torque CHRYSLER VOYAGER 1996 Service Manual

(2) Perform the HVAC control Calibration Diagnos-
tic and Cooldown test.
SIDE WINDOW DEMISTER DUCTS
LEFT SIDE
The LEFT side window demister duct is a two
piece design. The left side has a long duct that
attaches to an intermediate duct and then to the dis-
tribution housing. The duct is located on top of the
instrument panel. To service the duct, remove the I/P
cover and remove duct retainers/fasteners. (Fig. 59).
RIGHT SIDE
The demister duct on the right side is a one piece
design. It is one long duct that attaches to the distri-
bution housing. The duct is located on top of the
instrument panel and it is not serviceable (Fig. 60).
SUCTION LINE
REMOVAL
(1) Disconnect the battery negative cable.
(2) Recover A/C system refrigerant.
(3) Remove the accessory drive belt.
(4) Remove upper generator bracket.
(5) Remove ground wire at dash panel.
(6) Remove the nut retaining the refrigerant line
sealing plate to the expansion valve (Fig. 39).
(7) Remove the stud from the expansion valve (Fig.
40).
(8) Remove suction line from expansion valve.
(9) Remove suction line mounting nut at compres-
sor (Fig. 61).
(10) Remove suction line mounting bracket.
(11) Remove suction line.
INSTALLATION
For installation, reverse the above procedures.
²Install the stud to the evaporator sealing plate
and tighten 7 to 11 N´m (64 to 96 in. lbs.) torque.
²Install new O-rings.
Fig. 58 Mode Door Actuator
Fig. 59 Left Side Demister Duct
Fig. 60 Right Side Demister Duct
Fig. 61 Suction Line At Compressor
NSHEATING AND AIR CONDITIONING 24 - 33
REMOVAL AND INSTALLATION (Continued)

EVAPORATOR AND EXPANSION VALVE
NOTE: Special effort must be used to keep all
R-134a system components moisture-free. Moisture
in the oil is very difficult to remove and will cause a
reliability problem with the compressor.
REMOVAL
WARNING: THE REFRIGERANT SYSTEM MUST BE
EMPTY BEFORE PERFORMING THE FOLLOWING
OPERATION. THE ENGINE COOLING SYSTEM
MUST ALSO BE RELIEVED OF ALL PRESSURE.
(1) Remove right quarter trim panel and D-pillar
trim. Refer to Group 23, Body.
(2) Remove fan A/C distribution duct.
(3) Remove rear A/C unit.
(4) Remove blower scroll.
(5) Remove evaporator cover (Fig. 12).
(6) Remove the nut that mounts the refrigerant
plumbing block to the expansion valve (Fig. 13).
(7) Carefully pull the evaporator and expansion
valve straight out of unit (Fig. 14). Do not scratch
the sealing surfaces with the plumbing extension
tube pilots.
(8) Remove and discard the O-rings between the
plumbing extension and the expansion valve.
(9) Cover the plumbing extension sealing surface
to prevent contamination.
(10) Bring evaporator and expansion valve to a
clean work space.
(11) Remove two 1/4-20 Torx Head screws.
(12) Remove expansion valve.
(13) Measure and record the amount of residual oil
from the removed evaporator.
INSTALLATION
(1) Replace the O-rings.(2) Hold expansion valve against evaporator seal-
ing plate (do not scratch the sealing surface). Install
two screws and tighten to 1163 N´m (100630 inch
pounds) torque.
Fig. 11 Rear Heat-A/C UnitFig. 12 Evaporator Cover
Fig. 13 Expansion Valve
Fig. 14 Evaporator Removal
24 - 44 HEATING AND AIR CONDITIONINGNS
REMOVAL AND INSTALLATION (Continued)

CAUTION: Do not damage the evaporator insulation
liner during installation.
(3) Carefully install the evaporator and expansion
valve straight into the unit. Do not scratch the seal-
ing surfaces with the plumbing extension tube pilots.
(4) Determine the amount of old refrigerant oil
drained from the evaporator. Add this amount (of
clean refrigerant oil) back into the system.
(5) Carefully align the expansion valve onto the
pilot tubes of the plumbing extension (do not scratch
the sealing surface). Install the bolt through the
plumbing plate into the unit sealing plate. Tighten
bolts to 2363 N´m (200630 inch pounds) torque.
(6) Install evaporator cover and blower scroll.
(7) Install quarter trim panel, evacuate/charge sys-
tem, and perform the performance test.
