ABS DODGE NEON 2000 Service Repair Manual

DETERMINING SHIM THICKNESS
Shim thickness need be determined only if any of
the following parts are replaced:
²Transaxle case
²Transfer shaft
²Transfer shaft gear
²Transfer shaft bearings
²Governor support retainer
²Transfer shaft bearing retainer
²Retainer snap ring
²Governor support
Refer to Bearing Adjustment Procedure in rear of
this section to determine proper shim thickness.
STIRRUP AND STRAP INSTALLATION
Once bearing shim selection has been adjusted,
install stirrup and strap assembly onto transfer gear.
NOTE: Once the stirrup assembly is positioned
onto the transfer gear, it is necessary to ªclockº the
stirrup against the flats of the transfer gear retain-
ing nut.
(1) Position the stirrup on the transfer gear.
(2) Position strap.
(3) Install retaining bolts into transfer gear. Fin-
ger±tighten bolts.
(4) Turn stirrup clockwise against the flats of the
transfer gear retaining nut.
(5) Tighten retaining bolts to 23 N´m (200 in. lbs.).(6) Bend tabs of strap up against ªflatsºof retain-
ing bolts.
ASSEMBLY
To install transfer shaft, reverse the above proce-
dure.
Fig. 155 Install Transfer Shaft Bearing Cup
1 ± PRESS
2 ± HANDLE C-4171
3 ± SPECIAL TOOL L-4520
4 ± TRANSFER SHAFT BEARING RETAINER
5 ± ªOº RING
Fig. 156 Tighten Transfer Shaft Gear Retaining Nut
to 271 N´m (200 ft. lbs.)
1 ± TRANSFER SHAFT GEAR
2 ± TORQUE WRENCH
3 ± SPECIAL TOOL L-4434 AND ADAPTER C-4658
Fig. 157 Checking Transfer Shaft End Play
1 ± SPECIAL TOOL L-4432 AND C-4658
2 ± TRANSFER SHAFT GEAR
3 ± STEEL BALL (USE GREASE TO HOLD IN PLACE)
4 ± DIAL INDICATOR
5 ± SCREW (2)
21 - 120 TRANSAXLEPL
DISASSEMBLY AND ASSEMBLY (Continued)

(1) Using a punch, bend tabs on strap flat against
output gear (Fig. 162).
(2) Remove bolts holding retaining strap to stirrup
(Fig. 163).(3) Remove strap from output gear and stirrup
(Fig. 164).
(4) Remove stirrup from output gear (Fig. 165)
(Fig. 166).
Fig. 162 Bend Strap Tabs Flat
1 ± RETAINING TABS
2 ± STRAP
Fig. 163 Remove Strap Bolts
1 ± RETAINING BOLTS
2 ± STIRRUP
3 ± STRAP
Fig. 164 Remove Strap From Stirrup and Gear
1 ± OUTPUT GEAR
2 ± STRAP
Fig. 165 Remove Stirrup From Gear
1 ± OUTPUT GEAR
2 ± STIRRUP
21 - 122 TRANSAXLEPL
DISASSEMBLY AND ASSEMBLY (Continued)

STIRRUP AND RETAINING STRAP
INSTALLATION
Once bearing turning torque and shim selection
has been adjusted, install stirrup and strap assembly
onto output gear.
NOTE: Once the stirrup assembly is positioned
onto the output gear, it is necessary to ªclockº the
stirrup against the flats of the output gear retaining
nut.
(1) Position the stirrup on the output gear.
(2) Position strap.
(3) Install retaining bolts into output gear. Finger±
tighten bolts.
(4) Turn stirrup clockwise against the flats of the
output gear retaining nut (Fig. 188).
(5) Tighten retaining bolts to 23 N´m (200 in. lbs.)
(Fig. 189).
(6) Bend tabs of strap up against ªflatsºof retain-
ing bolts.
