engine DODGE RAM 1500 1998 2.G Workshop Manual

cial material for the R-134a system. Use only refrig-
erant oil of the type recommended for the A/C
compressor in the vehicle.
(13) Connect the liquid line to the condenser outlet
port.
(14) Install and tighten the nut that secures the
liquid line fitting to the condenser. Tighten the nut to
20 N´m (180 in. lbs.).
(15) Install the plastic cover onto the condenser
outlet stud.
(16) If equipped with the diesel engine, install the
passenger side battery tray (Refer to 8 - ELECTRI-
CAL/BATTERY SYSTEM/TRAY - INSTALLATION).
(17) If equipped with the diesel engine, install the
passenger side battery (Refer to 8 - ELECTRICAL/
BATTERY SYSTEM/BATTERY - INSTALLATION).
(18) Reconnect the battery negative cables.
(19) Evacuate the refrigerant system (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM EVACUATE).
(20) Charge the refrigerant system (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM CHARGE).
REFRIGERANT
DESCRIPTION
The refrigerant used in this air conditioning sys-
tem is a HydroFluoroCarbon (HFC), type R-134a.
Unlike R-12, which is a ChloroFluoroCarbon (CFC),
R-134a refrigerant does not contain ozone-depleting
chlorine. R-134a refrigerant is a non-toxic, non-flam-
mable, clear, and colorless liquefied gas.
Even though R-134a does not contain chlorine, it
must be reclaimed and recycled just like CFC-type
refrigerants. This is because R-134a is a greenhouse
gas and can contribute to global warming.
OPERATION
R-134a refrigerant is not compatible with R-12
refrigerant in an air conditioning system. Even a
small amount of R-12 added to an R-134a refrigerant
system will cause compressor failure, refrigerant oil
sludge or poor air conditioning system performance.
In addition, the PolyAlkylene Glycol (PAG) synthetic
refrigerant oils used in an R-134a refrigerant system
are not compatible with the mineral-based refriger-
ant oils used in an R-12 refrigerant system.
R-134a refrigerant system service ports, service
tool couplers and refrigerant dispensing bottles have
all been designed with unique fittings to ensure that
an R-134a system is not accidentally contaminated
with the wrong refrigerant (R-12). There are alsolabels posted in the engine compartment of the vehi-
cle and on the compressor identifying to service tech-
nicians that the air conditioning system is equipped
with R-134a.
REFRIGERANT LINE COUPLER
DESCRIPTION
Spring-lock type refrigerant line couplers are used
to connect some of the refrigerant lines and other
components to the refrigerant system. These couplers
require a special tool for disengaging the two coupler
halves.
OPERATION
The spring-lock coupler is held together by a garter
spring inside a circular cage on the male half of the
fitting (Fig. 27). When the two coupler halves are
connected, the flared end of the female fitting slips
behind the garter spring inside the cage on the male
fitting. The garter spring and cage prevent the flared
end of the female fitting from pulling out of the cage.
Two O-rings on the male half of the fitting are
used to seal the connection. These O-rings are com-
patible with R-134a refrigerant and must be replaced
with O-rings made of the same material.
Secondary clips are installed over the two con-
nected coupler halves at the factory for added protec-
tion. In addition, some models have a plastic ring
that is used at the factory as a visual indicator to
confirm that these couplers are connected. After the
Fig. 27 Spring-Lock Coupler - Typical
1 - MALE HALF SPRING-LOCK COUPLER
2 - FEMALE HALF SPRING-LOCK COUPLER
3 - SECONDARY CLIP
4 - CONNECTION INDICATOR RING
5 - COUPLER CAGE
6 - GARTER SPRING
7 - COUPLER CAGE
8 - O-RING SEALS
DRPLUMBING 24 - 67
LIQUID LINE (Continued)

coupler is connected, the plastic indicator ring is no
longer required; however, it will remain on the refrig-
erant line near the coupler cage.
REMOVAL
(1) Recover the refrigerant from the refrigerant
system (Refer to 24 - HEATING & AIR CONDITION-
ING/PLUMBING/REFRIGERANT - STANDARD
PROCEDURE).
(2) Remove the secondary retaining clip from the
spring-lock coupler.
(3) Fit the proper size A/C line disconnect tool
(Special Tool Kit 7193 or equivalent) over the spring-
lock coupler cage (Fig. 28).
