Chrysler PT Cruiser. Manual — part 986

are met. If the monitor fails, the PCM stores a
maturing fault and a Freeze Frame is entered. If two
consecutive tests fail, a DTC is stored. Because the
ignition is OFF, the MIL is illuminated at the begin-
ning of the next key cycle, after the 2nd failure.

Enabling Conditions—The following conditions

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

• Engine run time of at least 5.1 minutes

• Key OFF power down

• Battery voltage of at least 10 volts

• Sufficient Oxygen Sensor cool down
Pending Conditions—There are not conditions or

situations that prompt conflict or suspension of test-
ing. The oxygen sensor heater test is not run pending
resolution of MIL illumination due to oxygen sensor
failure.

Suspend—There are no conditions which exist for

suspending the Heater Monitor.

CATALYST MONITOR

To comply with clean air regulations, vehicles are

equipped with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide.

Normal vehicle miles or engine misfire can cause a

catalyst to decay. A meltdown of the ceramic core can
cause a reduction of the exhaust passage. This can
increase vehicle emissions and deteriorate engine
performance, driveability and fuel economy.

The catalyst monitor uses dual oxygen sensors

(O2S’s) to monitor the efficiency of the converter. The
dual O2S strategy is based on the fact that as a cat-
alyst deteriorates, its oxygen storage capacity and its
efficiency are both reduced. By monitoring the oxy-
gen storage capacity of a catalyst, its efficiency can
be indirectly calculated. The upstream O2S is used to
detect the amount of oxygen in the exhaust gas
before the gas enters the catalytic converter. The
PCM calculates the A/F mixture from the output of
the O2S. A low voltage indicates high oxygen content
(lean mixture). A high voltage indicates a low content
of oxygen (rich mixture).

When the upstream O2S detects a high oxygen

condition, there is an abundance of oxygen in the
exhaust gas. A functioning converter would store this
oxygen so it can use it for the oxidation of HC and
CO. As the converter absorbs the oxygen, there will
be a lack of oxygen downstream of the converter. The
output of the downstream O2S will indicate limited
activity in this condition.

As the converter loses the ability to store oxygen,

the condition can be detected from the behavior of
the downstream O2S. When the efficiency drops, no
chemical reaction takes place. This means the con-
centration of oxygen will be the same downstream as

upstream. The output voltage of the downstream
O2S copies the voltage of the upstream sensor. The
only difference is a time lag (seen by the PCM)
between the switching of the O2S’s.

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 (check
engine lamp) will be illuminated.

Monitor Operation—To 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 Conditions—The 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.

• Accumulated drive time

• Enable time

25 - 4

EMISSIONS CONTROL

PT

EMISSIONS CONTROL (Continued)

• Ambient air temperature

• Barometric pressure

• Catalyst warm-up counter

• Engine coolant temperature

• Accumulated throttle position sensor

• Vehicle speed

• MAP

• RPM

• Engine in closed loop

• Fuel level
Pending Conditions—
• Misfire DTC

• Front Oxygen Sensor Response

• Front Oxygen Sensor Heater Monitor

• Front Oxygen Sensor Electrical

• Rear Oxygen Sensor Rationality (middle check)

• Rear Oxygen Sensor Heater Monitor

• Rear Oxygen Sensor Electrical

• Fuel System Monitor

• All TPS faults

• All MAP faults

• All ECT sensor faults

• Purge flow solenoid functionality

• Purge flow solenoid electrical

• All PCM self test faults

• All CMP and CKP sensor faults

• All injector and ignition electrical faults

• Idle Air Control (IAC) motor functionality

• Vehicle Speed Sensor

• Brake switch

• Intake air temperature
Conflict—The catalyst monitor does not run if any

of the following are conditions are present:

• EGR Monitor in progress

• Fuel system rich intrusive test in progress

• EVAP Monitor in progress

• Time since start is less than 60 seconds

• Low fuel level

• Low ambient air temperature

• Ethanel content learn is taking place and the

ethenal used once flag is set

Suspend—The Task Manager does not mature a

catalyst fault if any of the following are present:

• Oxygen Sensor Monitor, Priority 1

• Upstream Oxygen Sensor Heater, Priority 1

• EGR Monitor, Priority 1

• EVAP Monitor, Priority 1

• Fuel System Monitor, Priority 2

• Misfire Monitor, Priority 2

DESCRIPTION - VEHICLE EMISSION CONTROL
INFORMATION LABEL

All models have a Vehicle Emission Control Infor-

mation (VECI) Label. Chrysler permanently attaches
the label in the engine compartment. It cannot be

removed without defacing information and destroying
the label.

The label contains the vehicle’s emission specifica-

tions and vacuum hose routings. All hoses must be
connected and routed according to the label.

DESCRIPTION - TRIP DEFINITION

A “Trip” means vehicle operation (following an

engine-off period) of duration and driving mode such
that all components and systems are monitored at
least once by the diagnostic system. The monitors
must successfully pass before the PCM can verify
that a previously malfunctioning component is meet-
ing the normal operating conditions of that compo-
nent. For misfire or fuel system malfunction, the
MIL may be extinguished if the fault does not recur
when monitored during three subsequent sequential
driving cycles in which conditions are similar to
those under which the malfunction was first deter-
mined.

Anytime the MIL is illuminated, a DTC is stored.

The DTC can self erase only after the MIL has been
extinguished. Once the MIL is extinguished, the
PCM must pass the diagnostic test for the most
recent DTC for 40 warm-up cycles (80 warm-up
cycles for the Fuel System Monitor and the Misfire
Monitor). A warm-up cycle can best be described by
the following:

• The engine must be running

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

from the time when the engine was started

• Engine coolant temperature must crossover

160°F

• A “driving cycle” that consists of engine start up

and engine shut off.

Once the above conditions occur, the PCM is con-

sidered to have passed a warm-up cycle. Due to the
conditions required to extinguish the MIL and erase
the DTC, it is most important that after a repair has
been made, all DTC’s be erased and the repair veri-
fied by running 1–good trip.

OPERATION - NON-MONITORED CIRCUITS

The PCM does not monitor all circuits, systems

and conditions that could have malfunctions causing
driveability problems. However, problems with these
systems may cause the PCM to store diagnostic trou-
ble codes for other systems or components. For exam-
ple, a fuel pressure problem will not register a fault
directly, but could cause a rich/lean condition or mis-
fire. This could cause the PCM to store an oxygen
sensor or misfire diagnostic trouble code.

The major non-monitored circuits are listed below

along with examples of failures modes that do not
directly cause the PCM to set a DTC, but for a sys-
tem that is monitored.

PT

EMISSIONS CONTROL

25 - 5

EMISSIONS CONTROL (Continued)

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, fuel system, or mis-
fire 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. The misfire will however,
increase the oxygen content in the exhaust, deceiving
the PCM in to thinking the fuel system is too lean.
Also see misfire detection. There are DTC’s that can
detect misfire and Ionization shorts in the secondary
ignition circuit, refer to the Powertrain Diagnostic
manual for more information

CYLINDER COMPRESSION

The PCM cannot detect uneven, low, or high engine

cylinder compression. Low compression lowers O2
content in the exhaust. Leading to fuel system, oxy-
gen sensor, or misfire detection fault.

EXHAUST SYSTEM

The PCM cannot detect a plugged, restricted or

leaking exhaust system. It may set a EGR (if
equipped) or Fuel system or O2S 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.

VACUUM ASSIST

The PCM cannot detect leaks or restrictions in the

vacuum circuits of vacuum assisted engine control
system devices. However, these could cause the PCM
to store a MAP sensor diagnostic trouble code and
cause a high idle condition.

PCM SYSTEM GROUND

The PCM cannot determine a poor system ground.