Fig. 187 Checking Bearing Turning Torque
1 ± OUTPUT SHAFT GEAR
2 ± TORQUE WRENCHFig. 188 Turn Stirrup Clockwise Against Flats Of
Retaining Nut
1 ± TURN STIRRUP CLOCKWISE
2 ± STRAP
Fig. 189 Tighten Strap Retaining Nuts
1 ± STRAP
2 ± OUTPUT GEAR
3 ± STIRRUP
21 - 128 TRANSAXLEPL
DISASSEMBLY AND ASSEMBLY (Continued)

REMOVAL AND INSTALLATION
WHEEL COVER (LOCK-ON)
REMOVE
NOTE: When unthreading the wheel cover retaining
nuts (Fig. 12) from the wheel nuts it is recom-
mended that a hand wrench be used and not an
impact wrench. Use of an impact wrench could
result in damage to the lock-on wheel cover retain-
ing nuts.
(1) Un-thread the 5 nuts (Fig. 12) attaching the
wheel cover to the wheel nuts.
(2) Grasp the wheel cover and pull straight out-
ward from the wheel. This will remove the wheel
cover from the wheel.
INSTALL
(1) Align the valve notch in the wheel cover with
the valve stem on the wheel (Fig. 12). Align the
wheel cover retaining nuts with the externally
threaded wheel nuts.
(2) By hand, start to thread all 5 of the wheel
cover retaining nuts onto the externally threaded
wheel nuts.
NOTE: When tightening the wheel cover retaining
nuts it is recommended that a hand wrench be used
and not an impact wrench. Use of an impact wrenchcould result in damage to the lock-on wheel cover
retaining nuts.
(3) Tighten each of the wheel cover retaining nuts.
If the retaining nut ªjumpsº a thread (slips), which is
an override feature of the retaining nut, retighten
the retaining nut to a point just prior to this occur-
ring. To avoid rattling of the wheel cover be sure all
five retaining nuts are correctly tightened.
WHEEL COVER RETAINING NUT
If a retaining nut for the lock-on wheel cover is
damaged, it can be replaced as a separate component
of the wheel cover. Use the following procedure for
replacing a wheel cover retaining nut.
REMOVE
(1) If required, remove the wheel cover from the
wheel. Refer to Wheel Cover Lock-On in the Removal
And Installation Section in this group of the service
manual for the procedure.
NOTE: The retaining nut flange can not be forced
past the large retaining tab. When removing retain-
ing nut from wheel cover, the flange on the retain-
ing nut must be forced past the 2 small retaining
tabs on wheel cover.
(2) From the back side of the wheel cover, push
outward and tilt the retaining nut sideways forcing
the flange on the retaining nut past the 2 small
retaining tabs in the retaining nut hole of the wheel
cover (Fig. 13).
Fig. 12 Wheel Cover Retaining Nuts
1 ± TIRE
2 ± VALVE STEM
3 ± LOCK-ON WHEEL COVER
4 ± WHEEL
5 ± WHEEL COVER RETAINING NUTS
Fig. 13 Wheel Cover Retaining Nut Retention
1 ± WHEEL COVER
2 ± WHEEL COVER RETAINING NUT
3 ± SMALL RETAINING TABS
4 ± LARGE RETAINING TAB
PLTIRES AND WHEELS 22 - 15

(3) When flange on retaining nut is past the 2
retaining tabs on the wheel cover, remove retaining
nut from wheel cover by pushing or pulling from hole
in wheel cover.
INSTALL
(1) Install retaining nut in hole of wheel cover
with retaining nut flange positioned under the large
retaining flange (Fig. 13).
(2) Push on hex of retaining nut forcing the retain-
ing nut flange past the 2 small retaining tabs in
wheel cover.
TIRE AND WHEEL ASSEMBLY
CAST WHEEL
REMOVAL
(1) Raise the vehicle. Refer to HOISTING in the
LUBRICATION AND MAINTENANCE section.
(2) Remove the wheel mounting nuts from the
studs.