REAR AIR CONDITIONING LINES
WARNING: THE REFRIGERATION SYSTEM MUST
BE COMPLETELY EMPTY BEFORE PROCEEDING
WITH THIS OPERATION.
REMOVAL
(1) Hoist vehicle
(2) Remove compression fittings to the suction and
liquid lines located on the right, outboard side of the
underbody, rearward of the front crossmember. (Fig.
2)
(3) remove (1) bolt securing a/c lines to block
located on the right, outboard side of the underbody,
rearward of the rear wheel and tire. (Fig. 5)
(4) Remove (3) straps securing underbody lines.
(Fig. 1)
(5) Separate and remove a/c lines from vehicle.
INSTALLATION
(1) Before installation, replace all O-rings and gas-
kets. Coat all sealing surfaces with approved wax-
free refrigerant oil. Then, reverse the above
procedures.
(2) Evacuate and recharge system.
REAR HEATER A/C AIR OUTLETS
REMOVAL
Separate barrel from bezel by pulling outward.
INSTALLATION
For installation, push the outlet firmly into the
opening until it locks into place.
REAR HEATER-A/C AUXILIARY CONDENSER
If vehicle is equipped with a 3.3L or 3.8L engine
with rear heater and air conditioning, it will be
equipped with an auxiliary condenser. The auxiliarycondenser is mounted on the primary condenser in
front of the radiator. Both condenser must be
removed as an assembly and then separated.
WARNING: THE REFRIGERATION SYSTEM MUST
BE COMPLETELY EMPTY BEFORE PROCEEDING
WITH THIS OPERATION.
NOTE: Special effort must be used to keep all
R-134a system components moisture-free. Moisture
in the oil is very difficult to remove and will cause a
reliability problem with the compressor.
The condenser assembly must first be removed
from vehicle. Refer to CONDENSER ASSEMBLY
removal and installation in this section for service
procedures.
REMOVAL
(1) After condenser assembly removal, place on
bench for disassembly.
(2) Remove (1) bolt to liquid line on auxiliary con-
denser.
(3) Remove (4) attaching bolts and separate auxil-
iary from primary condenser. (Fig. 15)
INSTALLATION
(1) Before installation, replace all O-rings and gas-
kets. Coat all sealing surfaces with approved wax-
free refrigerant oil. Then, reverse the above
procedures.
(2) Evacuate and recharge system.
Fig. 15 3.3L/3.8L REAR HEAT-A/C AUXILIARY
CONDENSER
NSHEATING AND AIR CONDITIONING 24 - 45
REMOVAL AND INSTALLATION (Continued)

(2) Hand-start the stud into the expansion valve
and torque to7-11N´m(64-96in.lbs.).
(3) Carefully install the expansion valve to the
sealing plate. Install the two screws and tighten 8 to
14 N´m (70 to 130 in. lbs.) torque.
(4) Carefully install the refrigerant lines and seal-
ing plate to the expansion valve. Install the nut and
tighten 20 to 26 N´m (170 to 230 in. lbs.) torque.
(5) Install the ground wire at dash panel.
(6) Pull generator back into the proper position for
bracket mounting.
(7) Install generator field wire connector.
(8) Install the upper generator bracket.
(9) Install accessory drive belt.
(10) Evacuate and recharge system.
(11) After expansion valve is installed, the system
is charged, and leaks have checked repeat the A/C
performance check.
FILTER-DRIER ASSEMBLY
REMOVAL
WARNING: THE REFRIGERATION SYSTEM MUST
BE COMPLETELY EMPTY BEFORE PROCEEDING
WITH THIS OPERATION.
(1) Recover A/C system refrigerant.
(2) Remove liquid line at filter-drier (Fig. 21).
(3) Remove the (2) bolts holding filter-drier bracket
to radiator fan module bracket.
(4) Remove the lower liquid line at condenser.
(5) Remove the upper radiator crossmember.
(6) Pull up on radiator and slide filter-drier from
the mounting location.
INSTALLATION
(1) Before installation, replace both refrigerant
line O-rings. Then reverse the above procedures.
(2) Evacuate and recharge system.
HEATER A/C UNIT HOUSING
REMOVAL
WARNING: IF EQUIPPED WITH AIR CONDITIONING,
THE REFRIGERATION SYSTEM MUST BE COM-
PLETELY EMPTY BEFORE PROCEEDING.
(1) Set parking brake.
(2) Disconnect battery negative cable.
