Chrysler Town, Dodge Caravan. Manual - part 549

OBDII Monitor Run Process
2.0L/2.4L NGC Vehicles

The following procedure has been established to

assist Technicians in the field with enabling and
running OBDII Monitors. The order listed in the
following procedure is intended to allow the techni-
cian to effectively complete each monitor and to set
the CARB Readiness Status in the least time pos-
sible.

**NOTE**

A. Once the monitor run process has begun, do

not turn off the ignition. By turning the igni-
tion key off, monitor enabling conditions will
be lost. NVLD Monitor runs after key off.

B. By performing a Battery Disconnect, or Se-

lecting Erase DTCs, the CARB Readiness and
all additional OBDII information will be
cleared.

Monitor Preliminary Checks:

1. Plug a DRBIII

t into the vehicle’s DLC.

2. Turn the ignition, KEY ON–ENGINE OFF.

Watch for MIL lamp illumination during the
bulb check. MIL lamp must have illuminated, if
not, repair MIL lamp.

3. On the DRB III

t Select #1 DRB III Standalone.

4. Select #1 1998-2002 Diagnostics

5. Select #1 Engine

6. Select #2 DTCs and Related Functions

7. Select #1 Read DTCs

*Verify that No Emissions Related DTCs are
Present.
*If an Emissions DTC is Present, the OBD II
Monitors may not run and the CARB Readiness
will not update.
*The Emissions related DTC, will need to be
repaired, then cleared. By clearing DTCs, the
OBD Monitors will need to be run and completed
to set the CARB Readiness Status.

8. Return to Engine Select Function Menu and

Select #9, OBD II Monitors.

9. Select #3 CARB Readiness Status.

Do all the CARB Readiness Status Locations read
YES?

*YES, then all monitors have been completed and
this vehicle is ready to be I/M or Emission Tested.
*NO, then the following procedure needs to be
followed to run/complete all available monitors.

**NOTE**
A. Only the monitors, which are not YES in the

CARB Readiness Status, need to be completed.

B. Specific criteria need to be met for each monitor.

Each monitor has a Pre-Test screen to assist in
running the monitor.

For additional information, refer to the Chrysler
Corporation Technical Training Workbook titled
On Board Diagnostics: OBDII/EOBD, part num-
ber 81-699-01050.

The most efficient order to run the monitors has
been outlined below, including suggestions to aid
the process.

A. NATURAL VACUUM LEAK DETECTION WITH
PURGE MONITOR

This monitor requires a cool down cycle, usually

an overnight soak for at least 8 hours without the
engine running. The ambient temperature must
decrease overnight – parking the vehicle outside is
advised. To run this test the fuel level must be
between 15-85% full. For the monitor run condi-
tions select the EVAP MON PRE-TEST in the
DRB III

t, OBD II Monitors Menu. The Purge mon-

itor will run if the small leak test reports a pass.
Criteria for NVLD monitor.

1. Engine off time greater than @ one hour

2. Fuel Level between 15% and 85%

3. Start Up ECT and IAT within 10°C (18°F).

4. Vehicle started and run until Purge Monitor

reports a result.

NOTE: If the vehicle does not report a result
and the conditions where correct. It may take
up to two weeks to fail the small leak monitor.
DO NOT use this test to attempt to determine
a

fault.

Use

the

appropriate

service

information procedure for finding a small
leak. If there are no faults and the conditions
are correct this test will run and report a
pass. Note the Small leak test can find leaks
less than 10 thousands of an inch. If a small
leak is present it takes approximately one
week of normal driving to report a failure.

B. CATALYST/O2 MONITOR

With NGC, Catalyst and O2 Monitor information

are acquired and processed at the same time. Most
vehicles will need to be driven at highway speed
(<50 mph) for a few minutes. Some trucks run the
monitor at idle in drive. If the vehicle is equipped
with a manual transmission, using 4

gear may

assist in meeting the monitor running criteria. For
the monitor run conditions, select the BANK 1 CAT
MON PRE-TEST in the DRB III

t, OBD II Monitors

Menu.

C. EGR MONITOR

The EGR monitor now runs in a closed throttle

decel or at idle on a warm vehicle. However, it is
necessary to maintain the TPS, Map and RPM
ranges to allow the monitor to complete itself. For

GENERAL INFORMATION

the monitor run conditions, select the EGR PRE-
TEST in the DRB III

t, OBD II Monitors Menu.