(3) Remove the tire and wheel assembly from the
hub.
INSTALLATION
CAUTION: Installing the wheel mounting nuts with-
out having good metal-to-mental contact between
the back of the wheel and the hub mounted brake
disc or drum could cause the wheel to bind and
eventually cause loosening of the wheel mounting
nuts.
(1) Install the tire and wheel assembly on the hub
studs against the hub mounted brake disc or drum
using the hub pilot as a guide.
CAUTION: When installing the tire and wheel
assembly, never use oil or grease on studs or nuts.
(2) Install and lightly tighten the wheel mounting
nuts in the proper sequence (Fig. 14).
(3) Lower the vehicle.
(4) Progressively tighten the 5 wheel nuts in the
proper sequence until tightened to half of the speci-
fied torque (Fig. 14). Finally, tighten the wheel nuts
in the proper sequence to a torque of 135 N´m (100
ft. lbs.).
STEEL WHEEL
REMOVAL
(1) Raise the vehicle. Refer to HOISTING in the
LUBRICATION AND MAINTENANCE section.CAUTION: When removing the lock-on wheel cover,
do not attempt to pry the wheel cover off the wheel.
This can result in damage to the wheel cover. The
wheel cover is removed by unthreading the wheel
cover retaining nuts and pulling it off the wheel by
hand.
NOTE: When unthreading the lock-on wheel cover
retaining nuts (Fig. 15) from the wheel nuts it is rec-
ommended that a hand wrench be used and not an
impact wrench. Use of an impact wrench could
result in damage to the lock-on wheel cover retain-
ing nuts.
(2) Unthread the nuts attaching the wheel cover to
the wheel mounting nuts (Fig. 15).
Fig. 14 Tightening Wheel Nuts
Fig. 15 Wheel Cover Retaining Nuts
1 ± TIRE
2 ± VALVE STEM
3 ± LOCK-ON WHEEL COVER
4 ± WHEEL
5 ± WHEEL COVER RETAINING NUTS
22 - 16 TIRES AND WHEELSPL
REMOVAL AND INSTALLATION (Continued)

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
Alternate Good Trip
Alternate Good Trips are used in place of Global
Good Trips for Comprehensive Components and
Major Monitors. If the Task Manager cannot run a
Global Good Trip because a component fault is stop-
ping the monitor from running, it will attempt to
count an Alternate Good Trip.
The Task Manager counts an Alternate Good Trip
for Comprehensive components when the following
conditions are met:
²Two minutes of engine run time
²No other faults occur
The Task Manager counts an Alternate Good Trip
for a Major Monitor when the monitor runs and
passes. Only the Major Monitor that failed needs to
pass to count an Alternate Good Trip.
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
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 twotrip 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 uti-
lizes both Short Term Compensation and Long Term
Adaptive 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 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.
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.
25 - 4 EMISSION CONTROL SYSTEMSPL
DESCRIPTION AND OPERATION (Continued)

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 uti-
lizes both Short Term Compensation and Long Term
Adaptive 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.
MALFUNCTION INDICATOR LAMP (MIL)
OPERATION
As a functional test, the Malfunction Indicator
Lamp (MIL) illuminates at key-on before engine
cranking. Whenever the Powertrain Control Module
(PCM) sets a Diagnostic Trouble Code (DTC) that
affects vehicle emissions, it illuminates the MIL. If a
problem is detected, the PCM sends a message over
the PCI Bus to the instrument cluster to illuminate
the lamp. The PCM illuminates the MIL only for
DTC's that affect vehicle emissions. The MIL stays
on continuously when the PCM has entered a
Limp-In mode or identified a failed emission compo-
nent or system. The MIL remains on until the DTC
is erased. Refer to the Diagnostic Trouble Code
charts in this group for emission related codes.
Also, the MIL either flashes or illuminates contin-
uously when the PCM detects active engine misfire.