(3) Using a refrigerant recovery machine, remove
refrigerant from the A/C system.
(4) Remove wiper module. Refer to Group 8K,
Windshield Wipers and Washers.
(5) Drain engine coolant. Remove heater hoses at
the heater core, refer to Heater Hoses Removal and
Installation procedures. Plug coolant lines.(6) Remove suction and liquid lines at the expan-
sion valve (Fig. 27).
(7) Remove the Instrument Panel Assembly. Refer
to Group 8E, Instrument Panel and Systems.
(8) Remove heater ducts.
(9) Disconnect the two upper mounts from the
upper reinforcement and the lower mount from the
tunnel.
(10) Remove the (3) nuts (in the engine compart-
ment) securing the unit to the dash panel (Fig. 30).
(11) Disconnect the HVAC housing wiring harness.
(12) Pull the entire unit rearward until the studs
on the unit clear the dash panel. Drop the unit down.
Pull it rearward to remove it from vehicle.
INSTALLATION
(1) For installation of the assembly, reverse the
above procedures. Install new O-rings on plumbing
inlets
(2) Evacuate and recharge the A/C system.
(3) Perform HVAC control Calibration Diagnostic
and Cooldown test.
HEATER CORE
REMOVAL
(1) Drain coolant system.
(2) Remove left side lower column cover.
(3) Remove steering column assembly. Refer to
Group 19, Steering for service procedure.
(4) Remove ABS module, bracket and wiring (Fig.
31).
(5) Remove I/P to body harness interconnect and
bracket (Fig. 32).
(6) Remove lower silencer boot at base of steering
shaft (Fig. 33)
(7) Pinch off heater lines under the hood.
Fig. 30 HVAC Bolt-Up
24 - 26 HEATING AND AIR CONDITIONINGNS/GS
REMOVAL AND INSTALLATION (Continued)

INSTALLATION
For installation, reverse the above procedures.
Install screws to retain heater core in housing.
Replace heater core tube inlet O-rings. Tighten
heater core tube retaining plate to 361 N´m (276
9 in. lbs.) torque.
HEATER HOSES
REMOVAL
NOTE: Review Safety Precautions and Warnings
before proceeding with this operation.
(1) Drain engine cooling system. Refer to Group 7,
Engine Cooling.
(2) Loosen clamps at each end of heater hose to be
removed (Fig. 38) and (Fig. 39).
CAUTION: When removing hoses from heater core
inlet or outlet nipples, do not use excessive force.
Heater core may become damaged and leak engine
coolant.(3) Carefully rotate hose back and forth while tug-
ging slightly away from connector nipple. If the hose
will not come off, slice the hose at the connector nip-
ple and peel off heater hose. This method will require
heater hose replacement.
INSTALLATION
For installation, reverse the above procedures.
LIQUID LINE
REMOVAL
(1) Disconnect the battery negative cable.
(2) Recover A/C system refrigerant.
(3) Remove ground wire at dash panel.
(4) Remove the nut retaining the refrigerant line
sealing plate to the expansion valve (Fig. 27).
(5) Remove the stud from the expansion valve (Fig.
28).
(6) Remove liquid line from expansion valve.
(7) Cover the openings to prevent contamination.
(8) Disconnect wire connector at pressure trans-
ducer.
(9) Remove liquid line mounting clip at right strut
tower.
(10) Using access slot between radiator crossmem-
ber and grille, loosen liquid line mounting plate at
filter-drier. Remove liquid line from filter-drier.
(11) Remove the old O-rings.
INSTALLATION
For installation, reverse the above procedures.
²Install the stud to the evaporator sealing plate
and tighten 7 to 11 N´m (64 to 96 in. lbs.) torque.
²Install new O-rings.
²Install two-piece line in place of original part.
²Assemble line halves after it is installed on vehi-
cle.
²Evacuate and recharge A/C system.
Fig. 37 Brake Pedal
Fig. 38 Upper Heater Hose
Fig. 39 Lower Heater Hose
24 - 28 HEATING AND AIR CONDITIONINGNS/GS
REMOVAL AND INSTALLATION (Continued)

(7) Remove suction line mounting nut at compres-
sor (Fig. 10).
(8) Remove suction line mounting bracket.
(9) Remove suction line.
INSTALLATION
For installation, reverse the above procedures.
²Install the stud to the evaporator sealing plate
and tighten 7 to 11 N´m (64 to 96 in. lbs.) torque.
