2001 DODGE RAM ABS

STATIONARY GLASS
TABLE OF CONTENTS
page page
STATIONARY GLASS
DESCRIPTION..........................145
OPERATION............................145
BACKLITE
REMOVAL.............................145
INSTALLATION..........................145
BACKLITE LATCH AND KEEPER
REMOVAL.............................146
INSTALLATION..........................146
BACKLITE VENT GLASS
REMOVAL.............................147INSTALLATION..........................147
WINDSHIELD
DESCRIPTION..........................148
REMOVAL.............................148
INSTALLATION..........................148
QUARTER WINDOW
REMOVAL.............................151
INSTALLATION..........................151
STATIONARY GLASS
DESCRIPTION
Windshields are made of two pieces of glass with a
plastic inner layer. Windshields and selected station-
ary glass are structural members of the vehicle. The
windshield glass is bonded to the windshield frame
with urethane adhesive.
OPERATION
Windshields and other stationary glass protect the
occupants from the effects of the elements. Wind-
shields are also used to retain some airbags in posi-
tion during deployment. Urethane bonded glass is
difficult to salvage during removal. The urethane
bonding is difficult to cut or clean from any surface.
Before removing the glass, check the availability of
replacement components.
BACKLITE
REMOVAL
It is difficult to salvage the backlite during the
removal operation. The backlite is part of the struc-
tural support for the roof. The urethane bonding
used to secure the glass to the fence is difficult to cut
or clean from any surface. Since the molding is set in
urethane, it is unlikely it would be salvaged. Before
removing the backlite, check the availability from the
parts supplier.
The backlite is attached to the window frame with
urethane adhesive. The urethane adhesive is applied
cold and seals the surface area between the window
opening and the glass. The primer adheres the ure-
thane adhesive to the backlite.(1) Roll down door glass.
(2) Remove headliner. (Refer to 23 - BODY/INTE-
RIOR/HEADLINER - REMOVAL).
(3) Remove rear closer panel trim. (Refer to 23 -
BODY/INTERIOR/REAR CLOSURE PANEL TRIM -
REMOVAL).
(4) Bend backlite retaining tabs (Fig. 1) inward
against glass.
(5) Using a suitable pneumatic knife from inside
the vehicle, cut urethane holding backlite frame to
opening fence.
(6) Separate glass from vehicle.
INSTALLATION
(1) Clean urethane adhesive from around backlite
opening fence.
Fig. 1 Backlite Tabs
1 - BACKLITE
2-TAB
BR/BESTATIONARY GLASS 23 - 145

(2) If necessary, apply black-out primer to outer
edge of replacement backlite frame.
(3) If black-out primer was pre-applied on backlite,
clean bonding surface with Isopropyl alcohol and
clean lint free cloth. Allow 3 minutes for drying time.
(4) Apply black-out primer to backlite opening
fence.
(5) Apply a 13 mm (0.5 in.) bead of urethane
around the perimeter of the window frame bonding
surface (Fig. 2).
(6) Set glass on lower fence and move glass for-
ward into opening (Fig. 3).
(7) Firmly push glass against rear window glass
opening fence.
(8) Bend tabs around edges of backlite opening
fence to retain glass.
(9) Clean excess urethane from exterior with
MOPAR, Super Clean or equivalent.
(10) Allow urethane to cure at least 24 hours (full
cure is 72 hours).
(11) Water test to verify repair before returning
vehicle to service.
(12) Install rear closer panel trim. (Refer to 23 -
BODY/INTERIOR/REAR CLOSURE PANEL TRIM -
INSTALLATION).
(13) Install the headliner. (Refer to 23 - BODY/IN-
TERIOR/HEADLINER - INSTALLATION).
BACKLITE LATCH AND
KEEPER
REMOVAL
(1) Disengage latch and keeper.
(2) Remove latch/keeper screws.
(3) Separate Latch/keeper from glass panel.
INSTALLATION
(1) Position Latch/keeper on glass panel.
(2) Install screws. Tighten the screws with 1.5 N´m
(15 in. lbs.) torque.
(3) Engage latch and keeper to verify operation.