Refer to Misfire Monitoring in this section.Additionally, the PCM may reset (turn off) the MIL
when one of the following occur:
²PCM does not detect the malfunction for 3 con-
secutive trips (except misfire and fuel system moni-
tors).
²PCM does not detect a malfunction while per-
forming three successive engine misfire or fuel sys-
tem tests. The PCM performs these tests while the
engine is operating within6375 RPM of and within
10 % of the load of the operating condition at which
the malfunction was first detected.
DRB III STATE DISPLAY TEST MODE
OPERATION
The switch inputs to the Powertrain Control Mod-
ule (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. From
the state display screen, access either State Display
Inputs and Outputs or State Display Sensors.
DRB III CIRCUIT ACTUATION TEST MODE
OPERATION
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 cor-
rectly.
DIAGNOSTIC TROUBLE CODES
DESCRIPTION
A Diagnostic Trouble Code (DTC) indicates the
PCM has recognized an abnormal condition in the
system.
Remember that DTC's are the results of a sys-
tem or circuit failure, but do not directly iden-
tify the failed component or components.
NOTE: For a list of DTC's, refer to the charts in this
section.
PLEMISSION CONTROL SYSTEMS 25 - 5
DESCRIPTION AND OPERATION (Continued)

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 output. The programmed memory
acts as a self calibration tool that the engine control-
ler uses to compensate for variations in engine spec-
ifications, sensor tolerances and engine fatigue over
the life span of the engine. By monitoring the actual
air-fuel ratio with the O2S (short term) and multiply-
ing that with the program long-term (adaptive) mem-
ory 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.
Monitor OperationÐFuel systems monitors do
not have a pre-test because they are continuously
running monitors. Therefore, the PCM constantly
monitors Short Term Compensation and Long Term
Adaptive memory.
Lean: If at anytime during a lean engine operation,
short term compensation multiplied by long term
adaptive exceeds a certain percentage for an
extended period, the PCM sets a Fuel System Lean
Fault for that trip and a Freeze Frame is entered.
Rich: If at anytime during a rich operation, Short
Term Compensation multiplied by Long Term Adap-
tive is less than a predetermined value, the PCM
checks the Purge Free Cells.
Purge Free Cells are values placed in Adaptive
Memory cells when the EVAP Purge Solenoid is OFF.
Two, three or four Purge Free cells are used. One cor-
responds to an Adaptive Memory cell at idle, the
other to a cell that is off-idle. For example, if a Purge
Free cell is labeled PFC1, it would hold the value for
Adaptive Memory cell C1 under non-purge condi-
tions.
If all Purge Free Cells are less than a certain per-
centage, and the Adaptive Memory factor is less than
a certain percentage, the PCM sets a Fuel System
Rich fault for that trip and a Freeze Frame is
entered.
The Fuel Monitor is a two trip monitor. The PCM
records engine data in Freeze Frame upon setting of
the first fault, or maturing code. When the fuel mon-
itor fails on a second consecutive trip, the code is
matured and the MIL is illuminated. The stored
Freeze Frame data is still from the first fault.
In order for the PCM to extinguish the MIL, the
Fuel Monitor must pass in a Similar Condition Win-
dow. The similar conditions relate to RPM and load.
The engine must be within a predetermined percent-
age of both RPM and load when the monitor runs to
count a good trip. As with all DTCs, three good tripsare required to extinguish the MIL and 40 warm up
cycles are required to erase the DTC. If the engine
does not run in a Similar Conditions Window, the
Task Manager extinguishes the MIL after 80 good
trips.