²Install new O-rings.
²Install two-piece line in place of original part.
²Assemble line halves after it is installed on vehi-
cle.
²Evacuate and recharge A/C system.
RECIRC DOOR ACTUATOR
REMOVAL
(1) Pull back on carpeting on the right lower floor.
(2) Remove Recirc. door actuator connector.
(3) Remove (3) mounting screws for Recirc. actua-
tor (Fig. 45).(4) Remove Recirc. actuator.
(5) Disengage actuator linkage at Recirc. door.
(6) Remove actuator from vehicle.
INSTALLATION
(1) For installation, reverse the above procedures.
(2) Perform the HVAC control Calibration Diagnos-
tic and Cooldown test.
DISASSEMBLY AND ASSEMBLY
HEATER A/C UNIT RECONDITION
Heater A/C Housing must be removed from vehicle
before performing this operation. Refer to Heater A/C
Unit HousingÐRemoval and Installation.
DISASSEMBLYÐEVAPORATOR HOUSING
(1) Place HVAC unit assembly on workbench.
(2) Remove distribution housing mounting screws
(Fig. 46).
(3) Remove blower motor cover (Fig. 47).
Fig. 44 Right Side Demister Duct
Fig. 45 Recirculation Door Actuator
Fig. 46 Distribution Housing
Fig. 47 Blower Motor Cover
24 - 30 HEATING AND AIR CONDITIONINGNS/GS
REMOVAL AND INSTALLATION (Continued)

cranking. Whenever the Powertrain Control Module
(PCM) sets a Diagnostic Trouble Code (DTC) that
affects vehicle emissions, it illuminates the MIL. If a
problem is detected, the PCM sends a message over
the CCD Bus to the instrument cluster to illuminate
the lamp. The PCM illuminates the MIL only for
DTC's that affect vehicle emissions. The MIL stays
on continuously when the PCM has entered a
Limp-In mode or identified a failed emission compo-
nent or system. The MIL remains on until the DTC
is erased. Refer to the Diagnostic Trouble Code
charts in this group for emission related codes.
Also, the MIL either flashes or illuminates contin-
uously when the PCM detects active engine misfire.
Refer to Misfire Monitoring in this section.
Additionally, the PCM may reset (turn off) the MIL
when one of the following occur:
²PCM does not detect the malfunction for 3 con-
secutive trips (except misfire and fuel system moni-
tors).
²PCM does not detect a malfunction while per-
forming three successive engine misfire or fuel sys-
tem tests. The PCM performs these tests while the
engine is operating within6375 RPM of and within
10 % of the load of the operating condition at which
the malfunction was first detected.
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. From
the state display screen, access either State Display
Inputs and Outputs or State Display Sensors.
STATE DISPLAY INPUTS AND OUTPUTS
Connect the DRB scan tool to the data link connec-
tor and access the State Display screen. Then access
Inputs and Outputs. The following list contains the
PCM system functions accessible through the Inputs
and Outputs screen.
Park/Neutral Switch
Speed Control Resume
Brake Switch
Speed Control On/Off
Speed Control Set
S/C Vent Solenoid
Actual S/C Vent Sol.
S/C Vacuum Solenoid
Actual S/C Vacuum Sol.
S/C Cancel
S/C Last Cutout
S/C Working Status
S/C Denied Status
A/C Clutch Relay
Actual A/C Clutch Relay
EGR Solenoid
Actual EGR Sol.
Automatic Shutdown Relay
Actual Automatic Shutdown Relay
Automatic Shutdown Relay Sense
Radiator Fan Control Module
Actual Radiator Fan Control Module
Duty Cycle EVAP Purge Solenoid
Actual EVAP Purge Sol.
Torque Converter Clutch Solenoid
Power Steering Switch
Closed Loop State
Current CMP Edge
Current CKP State
Current Sync State
Fuel Pump Relay
Actual Fuel Pump Relay
Ignition Sense (A21)
Malfunction Lamp
Limp-in Reason
STATE DISPLAY SENSORS
Connect the DRB scan tool to the vehicle and
access the State Display screen. Then access Sensor
Display. The following list contains the PCM system
functions accessible through the Sensor Display
screen.