D. 02 SENSOR HEATER MONITOR

This monitor is now continuously running once

the heaters are energized. Pass information will be
processed at power down. For the monitor run
conditions, select the O2S HEATER MON PRE-
TEST in the DRB III

t, OBD II Monitors Menu.

OBDII Monitor Run Process
3.3L/3.8L SBEC Vehicles

The following procedure has been established to

**NOTE**

A. Once the monitor run process has begun, do

not turn off the ignition. By turning the igni-
tion key off, monitor enabling conditions will
be lost. Only the 02 Heater Monitor runs after
key off.

B. By performing a Battery Disconnect, or Se-

lecting Erase DTCs, the CARB Readiness and
all

additional

OBD

information

will

cleared.

Monitor Preliminary Checks:

1. Plug a DRBIII into the vehicle’s DLC.

2. Turn the ignition, KEY ON–ENGINE OFF.

Watch for MIL lamp illumination during the
bulb check. MIL lamp must have illuminated, if
not, repair MIL lamp.

3. On the DRB III Select #1 DRB III Standalone.

4. Select #1 1998-2002 Diagnostics

5. Select #1 Engine

6. Select #2 DTCs and Related Functions

7. Select #1 Read DTCs

8. Return to Engine Select Function Menu and

Select #9, OBD II Monitors.

9. Select #3 CARB Readiness Status.

Do all the CARB Readiness Status Locations read
YES?

*YES, then all monitors have been completed and
this vehicle is ready to be I/M or Emission Tested.
*NO, then the following procedure needs to be
followed to run/complete all available monitors.

**NOTE**
A. Only the monitors, which are not YES in the

CARB Readiness Status, need to be completed.

B. Specific criteria need to be met for each monitor.

Each monitor has a Pre-Test screen to assist in
running the monitor. For additional informa-
tion, refer to the Chrysler Corporation Technical
Training Workbook titled On Board Diagnostics,
part number 81-699-97094.

The most efficient order to run the monitors has
been outlined below, including suggestions to aid
the process.

2. EVAPORATIVE LEAK DETECTION MONITOR
(IF THE VEHICLE IS EQUIPPED WITH A LDP
SYSTEM)

This monitor requires a cold start, usually an

overnight soak or parked for at least 8 hours with-
out the engine running. The engine coolant must be
within 10 degrees of ambient/battery temperature,
and the sensed Ambient (outside) Temperature
must be between approximately 40°F and 90°F. For
the monitor run conditions select the EVAP LDP
MON PRE-TEST in the DRB III, OBD II Monitors
Menu.

1. Catalyst Monitor

The vehicle will need to be driven at highway

speed for a few minutes. If the vehicle is equipped
with a manual transmission, using 4

gear may

assist in meeting the monitor running criteria. For
the monitor run conditions, select the EWMA CAT
MON PRE-TEST in the DRB III, OBD II Monitors
Menu.

2. EGR Monitor

The EGR monitor enable conditions are basic.

However, it is necessary to maintain the TPS, Map
and RPM ranges to allow the monitor to complete
itself. For the monitor run conditions, select the
EGR PRE-TEST in the DRB III, OBD II Monitors
Menu.

3. O2 Sensor Monitor

The vehicle will need to be driven for a period of

time and brought to a stop for a short period of time
with the Automatic Transmission left in Drive. The
O2S Monitor will not run in Park or Neutral on an
Automatic Transmission equipped vehicle. For the
monitor run conditions, select the O2S MON PRE-
TEST in the DRB III, OBD II Monitors Menu.

4. Purge Monitor

All the Purge Free (PF) cells must update on the

ADAPTIVE MEMORY screen before the Purge

GENERAL INFORMATION

Flow Monitor will run. For the monitor run condi-
tions, select the PURGE FLOW MON PRE-TEST in
the DRB III, OBD II Monitors Menu. The Purge
Flow Monitor will not run in Park or Neutral on an
Automatic Transmission equipped vehicle. The
Purge Flow Monitor will attempt to run every
other throttle closure. If all of the parameters are
met and it still does not run, with your foot firmly
on the Service Brake, slightly (1/4) open the Throt-
tle and quickly close the Throttle. This will allow
the Purge Free update to happen, and then the
Purge Flow Monitor will Run.