(4) Close the two halves of the A/C line disconnect
tool around the spring-lock coupler.
NOTE: The garter spring may not release if the A/C
line disconnect tool is cocked while pushing it into
the coupler cage opening.
(5) Push the A/C line disconnect tool into the open
side of the coupler cage to expand the garter spring.
Once the garter spring is expanded and while still
pushing the disconnect tool into the open side of the
coupler cage, pull on the refrigerant line attached to
the female half of the coupler fitting until the flange
on the female fitting is separated from the garter
spring and cage on the male fitting within the dis-
connect tool.
(6) Open and remove the A/C line disconnect tool
from the disconnected spring-lock coupler.(7) Complete the separation of the two halves of
the coupler fitting. Inspect the O-ring seals and mat-
ing areas for damage.
INSTALLATION
(1) Check to make sure that the garter spring is
located within the cage of the male coupler fitting,
and that the garter spring is not damaged.
(a) If the garter spring is missing, install a new
spring by pushing it into the coupler cage opening.
(b) If the garter spring is damaged, remove it
from the coupler cage with a small wire hook (DO
NOT use a screwdriver) and install a new garter
spring.
(2) Clean any dirt or foreign material from both
halves of the coupler fitting.
CAUTION: Use only the specified O-rings as they
are made of a special material for the R-134a sys-
tem. The use of any other O-rings may allow the
connection to leak intermittently during vehicle
operation.
(3) Install new O-rings on the male half of the cou-
pler fitting.
(4) Lubricate the male fitting and O-rings, and the
inside of the female fitting with clean R-134a refrig-
erant oil. Use only refrigerant oil of the type recom-
mended for the compressor in the vehicle.
(5) Fit the female half of the coupler fitting over
the male half of the fitting.
(6) Push together firmly on the two halves of the
coupler fitting until the garter spring in the cage on
the male half of the fitting snaps over the flanged
end on the female half of the fitting.
(7) Make sure that the spring-lock coupler is fully
engaged by trying to separate the two coupler halves.
This is done by pulling the refrigerant lines on either
side of the coupler away from each other.
(8) Install the secondary retaining clip over the
spring-lock coupler cage.
REFRIGERANT OIL
DESCRIPTION
The refrigerant oil used in R-134a refrigerant sys-
tems is a synthetic-based, PolyAlkylene Glycol (PAG),
wax-free lubricant. Mineral-based R-12 refrigerant
oils are not compatible with PAG oils, and should
never be introduced to an R-134a refrigerant system.
There are different PAG oils available, and each
contains a different additive package. Two different
type of A/C compressors are used in this vehicle
depending on engine application. Both compressors
are designed to use a PAG refrigerant oil. However,
the PAG oil type differs between the two compressor
Fig. 28 Refrigerant Line Spring-Lock Coupler
Disconnect
24 - 68 PLUMBINGDR
REFRIGERANT LINE COUPLER (Continued)

(2) Disconnect the refrigerant lines from the A/C
compressor. Cap open lines to prevent moisture from
entering the system.
(3) Remove the A/C compressor from the vehicle.
(4) From the suction and discharge ports on the
A/C compressor, drain the lubricant from the old A/C
compressor into a clean container.
(5) From the suction and discharge ports on the
A/C compressor, drain the lubricant from the new
A/C compressor into a clean container.
(6) Install new lubricant back into the new A/C
compressor in the amount measured from the used
compressor, plus adding any amount of lubricant lost
when the refrigerant system was reclaimed.
(7) Install the A/C compressor and connect the
refrigerant lines. Then evacuate and charge refriger-
ant system.
SERVICE PORT VALVE CORE
DESCRIPTION
A/C SERVICE PORT VALVE CORES
The A/C service port valve cores are serviceable
items. The A/C pressure transducer is mounted on
the high side service port which is located on the dis-
charge line near the A/C compressor. The low side
service port is located on the suction line near the
accumulator outlet tube.
REMOVAL - SERVICE PORT VALVE CORES
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMBING -
WARNING) and (Refer to 24 - HEATING & AIR CON-
DITIONING/PLUMBING - CAUTION).
(1) Remove the protective cap from the low side
service port as necessary.
(2) Remove the A/C pressure transducer from the
high side service port as necessary (Refer to 24 -
HEATING & AIR CONDITIONING/CONTROLS/A/C
PRESSURE TRANSDUCER - REMOVAL).