Battery Temperature
Engine Coolant Temperature
Engine Coolant Temp Sensor
Throttle Position Volts
Minimum Throttle
Knock Sensor Volts
Battery Voltage
MAP Sensor Reading
Idle Air Control Motor Position
Fig. 1 Data Link (Diagnostic) Connector
25 - 2 EMISSION CONTROL SYSTEMSNS
DESCRIPTION AND OPERATION (Continued)

DIAGNOSTIC TROUBLE CODE DESCRIPTIONS
HEX
CODEGENERIC
SCAN
TOOL
CODEDRB SCAN TOOL
DISPLAYDESCRIPTION OF DIAGNOSTIC
TROUBLE CODE
01 P0340 No Cam Signal at PCM No camshaft signal detected during engine
cranking.
02 P0601 Internal Controller Failure PCM Internal fault condition detected.
05 Charging System Voltage Too Low Battery voltage sense input below target charging
during engine operation. Also, no significant
change detected in battery voltage during active
test of generator output circuit.
06 Charging System Voltage Too High Battery voltage sense input above target charging
voltage during engine operation.
0A* Auto Shutdown Relay Control
CircuitAn open or shorted condition detected in the auto
shutdown relay circuit.
0B Generator Field Not Switching
ProperlyAn open or shorted condition detected in the
generator field control circuit.
0C P0743 Torque Converter Clutch Soleniod/
Trans Relay CircuitsAn open or shorted condition detected in the
torque converter part throttle unlock solenoid
control circuit (3 speed auto RH trans. only).
0E P1491 Rad Fan Control Relay Circuit An open or shorted condition detected in the low
speed radiator fan relay control circuit.
0F* Speed Control Solenoid Circuits An open or shorted condition detected in the
Speed Control vacuum or vent solenoid circuits.
10* A/C Clutch Relay Circuit An open or shorted condition detected in the A/C
clutch relay circuit.
11 P0403 EGR Solenoid Circuit An open or shorted condition detected in the EGR
transducer solenoid circuit.
12 P0443 EVAP Purge Solenoid Circuit An open or shorted condition detected in the duty
cycle purge solenoid circuit.
13 P0203 Injector #3 Control Circuit Injector #3 output driver does not respond properly
to the control signal.
14 P0202 Injector #2 Control Circuit Injector #2 output driver does not respond properly
to the control signal.
15 P0201 Injector #1 Control Circuit Injector #1 output driver does not respond properly
to the control signal.
19 P0505 Idle Air Control Motor Circuits A shorted or open condition detected in one or
more of the idle air control motor circuits.
1A P0122 Throttle Position Sensor Voltage
LowThrottle position sensor input below the minimum
acceptable voltage
1B P0123 Throttle Position Sensor Voltage
HighThrottle position sensor input above the maximum
acceptable voltage.
1E P0117 ECT Sensor Voltage Too Low Engine coolant temperature sensor input below
minimum acceptable voltage.
1F P0118 ECT Sensor Voltage Too High Engine coolant temperature sensor input above
maximum acceptable voltage.
25 - 4 EMISSION CONTROL SYSTEMSNS
DESCRIPTION AND OPERATION (Continued)

HEX
CODEGENERIC
SCAN
TOOL
CODEDRB SCAN TOOL
DISPLAYDESCRIPTION OF DIAGNOSTIC
TROUBLE CODE
92 P1496 5 Volt Supply Output Too Low 5 volt output from regulator does not meet
minimum requirement.
94* P0740 Torq Conv Clu, No RPM Drop At
LockupRelationship between engine speed and vehicle
speed indicates no torque converter clutch
engagement (auto. trans. only).
95* Fuel Level Sending Unit Volts Too
LowOpen circuit between PCM and fuel gauge sending
unit.
96* Fuel Level Sending Unit Volts Too
HighCircuit shorted to voltage between PCM and fuel
gauge sending unit.
97* Fuel Level Unit No Change Over
MilesNo movement of fuel level sender detected.
98 P0703 Brake Switch Stuck Pressed or
ReleasedNo release of brake switch seen after too many
accelerations.
99 P1493 Ambient/Batt Temp Sen VoltsToo
LowBattery temperature sensor input voltage below an
acceptable range.
9A P1492 Ambient/Batt Temp Sensor VoltsToo
HighBattery temperature sensor input voltage above an
acceptable range.
9B P0131 Right Rear (or just) Upstream O2S
Shorted to GroundO2 sensor voltage too low, tested after cold start.
9C P0137 Right Rear (or just) Downstream
O2S Shorted to GroundO2 sensor voltage too low, tested after cold start.
