2003 CHRYSLER CARAVAN oil pressure

(4) Open both the suction and discharge valves,
then open the charge valve to allow the heated
refrigerant to flow into the system.
(5) When the transfer of refrigerant has stopped,
close both the suction and discharge valves.
(6) If all of the refrigerant charge did not transfer
from the dispensing device, open all of the windows
in the vehicle and set the heater-air conditioner con-
trols so that the compressor is engaged and the
blower motor is operating at its lowest speed setting.
Run the engine at a steady high idle (about 1400
rpm). If the compressor will not engage, test the com-
pressor clutch control circuit and repair as required.
(7) Open the suction valve to allow the remaining
refrigerant to transfer to the refrigerant system.
WARNING: TAKE CARE NOT TO OPEN THE DIS-
CHARGE (HIGH PRESSURE) VALVE AT THIS TIME.
(8) Close the suction valve and test the system
performance. (Refer to 24 - HEATING & AIR CON-
DITIONING - STANDARD PROCEDURE - A/C PER-
FORMANCE TEST).
(9) Disconnect the charging station and manifold
gauge set from the refrigerant system service ports.
(10) Reinstall the caps onto the refrigerant system
service ports.
(11) Run the HVAC Control Cooldown test to ver-
ify proper operation(Refer to 24 - HEATING & AIR
CONDITIONING - DIAGNOSIS AND TESTING).
STANDARD PROCEDURE - REFRIGERANT
SYSTEM EVACUATE
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - A/C PLUMBING)
and (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - CAUTION - A/C PLUMBING).
If the refrigerant system has been open to the
atmosphere, it must be evacuated before the system
can be charged. If moisture and air enters the system
and becomes mixed with the refrigerant, the com-
pressor head pressure will rise above acceptable
operating levels. This will reduce the performance of
the air conditioner and damage the compressor.
Evacuating the refrigerant system will remove the
air and boil the moisture out of the system at near
room temperature. A R-134a refrigerant recovery/re-
cycling/charging station that meets SAE Standard
J2210 must be used to evacuate the refrigerant sys-
tem. See the operating instructions supplied by the
equipment manufacturer for proper care and use ofthis equipment. To evacuate the refrigerant system,
use the following procedure:
NOTE: When connecting the service equipment
couplings to the refrigerant system service ports,
be certain that the valve of each coupling is fully
closed. This will reduce the amount of effort
required to make the connection.
(1) Remove the caps from the refrigerant system
service ports and attach a manifold gauge set and a
R-134a refrigerant recovery/recycling/charging sta-
tion that meets SAE Standard J2210 to the refriger-
ant system.
(2) Open both the suction and discharge valves
and start the charging station vacuum pump.
(3) When the suction gauge has read 88 kPa (26
in. Hg.) vacuum or greater for 45 minutes, close both
the suction and discharge valves and turn off the
vacuum pump. If the refrigerant system fails to
reach the specified vacuum, the system has a leak
that must be corrected. (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - FRONT/RE-
FRIGERANT - STANDARD PROCEDURE -
REFRIGERANT SYSTEM LEAKS).
(4) If the refrigerant system maintains the speci-
fied vacuum for thirty minutes, restart the vacuum
pump, open both the suction and discharge valves,
and evacuate the system for an additional ten min-
utes.
(5) Close both the suction and discharge valves,
and turn off the charging station vacuum pump.
(6) The refrigerant system is now ready to be
charged with R-134a refrigerant. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
FRONT/REFRIGERANT - STANDARD PROCE-
DURE - REFRIGERANT SYSTEM CHARGE).
STANDARD PROCEDURE - REFRIGERANT
RECOVERY
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - A/C PLUMBING)
and (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - CAUTION - A/C PLUMBING).
A R-134a refrigerant recovery/recycling/charging
station that meets SAE Standard J2210 must be
used to recover the refrigerant from an R-134a refrig-
erant system, whenever the refrigerant system must
be opened for service. See the operating instructions
supplied by the equipment manufacturer for the
proper care and use of this equipment.
RSPLUMBING - FRONT24-89
REFRIGERANT (Continued)
ProCarManuals.com

WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - A/C PLUMBING)
and (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - CAUTION - A/C PLUMBING).
(1) Position the suction line into the engine com-
partment.
(2) Remove the tape or plugs from the suction line
and liquid line fittings and both expansion valve
ports.
