at
PCMAn open condition detected In the ASD relay output
circuit.
P1390 Timing Belt Skipped 1 Tooth or More Relationship between Cam and Crank signals not correct
P1391 (M) Intermittent Loss of CMP or CKP Loss of the Cam Position Sensor or Crank Position
sensor has occurred. For PL 2.0L
P1398 (M) Mis-Fire Adaptive Numerator at Limit PCM is unable to learn the Crank Sensor's signal in
preparation for Misfire Diagnostics. Probable defective
Crank Sensor
P1399 Wait To Start Lamp Cicuit An open or shorted condition detected in the Wait to Start
Lamp circuit.
P1403 No 5V to EGR Sensor Loss of 5v feed to the EGR position sensor.
P01475 Aux 5 Volt Supply Voltage High Sensor supply voltage for ECM sensors is too high.
P1476 Too Little Secondary Air Insufficient flow of secondary air injection detected during
aspirator test (was P0411)
P1477 Too Much Secondary Air Excessive flow of secondary air injection detected during
aspirator test (was P0411).
25 - 12 EMISSIONS CONTROLWJ
EMISSIONS CONTROL (Continued)

(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
Generic Scan
Tool P-CodeDRB Scan Tool Display Brief Description of DTC
P1756 (M) GOV Press Not Equal to Target @
15-20 PSIThe requested pressure and the actual pressure are not
within a tolerance band for the Governor Control System
which is used to regulate governor pressure to control
shifts for 1st, 2nd, and 3rd gear. (Mid Pressure
Malfunction)
P1756 (M) Governor Pressure Not Equal to
Target @ 15-20 PSIGovernor sensor input not between 10 and 25 psi when
requested (4-speed auto. trans. only).
P1757 GOV Press Not Equal to Target @
15-20 PSIThe requested pressure and the actual pressure are not
within a tolerance band for the Governor Control System
which is used to regulate governor pressure to control
shifts for 1st, 2nd, and 3rd gear (Zero Pressure
Malfunction)
P1757 (M) Governor Pressure Above 3 PSI In
Gear With 0 MPHGovernor pressure greater than 3 psi when requested to
be 0 psi (4-speed auto. trans. only).
P1762 (M) Gov Press Sen Offset Volts Too Lo
or HighThe Governor Pressure Sensor input is greater than a
calibration limit or is less than a calibration limit for 3
consecutive park/neutral calibrations.
P1762 (M) Governor Press Sen Offset Volts Too
Low or HighSensor input greater or less than calibration for 3
consecutive Neutral/Park occurrences (4-speed auto.
trans. only).
P1763 Governor Pressure Sensor Volts Too
HiThe Governor Pressure Sensor input is above an
acceptable voltage level.
P1763 (M) Governor Pressure Sensor Volts Too
HIVoltage greater than 4.89 volts (4-speed auto. trans.
only).
P1764 (M) Governor Pressure Sensor Volts Too
LowThe Governor Pressure Sensor input is below an
acceptable voltage level.
P1764 (M) Governor Pressure Sensor Volts Too
LowVoltage less than .10 volts (4-speed auto. trans. only).
P1765 (M) Trans 12 Volt Supply Relay CTRL
CircuitAn 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
CircuitCurrent state of solenoid output port is different than
expected (4-speed auto. trans. only).
P1830 Clutch Override Relay Circuit Problem detected in clutch pedal switch override relay
circuit.
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).
25 - 16 EMISSIONS CONTROLWJ
EMISSIONS CONTROL (Continued)

DESCRIPTION - TASK MANAGER
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 referred to as the 'Task Manager'.
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 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:
²Misfire Monitor
²Fuel System Monitor
²Oxygen Sensor Monitor
²Oxygen Sensor Heater Monitor
²Catalyst Monitor
²Leak 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 300É to 350ÉC (572É to 662ÉF), 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:
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. 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) shorted to volt-
age 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 oper-
ating temperature 300É to 350ÉC (572 É to 662ÉF), 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 voltage readings taken from the O2S sensor
are very temperature sensitive. The readings are not
accurate below 300ÉC. 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 pri-
mary functions: it must detect a leak in the evapora-
WJEMISSIONS CONTROL 25 - 17
EMISSIONS CONTROL (Continued)