5. O2 Sensor Heater Monitor

Make sure the Open Throtle Time on the O2

Heater Pre-Test Screen has been exceeded, if not,
more driving will be necessary to enable this Mon-
itor. This is an ignition key OFF monitor. Do this
monitor only after all other monitors have been
completed. It will be necessary to turn the ignition
key back on after the DRB III goes to No Response,
which indicates that the O2 Heater Monitor has
completed and the PCM has gone to sleep (shut off)
(approximately 3 minutes). Turn the Ignition Key
back ON to see if the CARB Readiness is YES. For
the

monitor

run

conditions,

select

the

O2S

HEATER MON PRE-TEST in the DRB III, OBD II
Monitors Menu.

3.2.3

OTHER CONTROLS

CHARGING SYSTEM (NGC)

The charging system is turned on when the

engine is started. The Generator field is control by
the PCM using a 12-volt high-side driver and a body
ground circuit. The Generator output voltage is
determined by the PCM. When more system voltage
is needed, the PCM will applies a longer duty cycle
using the 12-volt high-side drive and shortens duty
cycle or none at all when less voltage is needed.

O2 SENSOR (NGC)

The O2 system with ignition on and engine off

has a normalized O2 voltage of around 5 volts as
displayed on the DRBIII or measured with a high
impedance voltmeter. As the O2 sensor starts gen-
erating a signal the voltage will move towards 2.5
volts. The voltage will typically vary between 2.5
volts and 3.5 volts on a normal running engine. The
goal voltage is also typically between 2.5 and 3.5
volts. This implies that the 0-volt through 1-volt
range that you are used to is still valid, only it is
shifted up by a 2.5 volt offset. This 2.5 volt supply is
being delivered through the sensor return line.

SPEED CONTROL SYSTEM

The PCM controls vehicle speed by operation of

the speed control servo vacuum and vent solenoids.

Energizing the vacuum solenoid applies vacuum to
the servo to increase throttle position. Operation of
the vent solenoid slowly releases the vacuum allow-
ing throttle position to decrease. A special vacuum
dump solenoid allows immediate release of the
throttle during speed control operation.

Speed control may be cancelled by braking, driver

input using the speed control switches, shifting into
neutral, excessive engine speed (wheels spinning),
or turning the ignition off.

NOTE: If two speed control switches are
selected simultaneously, the PCM will detect
an illegal switch operation and turn the speed
control off.

NATURAL VACUUM LEAK DETECTION (NVLD) –
IF EQUIPPED

The Natural Vacuum Leak Detection (NVLD)

system is the next generation evaporative leak
detection system that will first be used on vehicles
equipped with the Powertrain Control Module
(PCM) or Next Generation Controller (NGC) start-
ing in 2002 M.Y. This new system replaces the leak
detection pump as the method of evaporative sys-
tem leak detection. The current CARB requirement
is to detect a leak equivalent to a 0.020

9 (0.5 mm)

hole. This system has the capability to detect holes
of this size very dependably.

The basic leak detection theory employed with

NVLD is the

9Gas Law9. This is to say that the

pressure in a sealed vessel will change if the tem-
perature of the gas in the vessel changes. The vessel
will only see this effect if it is indeed sealed. Even
small leaks will allow the pressure in the vessel to
come to equilibrium with the ambient pressure.

In addition to the detection of very small leaks,

this system has the capability of detecting medium
as well as large evaporative system leaks.

THE NVLD UTILIZES THE GAS LAW
PRINCIPLES

A vent valve seals the canister vent during engine

off conditions. If the vapor system has a leak of less
than the failure threshold, the evaporative system
will be pulled into a vacuum, either due to the cool
down from operating temperature or diurnal ambi-
ent temperature cycling. The diurnal effect is con-
sidered one of the primary contributors to the leak
determination by this diagnostic. When the vacuum
in the system exceeds about 1

9 H2O (0.25 KPA), a

vacuum switch closes. The switch closure sends a
signal to the PCM. The PCM, via appropriate logic
strategies (described below), utilizes the switch
signal, or lack thereof, to make a determination of
whether a leak is present.

GENERAL INFORMATION

THE NVLD DEVICE AND HOW IT FUNCTIONS

The NVLD Assembly is designed with a normally

open vacuum switch, a normally closed solenoid,
and a seal, which is actuated by both the solenoid
and a diaphragm. The NVLD is located on the
atmospheric vent side of the canister.