(3) Recover the refrigerant from the refrigerant
system (Refer to 24 - HEATING & AIR CONDITION-
ING/PLUMBING/REFRIGERANT - STANDARD
PROCEDURE).
(4) Using a standard Schrader-type valve core tool,
remove the valve core from the service ports as
required.
(5) Install a plug in or tape over the opened ser-
vice port(s).
INSTALLATION
(1) Lubricate the A/C service port valve core with
clean refrigerant oil prior to installation. Use only
refrigerant oil of the type recommended for the A/C
compressor in the vehicle.
(2) Remove the tape or plug from the A/C service
port.
CAUTION: A valve core that is not fully seated in
the A/C service port can result in damage to the
valve during refrigerant system evacuation and
charge. Such damage may result in a loss of sys-
tem refrigerant while uncoupling the charge adapt-
ers.
(3) Using a standard Schrader-type valve core tool,
install and tighten the replacement valve core into
the A/C service ports as required.
(4) Evacuate the refrigerant system (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
FRONT/REFRIGERANT - STANDARD PROCE-
DURE - REFRIGERANT SYSTEM EVACUATE).
(5) Charge the refrigerant system (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
FRONT/REFRIGERANT - STANDARD PROCE-
DURE - REFRIGERANT SYSTEM CHARGE).
(6) Install the A/C pressure transducer to the high
side service port as necessary (Refer to 24 - HEAT-
ING & AIR CONDITIONING/CONTROLS/A/C
PRESSURE TRANSDUCER - INSTALLATION).
(7) Install the protective cap onto the A/C service
ports as required.
SUCTION LINE
DESCRIPTION
The suction line is the refrigerant line that goes
from the evaporator outlet tube to the compressor
inlet port. The suction line for the 5.9L Diesel engine
is only serviced as an assembly with the discharge
line. The suction line has no serviceable parts except
the rubber O-rings. If the suction line is found to be
leaking or is damaged, it must be replaced.
REMOVAL
REMOVAL - 5.9L DIESEL ENGINE
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS SECTION BEFORE
PERFORMING THE FOLLOWING OPERATION (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMBING -
WARNING) and (Refer to 24 - HEATING & AIR CON-
DITIONING/PLUMBING - CAUTION).
24 - 70 PLUMBINGDR
REFRIGERANT OIL (Continued)

(1) Disconnect and isolate the battery negative
cable.
(2) Recover the refrigerant from the refrigerant
system (Refer to 24 - HEATING & AIR CONDITION-
ING/PLUMBING - STANDARD PROCEDURE -
REFRIGERANT RECOVERY).
(3) Disconnect the wire harness connector from the
A/C pressure transducer.
(4) Remove the nut that secures the discharge line
fitting to the condenser inlet port (Fig. 29).
(5) Disconnect the discharge line from the con-
denser.
(6) Remove the O-ring seal from the discharge line
fitting and discard.
(7) Install plugs in, or tape over the discharge line
fitting and condenser inlet port.
(8) Remove the bolt that secures the suction/dis-
charge line assembly to the A/C compressor.
(9) Disconnect the suction/discharge line assembly
from the A/C compressor.
(10) Remove the O-ring seals from the suction and
discharge line fittings and discard.
(11) Install plugs in, or tape over all of the opened
refrigerant line fittings and the compressor ports.(12) Remove the secondary retaining clip from the
spring-lock coupler that secures the suction line to
the accumulator outlet tube (Fig. 30).
(13) Using the proper A/C line disconnect tool, dis-
connect the suction line from the accumulator outlet
tube (Refer to 24 - HEATING & AIR CONDITION-
ING/PLUMBING/REFRIGERANT LINE COUPLER -
REMOVAL).
(14) Remove the O-ring seal from the accumulator
outlet tube fitting and discard.
(15) Install plugs in, or tape over the opened suc-
tion line and the accumulator outlet tube fitting.
(16) Remove the suction/discharge line assembly
from the engine compartment.
(17) If necessary, remove the A/C pressure trans-
ducer from the discharge line.
REMOVAL - 3.7L/4.7L AND 5.7L HEMI ENGINE
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS SECTION BEFORE
PERFORMING THE FOLLOWING OPERATION (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMBING -
WARNING) and (Refer to 24 - HEATING & AIR CON-
DITIONING/PLUMBING - CAUTION).