However, one or more diagnostic trouble codes may
be generated as a result of this condition. The mod-
ule should be mounted to the body at all times,
including when diagnostics are performed.

PCM CONNECTOR ENGAGEMENT

The PCM may not be able to determine spread or

damaged connector pins. However, it might store
diagnostic trouble codes as a result of spread connec-
tor pins.

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 (Check
Engine) Lamp will be illuminated. These monitors
generate Diagnostic Trouble Codes that can be dis-
played with the a DRBIII

t scan tool.

The following is a list of the system monitors:
• EGR Monitor (if equipped)

• Misfire Monitor

• Fuel System Monitor

• Oxygen Sensor Monitor

• Oxygen Sensor Heater Monitor

• Catalyst Monitor

• Evaporative System Leak Detection Monitor (if

equipped)

Following is a description of each system monitor,

and its DTC.

Refer to the appropriate Powertrain Diagnos-

tics Procedures manual for diagnostic proce-
dures.

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 temperatures of 300° to 350°C (572° to 662°F),
the sensor generates a voltage that is inversely pro-
portional to the amount of oxygen in the exhaust.
The information obtained by the sensor is used to
calculate the fuel injector pulse width. The PCM is
programmed to maintain the optimum air/fuel ratio.

25 - 6

EMISSIONS CONTROL

PT

EMISSIONS CONTROL (Continued)

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 (if equipped), Catalyst and Fuel Monitors.

The O2S may 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 (voltages are offset by 2.5 volts on NGC vehi-
cles). 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) DTC as well as

a O2S heater DTC, the O2S heater fault MUST be
repaired first. After the O2S fault is repaired, verify
that the heater circuit is operating correctly.

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 temperatures of 300° to 350°C (572 ° to 662°F),
the sensor generates a voltage that is inversely pro-
portional to the amount of oxygen in the exhaust.
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 nitrogen oxide
(NOx) from the exhaust.

The voltage readings taken from the O2S are very

temperature sensitive. The readings are not accurate
below 300°C. Heating of the O2S is done to allow the
engine controller to shift to closed loop control as
soon as possible. The heating element used to heat
the O2S must be tested to ensure that it is heating
the sensor properly.

The O2S circuit is monitored for a drop in voltage.

The sensor output is used to test the heater by iso-
lating the effect of the heater element on the O2S
output voltage from the other effects.

EGR MONITOR (if equipped)

The Powertrain Control Module (PCM) performs

an on-board diagnostic check of the EGR system.

The EGR monitor is used to test whether the EGR

system is operating within specifications. The diag-
nostic check activates only during selected engine/
driving conditions. When the conditions are met, the
EGR is turned off (solenoid energized) and the O2S
compensation control is monitored. Turning off the
EGR shifts the air fuel (A/F) ratio in the lean direc-
tion. The O2S data should indicate an increase in the
O2 concentration in the combustion chamber when
the exhaust gases are no longer recirculated. While
this test does not directly measure the operation of
the EGR system, it can be inferred from the shift in
the O2S data whether the EGR system is operating
correctly. Because the O2S is being used, the O2S
test must pass its test before the EGR test. Also
looks at EGR linear potentiometer for feedback.

MISFIRE MONITOR

Excessive engine misfire results in increased cata-

lyst temperature and causes an increase in HC emis-
sions. 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 crank-
shaft 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 nitro-
gen and carbon monoxide. The catalyst works best
when the air fuel (A/F) ratio is at or near the opti-
mum of 14.7 to 1.

The PCM is programmed to maintain the optimum

air/fuel ratio. This is done by making short term cor-
rections in the fuel injector pulse width based on the
O2S 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 air-fuel
ratio with the O2S (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 malfunc-
tion occurs such that the PCM cannot maintain the
optimum A/F ratio, then the MIL will be illuminated.

PT

EMISSIONS CONTROL

25 - 7

EMISSIONS CONTROL (Continued)