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 effi-
ciency 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-
verter. The PCM calculates the A/F mixture from the
output of the O2S. A low voltage indicates high oxy-
gen 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 will be illu-
minated.
DESCRIPTION - TRIP DEFINITION
The term ªTripº has different meanings depending
on what the circumstances are. If the MIL (Malfunc-
tion 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, itdepends on what type of DTC is set to know what a
ªTripº is.
For the Fuel Monitor or Mis-Fire Monitor (contin-
uous monitor), the vehicle must be operated in the
ªSimilar Condition Windowº 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:
²Oxygen Sensor
²Catalyst Monitor
²Purge Flow Monitor
²Leak Detection Pump Monitor (if equipped)
²EGR Monitor (if equipped)
²Oxygen 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 160ÉF and
has risen by at least 40ÉF since the engine has been
started.
DESCRIPTION - COMPONENT MONITORS
There are several components that will affect vehi-
cle emissions if they malfunction. If one of these com-
ponents 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
WJEMISSIONS CONTROL 25 - 19
EMISSIONS CONTROL (Continued)

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 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:
²Test Sequence
²MIL Illumination
²Diagnostic Trouble Codes (DTCs)
²Trip Indicator
²Freeze Frame Data Storage
²Similar 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).
²Pending
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 monitorspendingresolu-
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.
²Conflict
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 thiscon-
flictis 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 inprogress, 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.
²Suspend
Occasionally the Task Manager may not allow a two
trip fault to mature. The Task Manager willsus-
pendthe 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 MIL 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
²Priority 0 ÐNon-emissions related trouble codes
²Priority 1 Ð One trip failure of a two trip fault
for non-fuel system and non-misfire.
²Priority 2 Ð One trip failure of a two trip fault
for fuel system (rich/lean) or misfire.
²Priority3ÐTwotrip failure for a non-fuel sys-
tem and non-misfire or matured one trip comprehen-
sive component fault.
²Priority4ÐTwotrip failure or matured fault
for fuel system (rich/lean) and misfire or one trip cat-
alyst damaging misfire.
WJEMISSIONS CONTROL 25 - 21
EMISSIONS CONTROL (Continued)

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  375
RPM and load is within  10% 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
TheTripis 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:
²Specific Good Trip
²Fuel System Good Trip
²Misfire Good Trip
²Alternate Good Trip (appears as a Global Good
Trip on DRB III)
²Comprehensive Components
²Major Monitor
²Warm-Up CyclesSpecific Good Trip
The term Good Trip has different meanings
depending on the circumstances:
²If 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.
²If 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.
²If 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.
²If 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:
²Engine in closed loop
²Operating in Similar Conditions Window
²Short Term multiplied by Long Term less than
threshold
²Less 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:
²Operating in Similar Condition Window
²1000 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:
²Engine coolant temperature must start below
and rise above 160É F
²Engine coolant temperature must rise by 40É F
²No further faults occur
25 - 22 EMISSIONS CONTROLWJ
EMISSIONS CONTROL (Continued)

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
²Fuel System Similar Conditions WindowÐ
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'.
²Absolute MAP When Fuel Sys FailÐ The
stored MAP reading at the time of failure. Informs
the user at what engine load the failure occurred.
²Absolute MAPÐ A live reading of engine load
to aid the user in accessing the Similar Conditions
Window.
²RPM When Fuel Sys FailÐ The stored RPM
reading at the time of failure. Informs the user at
what engine RPM the failure occurred.
²Engine RPMÐ A live reading of engine RPM
to aid the user in accessing the Similar Conditions
Window.
²Adaptive Memory FactorÐ The PCM utilizes
both Short Term Compensation and Long Term Adap-
tive to calculate the Adaptive Memory Factor for
total fuel correction.
²Upstream O2S VoltsÐ A live reading of the
Oxygen Sensor to indicate its performance. For
example, stuck lean, stuck rich, etc.
²SCW Time in Window (Similar Conditions
Window Time in Window)Ð A timer used by thePCM 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.
²Fuel System Good Trip CounterÐATrip
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
must stay below that threshold for a calibrated
amount of time.
²Test Done This TripÐ Indicates that the
monitor has already been run and completed during
the current trip.
MISFIRE
²Same Misfire Warm-Up StateÐ Indicates if
the misfire occurred when the engine was warmed up
(above 160É F).
²In Similar Misfire WindowÐ 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'.
²Absolute MAP When Misfire OccurredÐ
The stored MAP reading at the time of failure.
Informs the user at what engine load the failure
occurred.
²Absolute MAPÐ A live reading of engine load
to aid the user in accessing the Similar Conditions
Window.
²RPM When Misfire OccurredÐ The stored
RPM reading at the time of failure. Informs the user
at what engine RPM the failure occurred.
²Engine RPMÐ A live reading of engine RPM
to aid the user in accessing the Similar Conditions
Window.
²Adaptive Memory FactorÐ The PCM utilizes
both Short Term Compensation and Long Term Adap-
tive to calculate the Adaptive Memory Factor for
total fuel correction.
²200 Rev CounterÐ Counts 0±100 720 degree
cycles.
²SCW Cat 200 Rev CounterÐ Counts when in
similar conditions.
²SCW FTP 1000 Rev CounterÐ Counts 0±4
when in similar conditions.
²Misfire Good Trip CounterÐ Counts up to
three to turn OFF the MIL.
²Misfire DataÐ Data collected during test.
²Test Done This TripÐ Indicates YES when the
test is done.
WJEMISSIONS CONTROL 25 - 23
EMISSIONS CONTROL (Continued)