Fig. 29 A/C Suction Line - 5.9L Diesel Engine
1 - CONDENSER
2 - NUT
3 - LIQUID LINE
4 - NUT
5 - PRESSURE TRANSDUCER WIRE CONNECTOR
6 - A/C COMPRESSOR
7 - BOLT
8 - SUCTION/DISCHARGE LINE ASSEMBLY
Fig. 30 Suction Line - A/C Accumulator
1 - RH INNER FENDER
2 - ACCUMULATOR INLET TUBE
3 - A/C LINE SECONDARY RETAINING CLIP
4 - EVAPORATOR OUTLET TUBE
5 - BOLTS (2)
6 - ACCUMULATOR
7 - SUCTION LINE
8 - A/C LOW PRESSURE SERVICE PORT
9 - A/C LINE SECONDARY RETAINING CLIP
DRPLUMBING 24 - 71
SUCTION LINE (Continued)

(1) Disconnect and isolate the battery negative
cable.
(2) Recover the refrigerant from the refrigerant
system (Refer to 24 - HEATING & AIR CONDITION-
ING/PLUMBING - STANDARD PROCEDURE -
REFRIGERANT RECOVERY).
(3) Remove the nut that secures the suction line
fitting to the compressor inlet port (Fig. 31) or (Fig.
32), depending on application.
(4) Disconnect the suction line from the compres-
sor.
(5) Remove the O-ring seal from the suction line
fitting and discard.
(6) Install plugs in, or tape over the suction line
fitting and compressor inlet port.
(7) Remove the secondary retaining clip from the
spring-lock coupler that secures the suction line to
the accumulator outlet tube (Fig. 33).
(8) Using the proper A/C line disconnect tool, dis-
connect the suction line from the accumulator outlet
tube (Refer to 24 - HEATING & AIR CONDITION-
ING/PLUMBING/REFRIGERANT LINE COUPLER -
REMOVAL).
(9) Remove the O-ring seal from the accumulator
outlet tube fitting and discard.(10) Install plugs in, or tape over the opened suc-
tion line and the accumulator outlet tube fitting.
INSTALLATION
INSTALLATION - 5.9L DIESEL ENGINE
(1) If removed, install the A/C pressure transducer
onto the discharge line using a new O-ring seal.
Tighten the transducer securely.
(2) Position the suction/discharge line assembly
into the engine compartment.
(3) Remove the tape or plugs from the suction line
and the accumulator outlet tube fitting.
(4) Lubricate a new rubber O-ring seal with clean
refrigerant oil and install it on the accumulator out-
let tube fitting. Use only the specified O-ring as it is
made of a special material for the R-134a system.
Use only refrigerant oil of the type recommended for
the A/C compressor in the vehicle.
(5) Connect the suction line to the accumulator
outlet tube (Refer to 24 - HEATING & AIR CONDI-
TIONING/PLUMBING/REFRIGERANT LINE COU-
PLER - INSTALLATION).
(6) Install the secondary retaining clip onto the
spring-lock coupler that secures the suction line to
the accumulator outlet tube.Fig. 31 A/C Discharge Line - 3.7L Shown, 4.7L
Typical
1 - NUT
2 - FRONT UPPER CROSSMEMBER
3 - A/C CONDENSER
4 - NUT (2)
5 - SUCTION LINE
6 - A/C COMPRESSOR
7 - A/C PRESSURE TRANSDUCER
8 - WIRE HARNESS CONNECTOR
9 - A/C DISCHARGE LINE
Fig. 32 A/C Suction Line - 5.7L Hemi Engine
1 - DISCHARGE LINE
2 - NUT
3 - CONDENSER
4 - NUT
5 - SUCTION LINE
6 - A/C COMPRESSOR
7 - NUT
8 - A/C PRESSURE TRANSDUCER
24 - 72 PLUMBINGDR
SUCTION LINE (Continued)

(7) Remove the tape or plugs from the suction and
discharge line fittings and the compressor ports.
(8) Lubricate new rubber O-ring seals with clean
refrigerant oil and install them on the suction and
discharge line fittings. Use only the specified O-rings
as they are made of a special material for the R-134a
system. Use only refrigerant oil of the type recom-
mended for the A/C compressor in the vehicle.