Fig. 2 Urethane Adhesive Application
1 - WINDOW FRAME
2 - GLASS
3 - RETAINER TAB
4 - URETHANE ADHESIVE
Fig. 3 Backlite Installation
1 - BACKLITE
23 - 146 STATIONARY GLASSBR/BE
BACKLITE (Continued)

heated air. This air conditioning system uses a fixed ori-
fice tube in the middle of the liquid line to meter refrig-
erant flow to the evaporator coil. To maintain minimum
evaporator temperature and prevent evaporator freez-
ing, the a/c low pressure switch on the accumulator
cycles the compressor clutch.
OPERATION - REFRIGERANT SYSTEM SERVICE
PORT
The high pressure service port is located on the liq-
uid line between the condenser and the evaporator,
near the front of the engine compartment. The low
pressure service port is located on the suction line,
near the accumulator outlet.
Each of the service ports has a threaded plastic
protective cap installed over it from the factory. After
servicing the refrigerant system, always reinstall
both of the service port caps.
DIAGNOSIS AND TESTING - A/C
PERFORMANCE
The air conditioning system is designed to provide
the passenger compartment with low temperature
and low humidity air. The evaporator, located in the
HVAC housing on the dash panel below the instru-
ment panel, is cooled to temperatures near the freez-
ing point. As warm damp air passes through the
cooled evaporator, the air transfers its heat to the
refrigerant in the evaporator tubes and the moisture
in the air condenses on the evaporator fins. During
periods of high heat and humidity, an air condition-
ing system will be more effective in the recirculation
mode (Max-A/C). With the system in the recirculation
mode, only air from the passenger compartment
passes through the evaporator. As the passenger com-
partment air dehumidifies, the air conditioning sys-
tem performance levels improve.
Humidity has an important bearing on the temper-
ature of the air delivered to the interior of the vehi-
cle. It is important to understand the effect that
humidity has on the performance of the air condition-
ing system. When humidity is high, the evaporator
has to perform a double duty. It must lower the air
temperature, and it must lower the temperature of
the moisture in the air that condenses on the evapo-
rator fins. Condensing the moisture in the air trans-
fers heat energy into the evaporator fins and tubing.
This reduces the amount of heat the evaporator can
absorb from the air. High humidity greatly reduces
the ability of the evaporator to lower the temperature
of the air.
However, evaporator capacity used to reduce the
amount of moisture in the air is not wasted. Wring-
ing some of the moisture out of the air entering the
vehicle adds to the comfort of the passengers.
Although, an owner may expect too much from theirair conditioning system on humid days. A perfor-
mance test is the best way to determine whether the
system is performing up to standard. This test also
provides valuable clues as to the possible cause of
trouble with the air conditioning system.
Before proceeding, (Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING - WARNING) and
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - CAUTION). The air temperature in
the test room and in the vehicle must be a minimum
of 21É C (70É F) for this test.
(1)
Connect a tachometer and a manifold gauge set.
(2) Set the a/c heater mode control switch knob to
the recirculation mode (Max-A/C) position, the tem-
perature control knob to the full cool position, and
the blower motor switch to the highest speed posi-
tion.
(3) Start the engine and hold the idle speed at
1,000 rpm with the compressor clutch engaged. If the
compressor clutch does not engage, (Refer to 24 -
HEATING & AIR CONDITIONING/CONTROLS/A/C
COMPRESSOR CLUTCH COIL - DIAGNOSIS AND
TESTING).
(4) The engine should be at operating temperature.
The doors and windows must be closed and the hood
must be mostly closed.
(5)
Insert a thermometer in the driver side center
A/C (panel) outlet. Operate the engine for five minutes.
(6) The compressor clutch may cycle, depending
upon the ambient temperature and humidity. If the
clutch cycles, unplug the a/c low pressure switch wire
harness connector from the switch located on the
accumulator (Fig. 2). Place a jumper wire between
the two cavities of the a/c low pressure switch wire
harness connector.
Fig. 2 A/C LOW PRESSURE SWITCH
1 - A/C LOW PRESSURE SWITCH
2 - ACCUMULATOR
24 - 2 HEATING & AIR CONDITIONINGBR/BE
HEATING & AIR CONDITIONING (Continued)

CAUTION:
Liquid refrigerant is corrosive to metal surfaces.