(3) Lubricate new rubber O-ring seals with clean
refrigerant oil and install them on the suction line
and liquid line fittings.
(4) Reconnect the liquid line and suction line fit-
tings to the expansion valve.
(5) Install and tighten the nut that secures the
suction line and liquid line fittings to the expansion
valve. Tighten the nut to 23 N´m (17 ft. lbs.).
(6) Engage the retainer that secures the suction
line routing clip to the filter-drier mounting bracket
on the side of the right front strut tower in the
engine compartment. (If Equipped).
(7) Remove the tape or plugs from the compressor
suction port and the suction line fitting.
(8) Lubricate a new rubber O-ring seal with clean
refrigerant oil and install it on the suction line fit-
ting.
(9) Install a new dual plan seal and reconnect the
suction line fitting to the compressor suction port.
(10) Install and tighten the nut that secures the
suction line fitting to the compressor. Tighten the nut
to 23 N´m (17 ft. lbs.).
(11) Reconnect the drain tube to the wiper module
drain on the right side of the engine compartment.
(12) Reinstall the air cleaner top cover and snorkel
onto the air cleaner housing located on the right side
of the engine compartment.
(13) Reconnect the battery negative cable.
(14) If the vehicle is equipped with the optional
rear air conditioner, go to Step 15. If the vehicle does
not have the optional rear air conditioner, go to Step
21.
(15) Raise and support the vehicle.
(16) Remove the tape or plugs from the suction
line extension fitting and the underbody suction line
fitting.
(17) Lubricate a new rubber O-ring seal with clean
refrigerant oil and install it on the underbody suction
line fitting.
(18) Reconnect the suction line extension fitting to
the underbody suction line fitting. Tighten the fit-
tings to 23 N´m (17 ft. lbs.).
(19) Install a new tie strap just forward of the con-
nections between the underbody plumbing and theengine compartment plumbing for the rear heater
and air conditioner.
(20) Lower the vehicle.
(21) Evacuate the refrigerant system. (Refer to 24
- HEATING & AIR CONDITIONING/PLUMBING -
FRONT/REFRIGERANT - STANDARD PROCE-
DURE - REFRIGERANT SYSTEM EVACUATE).
(22) Charge the refrigerant system. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
FRONT/REFRIGERANT - STANDARD PROCE-
DURE - REFRIGERANT SYSTEM CHARGE).
SERVICE PORTS
REMOVAL
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - A/C PLUMBING)
and (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - CAUTION - A/C PLUMBING).
(1) Remove the protective cap from the A/C service
port (Fig. 36).
(2) Recover the refrigerant from the refrigerant
system. (Refer to 24 - HEATING & AIR CONDI-
TIONING/PLUMBING - FRONT/REFRIGERANT -
STANDARD PROCEDURE - REFRIGERANT
RECOVERY).
(3) Using a standard Schrader-type valve core tool,
remove the valve core from the A/C service port (Low
Fig. 36 A/C Service Port - Typical
1 - RIGHT FRONT STRUT TOWER
2 - CONNECTOR
3 - A/C PRESSURE TRANSDUCER
4 - RIGHT WIPER MODULE DRAIN TUBE
5 - HIGH SIDE SERVICE PORT
6 - LIQUID LINE
24 - 92 PLUMBING - FRONTRS
SUCTION LINE (Continued)
ProCarManuals.com

PLUMBING - REAR
TABLE OF CONTENTS
page page
EVAPORATOR
DESCRIPTION.........................94
OPERATION...........................94
REMOVAL
REMOVAL - REAR EVAPORATOR.........94
REMOVAL - EVAPORATOR LINE
EXTENSION.........................95
INSTALLATION
INSTALLATION - REAR EVAPORATOR.....96
INSTALLATION - EVAPORATOR LINE
EXTENSION.........................96
EXPANSION VALVE
DESCRIPTION.........................96
OPERATION...........................97
DIAGNOSIS AND TESTING - EXPANSION
VALVE ..............................97
REMOVAL.............................97
INSTALLATION.........................98
HEATER CORE
DESCRIPTION.........................98
OPERATION...........................98STANDARD PROCEDURE - HEATER CORE
FILLING.............................98
REMOVAL.............................99
INSTALLATION........................100
HEATER HOSE
REMOVAL............................100
INSTALLATION........................101
SUCTION LINE
REMOVAL............................101
INSTALLATION........................102
UNDERBODY LINES
DESCRIPTION........................103
OPERATION..........................103
REMOVAL
REMOVAL - REAR HEATER LINES.......104
REMOVAL - REAR AIR CONDITIONING
LINES.............................104
INSTALLATION
INSTALLATION - REAR HEATER LINES....105
INSTALLATION - REAR AIR CONDITIONING
LINES.............................105
EVAPORATOR
DESCRIPTION
The rear evaporator is located in the rear heater-
A/C unit housing, behind the right rear wheel house.