(9) Connect the suction/discharge line assembly to
the compressor.
(10) Install and tighten the bolt that secures the
suction/discharge line assembly to the compressor.
Tighten the bolt to 28 N´m (20 ft. lbs.).
(11) Remove the tape or plugs from the discharge
line fitting and condenser inlet port.
(12) Lubricate a new rubber O-ring seal with clean
refrigerant oil and install it on the discharge line fit-
ting. Use only the specified O-ring as it is made of a
special material for the R-134a system. Use only
refrigerant oil of the type recommended for the A/C
compressor in the vehicle.
(13) Connect the discharge line to the condenser
inlet port.(14) Install and tighten the nut that secures the
discharge line fitting to the condenser. Tighten the
nut to 20 N´m (180 in. lbs.).
(15) Connect the wire harness connector to the A/C
pressure transducer.
(16) Reconnect the battery negative cable.
(17) Evacuate the refrigerant system (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM EVACUATE).
(18) Charge the refrigerant system (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM CHARGE).
INSTALLATION - 3.7L/4.7L AND 5.7L HEMI
ENGINE
(1) Position the suction line into the engine com-
partment.
(2) Remove the tape or plugs from the suction line
fitting and the compressor inlet port.
(3) Lubricate a new rubber O-ring seal with clean
refrigerant oil and install it on the suction line fit-
ting. Use only the specified O-ring as it is made of a
special material for the R-134a system. Use only
refrigerant oil of the type recommended for the A/C
compressor in the vehicle.
(4) Connect the suction line to the compressor.
(5) Install and tighten the nut that secures the
suction line to the compressor. Tighten the nut to 28
N´m (20 ft. lbs.).
(6) Remove the tape or plugs from the suction line
and the accumulator outlet tube fitting.
(7) Lubricate a new rubber O-ring seal with clean
refrigerant oil and install it on the accumulator out-
let tube fitting. Use only the specified O-ring as it is
made of a special material for the R-134a system.
Use only refrigerant oil of the type recommended for
the A/C compressor in the vehicle.
(8) Connect the suction line to the accumulator
outlet tube (Refer to 24 - HEATING & AIR CONDI-
TIONING/PLUMBING/REFRIGERANT LINE COU-
PLER - INSTALLATION).
(9) Install the secondary retaining clip onto the
spring-lock coupler that secures the suction line to
the accumulator outlet tube.
(10) Reconnect the battery negative cable.
(11) Evacuate the refrigerant system (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM EVACUATE).
(12) Charge the refrigerant system (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM CHARGE).
Fig. 33 A/C Accumulator - Typical
1 - RH INNER FENDER
2 - ACCUMULATOR INLET TUBE
3 - A/C LINE SECONDARY RETAINING CLIP
4 - EVAPORATOR OUTLET TUBE
5 - BOLTS (2)
6 - ACCUMULATOR
7 - SUCTION LINE
8 - A/C LOW PRESSURE SERVICE PORT
9 - A/C LINE SECONDARY RETAINING CLIP
DRPLUMBING 24 - 73
SUCTION LINE (Continued)

EMISSIONS CONTROL
TABLE OF CONTENTS
page page
EMISSIONS CONTROL
DESCRIPTION
DESCRIPTION - STATE DISPLAY TEST
MODE...............................1
DESCRIPTION - CIRCUIT ACTUATION TEST
MODE...............................1
DESCRIPTION - DIAGNOSTIC TROUBLE
CODES..............................1
DESCRIPTION - TASK MANAGER..........1DESCRIPTION - MONITORED SYSTEMS....2
DESCRIPTION - TRIP DEFINITION.........4
DESCRIPTION - COMPONENT MONITORS . . 4
OPERATION
OPERATION..........................5
OPERATION - TASK MANAGER...........5
OPERATION - NON-MONITORED CIRCUITS . . 8
EVAPORATIVE EMISSIONS................10
EMISSIONS CONTROL
DESCRIPTION
DESCRIPTION - STATE DISPLAY TEST MODE
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. Connect
the DRB scan tool to the data link connector and
access the state display screen. Then access either
State Display Inputs and Outputs or State Display
Sensors.
DESCRIPTION - CIRCUIT ACTUATION TEST
MODE
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. Connect the DRB scan tool to the data link
connector and access the Actuators screen.
DESCRIPTION - DIAGNOSTIC TROUBLE CODES
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.