Follow the operating instructions supplied with the
service equipment being used.
Never add R-12 to a refrigerant system designed to
use R-134a. Damage to the system will result.
R-12 refrigerant oil must not be mixed with R-134a
refrigerant oil. They are not compatible.
Do not use R-12 equipment or parts on the R-134a
system. Damage to the system will result.
Do not overcharge the refrigerant system. This will
cause excessive compressor head pressure and
can cause noise and system failure.
Recover the refrigerant before opening any fitting
or connection. Open the fittings with caution, even
after the system has been discharged. Never open
or loosen a connection before recovering the refrig-
erant.
Do not remove the secondary retention clip from
any spring-lock coupler connection while the refrig-
erant system is under pressure. Recover the refrig-
erant before removing the secondary retention clip.
Open the fittings with caution, even after the sys-
tem has been discharged. Never open or loosen a
connection before recovering the refrigerant.
The refrigerant system must always be evacuated
before charging.
Do not open the refrigerant system or uncap a
replacement component until you are ready to ser-
vice the system. This will prevent contamination in
the system.
Before disconnecting a component, clean the out-
side of the fittings thoroughly to prevent contami-
nation from entering the refrigerant system.
Immediately after disconnecting a component from
the refrigerant system, seal the open fittings with a
cap or plug.
Before connecting an open refrigerant fitting,
always install a new seal or gasket. Coat the fitting
and seal with clean refrigerant oil before connect-
ing.
Do not remove the sealing caps from a replacement
component until it is to be installed.
When installing a refrigerant line, avoid sharp
bends that may restrict refrigerant flow. Position the
refrigerant lines away from exhaust system compo-
nents or any sharp edges, which may damage the
line.
Tighten refrigerant fittings only to the specified
torque. The aluminum fittings used in the refriger-
ant system will not tolerate overtightening.
When disconnecting a refrigerant fitting, use a
wrench on both halves of the fitting. This will pre-
vent twisting of the refrigerant lines or tubes.
Refrigerant oil will absorb moisture from the atmo-
sphere if left uncapped. Do not open a container ofrefrigerant oil until you are ready to use it. Replace
the cap on the oil container immediately after using.
Store refrigerant oil only in a clean, airtight, and
moisture-free container.
Keep service tools and the work area clean. Con-
tamination of the refrigerant system through care-
less work habits must be avoided.
CAUTION - REFRIGERANT HOSES/LINES/
TUBES PRECAUTIONS
Kinks or sharp bends in the refrigerant plumbing
will reduce the capacity of the entire system. High
pressures are produced in the system when it is oper-
ating. Extreme care must be exercised to make sure
that all refrigerant system connections are pressure
tight.
A good rule for the flexible hose refrigerant lines is
to keep the radius of all bends at least ten times the
diameter of the hose. Sharp bends will reduce the
flow of refrigerant. The flexible hose lines should be
routed so they are at least 80 millimeters (3 inches)
from the exhaust manifold. It is a good practice to
inspect all flexible refrigerant system hose lines at
least once a year to make sure they are in good con-
dition and properly routed.
There are two types of refrigerant fittings:
²All fittings with O-rings need to be coated with
refrigerant oil before installation. Use only O-rings
that are the correct size and approved for use with
R-134a refrigerant. Failure to do so may result in a
leak.
²Unified plumbing connections with gaskets can-
not be serviced with O-rings. The gaskets are not
reusable and new gaskets do not require lubrication
before installing.
Using the proper tools when making a refrigerant
plumbing connection is very important. Improper
tools or improper use of the tools can damage the
refrigerant fittings. Always use two wrenches when
loosening or tightening tube fittings. Use one wrench
to hold one side of the connection stationary, while
loosening or tightening the other side of the connec-
tion with a second wrench.
The refrigerant must be recovered completely from
the system before opening any fitting or connection.
Open the fittings with caution, even after the refrig-
erant has been recovered. If any pressure is noticed
as a fitting is loosened, tighten the fitting and
recover the refrigerant from the system again.
Do not discharge refrigerant into the atmosphere.
Use an R-134a refrigerant recovery/recycling device
that meets SAE Standard J2210.
