1998 DODGE RAM 1500 air condition

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)

designs. Useonlyrefrigerant oil of the same type as
recommended to service the refrigerant system
(always refer to the specification tagincluded
with the replacement A/C compressor or the under-
hood A/C system specification tag).
OPERATION
After performing any refrigerant recovery or recy-
cling operation, always replenish the refrigerant sys-
tem with the same amount of the recommended
refrigerant oil as was removed. Too little refrigerant
oil can cause compressor damage, and too much can
reduce air conditioning system performance.
PAG refrigerant oil is much more hygroscopic than
mineral oil, and will absorb any moisture it comes
into contact with, even moisture in the air. The PAG
oil container should always be kept tightly capped
until it is ready to be used. After use, recap the oil
container immediately to prevent moisture contami-
nation.
STANDARD PROCEDURE - REFRIGERANT OIL
LEVEL
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).
CAUTION: The refrigerant oil in the R-134a A/C sys-
tem is unique depending on the A/C compressor
used. Use only PAG oils that are designed to work
with R-134a refrigerant and the A/C compressor in
the vehicle. Always refer to the underhood A/C Sys-
tem Specification Label for the correct oil designa-
tion.
It is important to have the correct amount of lubri-
cant in the A/C refrigerant system to ensure proper
lubrication of the A/C compressor. Too little lubricant
will result in damage to the compressor. Too much
lubricant will reduce the cooling capacity of the A/C
system and consequently result in higher discharge
air temperatures.
The lubricant used in the compressor is polyalka-
lene glycol PAG lubricant. Only the refrigerant lubri-
cant approved for use with this vehicle should be
used to service the system. Do not use any other
lubricant. The lubricant container should be kept
tightly capped until it is ready for use. Refrigerant
lubricant will quickly absorb any moisture it comes
in contact with.
It will not be necessary to check the oil level in the
A/C compressor or to add oil, unless there has beenan oil loss. An oil loss may occur due to component
replacement, or a rupture or leak from a refrigerant
line, connector fitting, component or component seal.
If a leak occurs, add 30 milliliters (1 fluid ounce) of
the recommended refrigerant oil to the refrigerant
system after the repair has been made. Refrigerant
oil loss will be evident at the leak point by the pres-
ence of a wet, shiny surface around the leak.
COMPONENT REFRIGERANT OIL LEVEL CHECK
When an air conditioning system is first assembled
at the factory, all components (except the A/C com-
pressor) are refrigerant oil free. After the refrigerant
system has been charged with (R-134a) refrigerant
and operated, the oil in the A/C compressor is dis-
persed through the lines and components. The A/C
evaporator, A/C condenser, and accumulator will
retain a significant amount of oil. Refer to the A/C
Component Refrigerant Oil Capacities table. When a
component is replaced, the specified amount of refrig-
erant oil must be added. When a new A/C compressor
is being installed, drain the lubricant from the used
compressor, measure the amount drained and discard
the used lubricant. Drain the lubricant from the new
A/C compressor into a clean container. Return the
amount of lubricant measured from the used com-
pressor, plus the amount reclaimed from the system
back into the new A/C compressor. When a line or
component has ruptured and oil has escaped, the
accumulator must be replaced along with the rup-
tured component.
A/C COMPONENT REFRIGERANT OIL
CAPACITIES
Component ml. oz.
Total System Fill 180 6
Accumulator 60 2
Condenser 30 1
Evaporator 60 2
Compressor Drain and measure
the oil from the old
compressor - see
text.
COMPRESSOR REFRIGERANT OIL LEVEL CHECK
NOTE: Most reclaim/recycling equipment will mea-
sure the lubricant being removed during recovery.
This amount of lubricant should be added back into
the system. Refer to the reclaim/recycling equip-
ment manufacturers instructions.
(1) Recover the refrigerant from the system.
DRPLUMBING 24 - 69
REFRIGERANT OIL (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

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)