The evaporator is positioned in the rear heater-A/C
housing so that all air that enters the housing must
pass over the fins of the evaporator before it is dis-
tributed through the system ducts and outlets. How-
ever, air passing over the evaporator fins will only be
conditioned when the compressor is engaged and cir-
culating refrigerant through the evaporator tubes.
The rear heater-A/C unit housing must be removed
from the vehicle to access the evaporator for service.
The evaporator cannot be adjusted or repaired and, if
faulty or damaged, it must be replaced.
OPERATION
Refrigerant enters the rear evaporator from the
rear expansion valve as a low-temperature, low-pres-
sure liquid. As air flows over the fins of the evapora-
tor, the humidity in the air condenses on the fins,
and the heat from the air is absorbed by the refrig-
erant. Heat absorption causes the refrigerant to boil
and vaporize. The refrigerant becomes a low-pressure
gas when it leaves the evaporator.
REMOVAL
REMOVAL - REAR EVAPORATOR
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - A/C PLUMBING),
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - CAUTION - A/C PLUMBING),
and (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - HEATER PLUMB-
ING).
(1) Remove the rear heater-A/C unit housing from
the vehicle. (Refer to 24 - HEATING & AIR CONDI-
TIONING/DISTRIBUTION - REAR/REAR HEATER-
A/C HOUSING - REMOVAL).
(2) Remove the rear evaporator line extension from
the expansion valve. (Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING - REAR/EVAPORA-
TOR - REMOVAL - EVAPORATOR LINE EXTEN-
SION).
(3) Remove the rear expansion valve from the rear
evaporator. (Refer to 24 - HEATING & AIR CONDI-
24 - 94 PLUMBING - REARRS
ProCarManuals.com

(6) Remove the nut that secures the expansion
valve bracket to the expansion valve stud.
(7) Remove the expansion valve bracket from the
expansion valve stud.
(8) Remove the nut that secures the evaporator
line extension seal plate to the expansion valve stud.
(9) Remove the evaporator line extension seal
plate from the expansion valve stud.
(10) Remove the evaporator line extension from
the expansion valve and the rear heater-A/C housing
base.
(11) Remove the seals from the evaporator line
extension fittings and discard.
(12) Install plugs in, or tape over the opened evap-
orator line extension fittings and both expansion
valve ports.
INSTALLATION
INSTALLATION - REAR EVAPORATOR
NOTE: If the evaporator is being replaced, add 60
milliliters (2 fluid ounces) of refrigerant oil to the
refrigerant system. Use only refrigerant oil of the
type recommended for the compressor in the vehi-
cle.
(1) Carefully lower the evaporator and its foam
wrap into the lower half of the rear heater-A/C hous-
ing.
(2) Position the upper half of the rear heater-A/C
housing onto the lower half.
(3) Install the three small metal spring clips that
secure the upper half of the rear heater-A/C housing
to the lower half.
(4) Install and tighten the three screws that secure
the upper half of the rear heater-A/C housing to the
lower half. Tighten the screws to 2 N´m (18 in. lbs.).
(5) Install the rubber grommet that seals the evap-
orator inlet and outlet tubes to the rear heater-A/C
housing near the expansion valve.
(6) Reinstall the rear expansion valve onto the
rear evaporator. (Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING - REAR/EXPANSION
VALVE - INSTALLATION).
(7) Reinstall the rear evaporator extension line
onto the expansion valve. (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - REAR/EVAPO-
RATOR - INSTALLATION - EVAPORATOR EXTEN-
SION LINE).
(8) Reinstall the rear heater-A/C unit housing into
the vehicle. (Refer to 24 - HEATING & AIR CONDI-
TIONING/DISTRIBUTION - REAR/REAR HEATER-
A/C HOUSING - INSTALLATION).
INSTALLATION - EVAPORATOR LINE
EXTENSION
(1) Remove the tape or plugs from the evaporator
line extension fittings and both expansion valve
ports.