24 - 42 PLUMBINGBR/BE
PLUMBING (Continued)

compressor is engaged and circulating refrigerant
through the evaporator coil tubes.
OPERATION
Refrigerant enters the evaporator from the fixed
orifice tube as a low-temperature, low-pressure liq-
uid. As air flows over the fins of the evaporator, the
humidity in the air condenses on the fins, and the
heat from the air is absorbed by the refrigerant. Heat
absorption causes the refrigerant to boil and vapor-
ize. The refrigerant becomes a low-pressure gas when
it leaves the evaporator.
The evaporator coil cannot be repaired and, if
faulty or damaged, it must be replaced.
REMOVAL
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) (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - CAUTION)
(1) Remove the HVAC housing from the vehicle,
and disassemble the housing halves. (Refer to 24 -
HEATING & AIR CONDITIONING/DISTRIBUTION/
HVAC HOUSING - REMOVAL) (Refer to 24 - HEAT-
ING & AIR CONDITIONING/DISTRIBUTION/HVAC
HOUSING - DISASSEMBLY)
(2) Lift the a/c evaporator out of the HVAC hous-
ing (Fig. 11).
INSTALLATION
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) (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - CAUTION)(Refer to
24 - HEATING & AIR CONDITIONING/PLUMBING -
CAUTION - REFRIGERANT HOSES/LINES/TUBES
PRECAUTIONS)
(1) Insert the evaporator coil into the bottom of the
HVAC housing.
(2) Reassemble and reinstall the HVAC housing in
the vehicle. (Refer to 24 - HEATING & AIR CONDI-
TIONING/DISTRIBUTION/HVAC HOUSING -
ASSEMBLY) (Refer to 24 - HEATING & AIR CON-
DITIONING/DISTRIBUTION/HVAC HOUSING -
INSTALLATION)
NOTE: If the evaporator is replaced, add 60 millili-
ters (2 fluid ounces) of refrigerant oil to the refrig-
erant system.
A/C ORIFICE TUBE
DESCRIPTION
The fixed orifice tube is installed in the liquid line
between the outlet of the condenser and the inlet of
the evaporator. The fixed orifice tube is only serviced
as an integral part of the liquid line.
OPERATION
The inlet end of the fixed orifice tube has a nylon
mesh filter screen, which filters the refrigerant and
helps to reduce the potential for blockage of the
metering orifice by refrigerant system contaminants
(Fig. 12). The outlet end of the tube has a nylon
mesh diffuser screen. The O-rings on the plastic body
of the fixed orifice tube seal the tube to the inside of
the liquid line and prevent the refrigerant from
bypassing the fixed metering orifice.
The fixed orifice tube is used to meter the flow of
liquid refrigerant into the evaporator coil. The high-
pressure liquid refrigerant from the condenser
expands into a low-pressure liquid as it passes
through the metering orifice and diffuser screen of
the fixed orifice tube.
The fixed orifice tube cannot be repaired and, if
faulty or plugged, the liquid line assembly must be
replaced.
Fig. 11 A/C EVAPORATOR LOCATION IN HVAC
HOUSING (UPSIDE DOWN)
1 - EVAPORATOR LOCATION
2 - BOTTOM HALF OF HVAC HOUSING
3 - TOP HALF OF HVAC HOUSING
BR/BEPLUMBING 24 - 53
A/C EVAPORATOR (Continued)

DIAGNOSIS AND TESTING - FIXED ORIFICE
TUBE
The fixed orifice tube can be checked for proper
operation using the following procedure. However,
the fixed orifice tube is only serviced as a part of the
liquid line unit. If the results of this test indicate
that the fixed orifice tube is obstructed or missing,
the entire liquid line unit must be replaced.
WARNING: THE LIQUID LINE BETWEEN THE CON-
DENSER OUTLET AND THE FIXED ORIFICE TUBE
CAN BECOME HOT ENOUGH TO BURN THE SKIN.
USE EXTREME CAUTION WHEN PERFORMING THE
FOLLOWING TEST.
(1) Confirm that the refrigerant system is properly
charged. (Refer to 24 - HEATING & AIR CONDI-
TIONING - DIAGNOSIS AND TESTING - A/C PER-
FORMANCE)
(2) Start the engine. Turn on the air conditioning
system and confirm that the compressor clutch is
engaged.