²No engine stall during test.
NOTE: IF BATTERY VOLTAGE DROPS BELOW 10
VOLTS FOR MORE THAN 5 SECONDS DURING
ENGINE CRANKING, THE EVAP LEAK DETECTION
TEST WILL NOT RUN.
NOTE: THE FOLLOWING VALUES ARE APPROXI-
MATE AND VEHICLE SPECIFIC. USE THE VALUES
SEEN IN PRE TEST/MONITOR TEST SCREEN ON
THE DRB IIIT. SEE TSB 25-02-98 FOR MORE
DETAIL.
A DTC will not be set if a one-trip fault is set or if
the MIL is illuminated for any of the following:
²Purge Solenoid Electrical Fault
²All TPS Faults
²All Engine Controller Self Test Faults
²LDP Pressure Switch Fault
²All Cam and/or Crank Sensor Fault
²EGR Solenoid Electrical Fault
²All MAP Sensor Faults
²All Injector Faults
²Ambient/Battery Temperature Sensor Electrical
Faults²Baro Out of Range
²Vehicle Speed Faults
²All Coolant Sensor Faults
²LDP Solenoid Circuit
NOTE: IF BATTERY TEMPERATURE IS NOT WITHIN
RANGE, OR IF THE ENGINE COOLANT TEMPERA-
TURE IS NOT WITHIN A SPECIFIED RANGE OF THE
BATTERY TEMPERATURE, THE PCM WILL NOT
RUN TESTS FOR DTC P1494, P1486, P0442, P0455
AND P0441. THESE TEMPERATURE CALIBRATIONS
MAY BE DIFFERENT BETWEEN MODELS.
SECTION 1 - P1495 Leak Detection Pump
Solenoid Circuit-When the ignition key is turned
to9ON9, the LDP diaphragm should be in the down
position and the LDP reed switch should be closed. If
the EVAP system has residual pressure, the LDP dia-
phragm may be up. This could result in the LDP reed
switch being open when the key is turned to9ON9
and a P1494 fault could be set because the PCM is
expecting the reed switch to be closed.
After the key is turned9ON9, the PCM immedi-
ately tests the LDP solenoid circuit for electrical
faults. If a fault is detected, DTC P1495 will set, the
Fig. 15 DIAPHRAGM DOWNWARD MOVEMENT
1 - Diaphragm
2 - Inlet Check Valve (Closed)
3 - Vent Valve (Closed)
4 - From Air Filter
5 - To Canister
6 - Outlet Check Valve (Open)
7 - Engine Vacuum (Closed)EVAP LDP TEST SEQUENCE
1 - IGNITION SWITCH
2 - LDP DIAPHRAM
3 - LDP SWITCH
4 - LDP SOLENOID
5 - SECTION 1
6 - SECTION 2
7 - SECTION 3
8 - SECTION 4
9 - SECTION 5
10 - 3 TEST CYCLES TO TEST FOR BLOCKAGE
11- RAPID PUMP CYCLING FOR 70 CYCLES
WJEVAPORATIVE EMISSIONS 25 - 33
LEAK DETECTION PUMP (Continued)