The normally open vacuum switch will close with

about 1

9 H2O (0.25 KPA) vacuum in the evaporative

system. The diaphragm actuates the switch. This is
above the opening point of the fuel inlet check valve
in the fill tube so cap off leaks can be detected.
Submerged fill systems must have recirculation
lines that do not have the in-line normally closed
check valve that protects the system from failed
nozzle liquid ingestion, in order to detect cap off
conditions.

The normally closed valve in the NVLD is in-

tended to maintain the seal on the evaporative
system during the engine off condition. If vacuum in
the evaporative system exceeds 3

9 to 69 H2O (0.75 to

1.5 KPA), the valve will be pulled off the seat,
opening the seal. This will protect the system from
excessive vacuum as well as allowing sufficient
purge flow in the event that the solenoid was to
become inoperative. The solenoid actuates the valve
to unseal the canister vent while the engine is
running. It also will be used to close the vent during
the medium and large leak tests and during the
purge flow check. This solenoid requires initial 1.5
amps of current to pull the valve open but after 100
ms. will be duty cycled down to an average of about
150 mA for the remainder of the drive cycle.

Another feature in the NVLD Assembly is a

diaphragm that will open the seal with pressure in
the evaporative system. The seal will be opened at
about 0.5

9 H2O (0.12 KPA) pressure to permit the

venting of vapors during refueling. An added bene-
fit to this is that it will also allow the tank to
9breathe9 during increasing temperatures, thus lim-
iting the pressure in the tank to this low level. This
is beneficial because the induced vacuum during a
subsequent declining temperature will achieve the
switch closed (pass threshold) sooner than if the
tank had to decay from a built up pressure.

The NVLD Assembly itself has 3 wires: Switch

sense, solenoid driver and ground. It also includes a
resistor to protect the switch from a short to battery
or a short to ground. The PCM utilizes a high-side
driver to energize and duty-cycle the solenoid.

THE PCM’S ROLE IN NVLD DIAGNOSIS:

The integral part of the diagnostic system that

makes engine-off leak detection possible is a special
circuit in the PCM controller. After the vehicle is
turned off, a special part of the controller stays alive
and monitors for an NVLD switch closure. This
circuit within the PCM is very specific in its func-
tion and consumes very little power. If a switch

closure is detected, it will log the event and time
from key-off, and then power down. This informa-
tion will be processed at the next key cycle.

NVLD LEAK DETECTION

Small Leak Test (Passive)

If, after a specified delay after key off (perhaps 5

minutes), the switch closes or is closed, the test will
be pass, indicating that there is no leak. The PCM
records the switch closure. The NVLD circuit in the
PCM will shut down for the remainder of that
particular engine off (soak) period. When the engine
is started, the switch closure is recorded as a

9Pass,9

and the timers that are recording accumulated time
are reset.

This diagnostic test can take at least a week to

mature a leak fault. A week has been chosen for this
because the vehicle will have been exposed to the
largest possible drive scenarios before a decision is
made (most vehicles should see both daily work and
weekend driving cycles). This also satisfies CARB’s
stated goal of getting 3 MIL illuminations within a
month for 0.020

9 (0.5 mm) leak detection diagnostic.

The diagnostics will log engine run time and

engine off time to determine when a week has
elapsed. There is a limit on the total amount of run
time that is applied to the one-week timer. There is
also a limit on the total soak time that will be
allowed to be applied to the one-week timer. There
will be a limit on the amount of accrued run time
during one specific drive that can be applied to the
one-week timer.

The enabling criteria to run this monitor are:

•

Fuel level less than 85%

•

Ambient temperature greater than 40 °F (4.4 °C)

Rationality Tests

1. The rationality check of the switch, solenoid and

seal will be performed as follows:

•

At key-on, the NVLD solenoid will be energized to
vent any vacuum that may be trapped in the
evaporative system from the previous soak. This
should result in an open switch condition.

•

The solenoid will be de-energized (to seal the
system) at the point where purge begins. The
system / NVLD component rationality passes for
that drive cycle if the switch closes after purge
begins.

•

The solenoid is then re-energized for the remain-
der of the drive cycle.

•

If the switch events are not seen in a certain
period of time, the rationality check will have
failed (2 trip rule).

GENERAL INFORMATION

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