(3) Allow the air conditioning system to operate for
five minutes.
(4) Lightly and cautiously touch the liquid line
near the condenser outlet at the front of the engine
compartment. The liquid line should be hot to the
touch.
(5) Touch the liquid line near the evaporator inlet
at the rear of the engine compartment. The liquid
line should be cold to the touch.
(6) If there is a distinct temperature differential
between the two ends of the liquid line, the orifice
tube is in good condition. If there is little or no
detectable temperature differential between the two
ends of the liquid line, the orifice tube is obstructed
or missing and the liquid line must be replaced.
REMOVAL
The fixed orifice tube is located in the liquid line,
between the condenser and the evaporator coil. If the
fixed orifice tube is faulty or plugged, the liquid line
assembly must be replaced. (Refer to 24 - HEATING
& AIR CONDITIONING/PLUMBING/LIQUID LINE
- REMOVAL)
ACCUMULATOR
DESCRIPTION
The accumulator is mounted in the engine com-
partment between the a/c evaporator outlet tube and
the compressor inlet.
OPERATION
Refrigerant enters the accumulator canister as a
low pressure vapor through the inlet tube. Any liq-
uid, oil-laden refrigerant falls to the bottom of the
canister, which acts as a separator. A desiccant bag is
mounted inside the accumulator canister to absorb
any moisture which may have entered and become
trapped within the refrigerant system (Fig. 13).
REMOVAL
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) (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - CAUTION)
(1) Disconnect and isolate the battery negative
cable.
(2) Recover the refrigerant from the refrigerant
system. (Refer to 24 - HEATING & AIR CONDI-
TIONING/PLUMBING - STANDARD PROCEDURE -
REFRIGERANT RECOVERY)
(3) Remove the a/c low pressure switch from the
accumulator. (Refer to 24 - HEATING & AIR CON-
DITIONING/CONTROLS/A/C LOW PRESSURE
SWITCH - REMOVAL)
(4) Loosen the screw that secures the accumulator
retaining band to the support bracket on the dash
panel (Fig. 20).
(5) Disconnect the suction line refrigerant line fit-
ting from the accumulator outlet. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - A/C LINE COUPLERS)
Install plugs in, or tape over all of the opened refrig-
erant line fittings.
(6) Disconnect the accumulator inlet refrigerant
line fitting from the evaporator outlet. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
Fig. 12 FIXED ORIFICE TUBE - TYPICAL
1 - DIFFUSER SCREEN
2 - ªOº RINGS
3 - INLET FILTER SCREEN
4 - ORIFICE
24 - 54 PLUMBINGBR/BE
A/C ORIFICE TUBE (Continued)

more information on the engine cooling system, the
engine coolant and the heater hoses.
REMOVAL
(1) Remove the HVAC housing from the vehicle.
(Refer to 24 - HEATING & AIR CONDITIONING/
DISTRIBUTION/HVAC HOUSING - REMOVAL)
(2) Remove the screws and retainers that secure
the heater core to the HVAC housing.
(3) Lift the heater core straight up and out of the
heater-A/C housing (Fig. 14).
INSTALLATION
(1) Lower the heater core into the HVAC housing.
(2) Position the retainers over the heater core
tubes. Install and tighten the screws that secure the
heater core and retainers to the HVAC housing.
Tighten the screws to 2.2 N´m (20 in. lbs.).
(3) Reinstall the HVAC housing in the vehicle.
(Refer to 24 - HEATING & AIR CONDITIONING/
DISTRIBUTION/HVAC HOUSING - INSTALLA-
TION)
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 also
labels 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 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. The SD7H15
compressor used in this vehicle is designed to use an
SP-20 PAG refrigerant oil. Use only refrigerant oil of
this same type to service the refrigerant system.
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
Fig. 14 HEATER CORE REMOVE/INSTALL
1 - HEATER CORE LINES
2 - HEATER CORE
24 - 56 PLUMBINGBR/BE
HEATER CORE (Continued)

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, indicated
by 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. 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'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
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.
BR/BEEMISSIONS CONTROL 25 - 17
EMISSIONS CONTROL (Continued)