Enabling ConditionsÐThe following conditions
must be met to operate the fuel control monitor:
²PCM not in fuel crank mode (engine running)
²PCM in Closed Loop fuel control
²Fuel system updating Long Term Adaptive
²Fuel level above 15% of capacity
²Fuel level below 85% of capacity
Pending ConditionsÐThe Fuel Control Monitor
does not operate if the MIL is illuminated for any of
the following:
²Misfire Monitor
²Upstream O2S
²EVAP Purge Solenoid Electrical PCM Self Test
Fault
²Camshaft or Crankshaft Position Sensor
²Fuel Injectors
²Ignition Coil Primary
²Throttle Position (TPS) Sensor
²Engine Coolant Temperature (ECT) Sensor
²Manifold Absolute Pressure (MAP) Sensor
²Idle Air Control (IAC)
²5V Output Too Low
²EGR Monitor
²EGR Solenoid Circuit
²Vehicle Speed Sensor
²Oxygen Sensor Monitor
²Oxygen Sensor Heater Monitor
²Oxygen Sensor Electrical
²Idle Speed Rationality
²Intake Air Temperature
SuspendÐThe Task Manager will suspend
maturing a Fuel System fault if any of the following
are present:
²Oxygen Sensor Response, Priority 1
²O2 Heater, Priority 1
²Misfire Monitor, Priority 2
EVAPORATIVE EMISSIONS MONITOR
LEAK DETECTION PUMP MONITORÐThe
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 func-
tions 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.
PLEMISSION CONTROL SYSTEMS 25 - 17
DESCRIPTION AND OPERATION (Continued)

NOTE: Comprehensive component monitors are
continuous. Therefore, enabling conditions do not
apply.
Input RationalityÐWhile input signals to the
PCM are constantly being monitored for electrical
opens and shorts, they are also tested for rationality.
This means that the input signal is compared against
other inputs and information to see if it makes sense
under the current conditions.
PCM sensor inputs that are checked for rationality
include:
²Manifold Absolute Pressure (MAP) Sensor
²Oxygen Sensor (O2S)
²Engine Coolant Temperature (ECT) Sensor
²Camshaft Position (CMP) Sensor
²Vehicle Speed Sensor
²Crankshaft Position (CKP) Sensor
²Intake Air Temperature (IAT) Sensor
²Throttle Position (TPS) Sensor
²Ambient/Battery Temperature Sensors
²Power Steering Switch
²Oxygen Sensor Heater
²Engine Controller
²Brake Switch
²Leak Detection Pump Switch
²P/N Switch
²Trans Controls
Output FunctionalityÐPCM outputs are tested
for functionality in addition to testing for opens and
shorts. When the PCM provides a voltage to an out-
put component, it can verify that the command was
carried out by monitoring specific input signals for
expected changes. For example, when the PCM com-
mands the Idle Air Control (IAC) Motor to a specific
position under certain operating conditions, it expects
to see a specific (target) idle speed (RPM). If it does
not, it stores a DTC.
PCM outputs monitored for functionality include:
²Fuel Injectors
²Ignition Coils
²Torque Converter Clutch Solenoid
²Idle Air Control
²Purge Solenoid
²EGR Solenoid
²LDP Solenoid
²Radiator Fan Control
²Trans Controls
OXYGEN SENSOR (O2S) MONITOR
DESCRIPTIONÐEffective control of exhaust
emissions is achieved by an oxygen feedback system.
The most important element of the feedback system
is the O2S. The O2S is located in the exhaust path.
Once it reaches operating temperature 300É to 350ÉC
(572É to 662ÉF), the sensor generates a voltage that
is inversely proportional to the amount of oxygen inthe exhaust. When there is a large amount of oxygen
in the exhaust caused by a lean condition, the sensor
produces a low voltage, below 450 mV. When the oxy-
gen 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. This main-
tains a 14.7 to 1 air fuel (A/F) ratio. At this mixture
ratio, the catalyst works best to remove hydrocarbons
(HC), carbon monoxide (CO) and nitrous oxide (NOx)
from the exhaust.
The O2S is also the main sensing element for the
EGR, Catalyst and Fuel Monitors.