BULB CHECK
Each time the ignition key is turned to the ON
position, the malfunction indicator (check engine)
lamp on the instrument panel should illuminate for
approximately 2 seconds then go out. This is done for
a bulb check.
OBTAINING DTC'S USING DRB SCAN TOOL
(1) Obtain the applicable Powertrain Diagnostic
Manual.
(2) Obtain the DRB Scan Tool.
(3) Connect the DRB Scan Tool to the data link
(diagnostic) connector. This connector is located in
the passenger compartment; at the lower edge of
instrument panel; near the steering column.
(4) Turn the ignition switch on and access the
ªRead Faultº screen.
(5) Record all the DTC's and ªfreeze frameº infor-
mation shown on the DRB scan tool.
(6) To erase DTC's, use the ªErase Trouble Codeº
data screen on the DRB scan tool.Do not erase any
DTC's until problems have been investigated
and repairs have been performed.
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 call the 'Task Manager'.
DREMISSIONS CONTROL 25 - 1

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 richerthan 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-
tive 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.
25 - 2 EMISSIONS CONTROLDR
EMISSIONS CONTROL (Continued)

Immediately after a cold start, between predeter-
mined temperature thresholds limits, the three port
solenoid is briefly energized. This initializes the
pump by drawing air into the pump cavity and also
closes the vent seal. During non test conditions the
vent seal is held open by the pump diaphragm
assembly which pushes it open at the full travel posi-
tion. The vent seal will remain closed while the
pump is cycling due to the reed switch triggering of
the three port solenoid that prevents the diaphragm
assembly from reaching full travel. After the brief
initialization period, the solenoid is de-energized
allowing atmospheric pressure to enter the pump
cavity, thus permitting the spring to drive the dia-
phragm which forces air out of the pump cavity and
into the vent system. When the solenoid is energized
and de energized, the cycle is repeated creating flow
in typical diaphragm pump fashion. The pump is con-
trolled in 2 modes:
Pump Mode: The pump is cycled at a fixed rate to
achieve a rapid pressure build in order to shorten the
overall test length.
Test Mode: The solenoid is energized with a fixed
duration pulse. Subsequent fixed pulses occur when
the diaphragm reaches the Switch closure point.
The spring in the pump is set so that the system
will achieve an equalized pressure of about 7.5º H20.
The cycle rate of pump strokes is quite rapid as the
system begins to pump up to this pressure. As the
pressure increases, the cycle rate starts to drop off. If
there is no leak in the system, the pump would even-
tually stop pumping at the equalized pressure. If
there is a leak, it will continue to pump at a rate rep-
resentative of the flow characteristic of the size of the
leak. From this information we can determine if the
leak is larger than the required detection limit (cur-
rently set at .040º orifice by CARB). If a leak is
revealed during the leak test portion of the test, the
test is terminated at the end of the test mode and no
further system checks will be performed.
After passing the leak detection phase of the test,
system pressure is maintained by turning on the
LDP's solenoid until the purge system is activated.
Purge activation in effect creates a leak. The cycle
rate is again interrogated and when it increases due
to the flow through the purge system, the leak check
portion of the diagnostic is complete.
The canister vent valve will unseal the system
after completion of the test sequence as the pump
diaphragm assembly moves to the full travel position.
Evaporative system functionality will be verified by
using the stricter evap purge flow monitor. At an
appropriate warm idle the LDP will be energized to
seal the canister vent. The purge flow will be clocked
up from some small value in an attempt to see a
shift in the 02 control system. If fuel vapor, indicatedby a shift in the 02 control, is present the test is
passed. If not, it is assumed that the purge system is
not functioning in some respect. The LDP is again
turned off and the test is ended.
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 of 14.7 to 1. This is done by making
short term corrections in the fuel injector pulse width
based on the O2S sensor 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 fuel-air ratio with the O2S sensor (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 emis-
sions test. If a malfunction occurs such that the PCM
cannot maintain the optimum A/F ratio, then the
MIL will be illuminated.
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. 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'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
DREMISSIONS CONTROL 25 - 3
EMISSIONS CONTROL (Continued)

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, it
depends 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 with-
out an associated limp-in will take two trips to illu-
minate the MIL.
25 - 4 EMISSIONS CONTROLDR
EMISSIONS CONTROL (Continued)