9D P1391 Intermittent Loss of CMP or CKP Intermittent loss of either camshaft or crankshaft
position sensor
A0 P0442 Evap Leak Monitor Small Leak
DetectedA small leak has been detected by the leak
detection monitor.
A1 P0455 Evap Leak Monitor Large Leak
DetectedThe leak detection monitor is unable to pressurize
Evap system, indicating a large leak.
AE P0305 Cylinder #5 Mis-fire Misfire detected in cylinder #5.
AF P0306 Cylinder #6 Mis-fire Misfire detected in cylinder #6.
B7 P1495 Leak Detect ion Pump Solenoid
CircuitLeak detection pump solenoid circuit fault (open or
short).
B8 P1494 Leak Detect Pump Sw or
Mechanical FaultLeak detection pump switch does not respond to
input.
BA P1398 Mis-fire Adaptive Numerator at Limit CKP sensor target windows have too much
variation
BB P1486 Evap Leak Monitor Pinched Hose
FoundPlug or pinch detected between purge solenoid
and fuel tank.
BE P1290 CNG System Pressure Too High Compressed natural gas pressure sensor reading
above acceptable voltage.
C0 P0133 Cat Mon Slow O2 Upstream Oxygen sensor response slower than minimum
required switching frequency during catalyst
monitor.
* Check Engine Lamp (MIL) will not illuminate if this Diagnostic Trouble Code was recorded.
NSEMISSION CONTROL SYSTEMS 25 - 7
DESCRIPTION AND OPERATION (Continued)

conditions are met, the EGR is turned off (solenoid
energized) and the O2S compensation control is mon-
itored. Turning off the EGR shifts the air fuel (A/F)
ratio in the lean direction. The O2S data should indi-
cate an increase in the O2 concentration in the com-
bustion chamber when the exhaust gases are no
longer recirculated. While this test does not directly
measure the operation of the EGR system, it can be
inferred from the shift in the O2S data whether the
EGR system is operating correctly. Because the O2S
is being used, the O2S test must pass its test before
the EGR test.
HEX 6A,6B, 6C, 6D, 6E, AE, and AFÐMISFIRE
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.
HEX 76, 77, 78, and 79ÐFUEL 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 output. The programmed memory
acts as a self calibration tool that the engine control-
ler uses to compensate for variations in engine spec-
ifications, sensor tolerances and engine fatigue over
the life span of the engine. By monitoring the actual
air-fuel ratio with the O2S (short term) and multiply-
ing that with the program long-term (adaptive) mem-
ory and comparing that to the limit, it can be
determined whether it will pass an emissions test. If
a malfunction occurs such that the PCM cannot
maintain the optimum A/F ratio, then the MIL will
be illuminated.
HEX 70, and B4ÐCATALYST 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 O2Ss strategy is based on the fact that as a cat-
alyst deteriorates, its oxygen storage capacity and its
efficiency are both reduced. By monitoring the oxy-
gen storage capacity of a catalyst, its efficiency can
be indirectly calculated. The upstream O2S is used to
detect the amount of oxygen in the exhaust gas
before the gas enters the catalytic converter. The
PCM calculates the A/F mixture from the output of
the O2S. A low voltage indicates high oxygen content
(lean mixture). A high voltage indicates a low content
of oxygen (rich mixture).
When the upstream O2S detects a 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 downstraem O2S will indicate limited activity in
this condition.
As the converter loses the ability to store oxygen,
the condition can be detected from the behavior of
the downstream O2S. When the efficiency drops, no
chemical reaction takes place. This means the con-
centration of oxygen will be the same downstream as
upstream. The output voltage of the downstream
O2S copies the voltage of the upstream sensor. The
only difference is a time lag (seen by the PCM)
between the switching of the O2S's.
To monitor the system, the number of lean-to-rich
switches of upstream and downstream O2S's is
counted. The ratio of downstream switches to
upstream switches is used to determine whether the
catalyst is operating properly. An effective catalyst
will have fewer downstream switches than it has
upstream switches i.e., a ratio closer to zero. For a
totally ineffective catalyst, this ratio will be one-to-
one, indicating that no oxidation occurs in the device.
The system must be monitored so that when cata-
lyst efficiency deteriorates and exhaust emissions
increase to over the legal limit, the MIL (check
engine lamp) will be illuminated.
HEX A0, A1, B7, and B8ÐLEAK DETECTION
PUMP MONITOR
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.
NSEMISSION CONTROL SYSTEMS 25 - 9
DESCRIPTION AND OPERATION (Continued)