The O2S may fail in any or all of the following
manners:
²Slow response rate (Big Slope)
²Reduced output voltage (Half Cycle)
²Heater Performance
Slow Response Rate (Big Slope)ÐResponse
rate is the time required for the sensor to switch
from lean to rich signal output once it is exposed to a
richer than optimum A/F mixture or vice versa. As
the PCM adjusts the air/fuel ratio, the sensor must
be able to rapidly detect the change. As the sensor
ages, it could take longer to detect the changes in the
oxygen content of the exhaust gas. The rate of
change that an oxygen sensor experiences is called
'Big Slope'. The PCM checks the oxygen sensor volt-
age in increments of a few milliseconds.
Reduced Output Voltage (Half Cycle)ÐThe
output voltage of the O2S ranges from 0 to 1 volt. A
good sensor can easily generate any output voltage in
this range as it is exposed to different concentrations
of oxygen. To detect a shift in the A/F mixture (lean
or rich), the output voltage has to change beyond a
threshold value. A malfunctioning sensor could have
difficulty changing beyond the threshold value. Each
time the voltage signal surpasses the threshold, a
counter is incremented by one. This is called the Half
Cycle Counter.
Heater PerformanceÐThe heater is tested by a
separate monitor. Refer to the Oxygen Sensor Heater
Monitor.
OPERATIONÐAs the Oxygen Sensor signal
switches, the PCM monitors the half cycle and big
slope signals from the oxygen sensor. If during the
test neither counter reaches a predetermined value, a
malfunction is entered and a Freeze Frame is stored.
Only one counter reaching its predetermined value is
needed for the monitor to pass.
The Oxygen Sensor 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
25 - 20 EMISSION CONTROL SYSTEMSPL
DESCRIPTION AND OPERATION (Continued)

Pending ConditionsÐThere are not conditions
or situations that prompt conflict or suspension of
testing. The oxygen sensor heater test is not run
pending resolution of MIL illumination due to oxygen
sensor failure.
SuspendÐThere 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 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 atotally ineffective catalyst, this ratio will be one-to-
one, indicating that no oxidation occurs in the device.
The system must be monitored so that when cata-
lyst efficiency deteriorates and exhaust emissions
increase to over the legal limit, the MIL (check
engine lamp) will be illuminated.
Monitor OperationÐTo monitor catalyst effi-
ciency, the PCM expands the rich and lean switch
points of the heated oxygen sensor. With extended
switch points, the air/fuel mixture runs richer and
leaner to overburden the catalytic converter. Once
the test is started, the air/fuel mixture runs rich and
lean and the O2 switches are counted. A switch is
counted when an oxygen sensor signal goes from
below the lean threshold to above the rich threshold.
The number of Rear O2 sensor switches is divided by
the number of Front O2 sensor switches to determine
the switching ratio.
The test runs for 20 seconds. As catalyst efficiency
deteriorated over the life of the vehicle, the switch
rate at the downstream sensor approaches that of the
upstream sensor. If at any point during the test
period the switch ratio reaches a predetermined
value, a counter is incremented by one. The monitor
is enabled to run another test during that trip. When
the test fails three times, the counter increments to
three, a malfunction is entered, and a Freeze Frame
is stored. When the counter increments to three dur-
ing the next trip, the code is matured and the MIL is
illuminated. If the test passes the first, no further
testing is conducted during that trip.
The MIL is extinguished after three consecutive
good trips. The good trip criteria for the catalyst
monitor is more stringent than the failure criteria. In
order to pass the test and increment one good trip,
the downstream sensor switch rate must be less than
80% of the upstream rate (60% for manual transmis-
sions). The failure percentages are 90% and 70%
respectively.
Enabling ConditionsÐThe following conditions
must typically be met before the PCM runs the cat-
alyst monitor. Specific times for each parameter may
be different from engine to engine.
²Accumulated drive time
²Enable time
²Ambient air temperature
²Barometric pressure
²Catalyst warm-up counter
²Engine coolant temperature
²Accumulated throttle position sensor
²Vehicle speed
²MAP
²RPM
²Engine in closed loop
²Fuel level
25 - 22 EMISSION CONTROL SYSTEMSPL
DESCRIPTION AND OPERATION (Continued)