(2) Lubricate new rubber O-ring seals with clean
refrigerant oil and install them on the evaporator
line extension fittings.
(3) Position the evaporator line extension to the
expansion valve and the rear heater-A/C housing
base.
(4) Position the evaporator line extension seal
plate over the expansion valve stud.
(5) Install and tighten the nut that secures the
evaporator line extension seal plate to the expansion
valve stud. Tighten the nut to 23 N´m (17 ft. lbs.).
(6) Position the expansion valve bracket over the
expansion valve stud.
(7) Install and tighten the two screws that secure
the expansion valve bracket to the lower rear heater-
A/C unit housing. Tighten the screws to 2 N´m (18 in.
lbs.).
(8) Install and tighten the nut that secures the
expansion valve bracket to the expansion valve stud.
Tighten the nut to 23 N´m (17 ft. lbs.).
(9) Carefully restore the expansion valve foam
insulator wrap back around the expansion valve.
(10) Position the plate that captures and seals the
evaporator line extension onto the rear heater-A/C
unit housing base.
(11) Install and tighten the screw that secures the
capture plate to the base of the rear heater-A/C unit
housing. Tighten the screw to 2 N´m (18 in. lbs.).
(12) Reinstall the rear heater-A/C unit housing
into the vehicle. (Refer to 24 - HEATING & AIR
CONDITIONING/DISTRIBUTION - REAR/REAR
HEATER-A/C HOUSING - INSTALLATION).
EXPANSION VALVE
DESCRIPTION
The rear ªHº valve-type thermal expansion valve
(TXV) is located at the rear of the rear heater-A/C
unit housing between the evaporator line extension
and the evaporator coil. High-pressure, low tempera-
ture liquid refrigerant from the liquid line passes
through the expansion valve orifice, converting it into
a low-pressure, low-temperature mixture of liquid
and gas before it enters the evaporator coil. The
expansion valve is a factory calibrated unit and can-
not be adjusted or repaired. If faulty or damaged, the
expansion valve must be replaced.
24 - 96 PLUMBING - REARRS
EVAPORATOR (Continued)
ProCarManuals.com

OPERATION
A mechanical sensor in the expansion valve control
head monitors the temperature and pressure of the
refrigerant leaving the evaporator coil through the
suction line, and adjusts the orifice size at the liquid
line to let the proper amount of refrigerant into the
evaporator coil to meet the vehicle cooling require-
ments. Controlling the refrigerant flow through the
evaporator ensures that none of the refrigerant leav-
ing the evaporator is still in a liquid state, which
could damage the compressor.
DIAGNOSIS AND TESTING - EXPANSION VALVE
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - A/C PLUMBING)
and (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - CAUTION - A/C PLUMBING).
NOTE: The expansion valve should only be tested
following testing of the compressor.
NOTE: Liquid CO
2is required to test the expansion
valve. This material is available from most welding
supply facilities. Liquid CO
2is also available from
companies which service and sell fire extinguish-
ers.
When testing the expansion valve, the work area
and the vehicle temperature must be 21É to 27É C
(70É to 85É F). To test the expansion valve:
(1) Connect a charging station or manifold gauge
set to the refrigerant system service ports. Verify the
refrigerant charge level.
(2) Close all doors, windows and vents to the pas-
senger compartment.
(3) Set the heater-air conditioner controls so that
the compressor is operating, the temperature control
is in the highest temperature position, the mode door
is directing the output to the floor outlets, and the
blower is operating at the highest speed setting.
(4) Start the engine and allow it to idle at 1000
rpm. After the engine has reached normal operating
temperature, allow the passenger compartment to
heat up. This will create the need for maximum
refrigerant flow into the evaporator.
(5) If the refrigerant charge is sufficient, the dis-
charge (high pressure) gauge should read 965 to 1655
kPa (140 to 240 psi). The suction (low pressure)
gauge should read 140 kPa to 207 kPa (20 psi to 30
psi). If OK, go to Step 6. If not OK, replace the faulty
expansion valve.WARNING: PROTECT THE SKIN AND EYES FROM
EXPOSURE TO LIQUID CO
2. PERSONAL INJURY
CAN RESULT.
(6) If the suction (low pressure) gauge reads
within the specified range, freeze the expansion valve
control head for 30 seconds using liquid CO
2or
another suitable super-cold material.Do not spray
R-134a or R-12 refrigerant on the expansion
valve control head for this test.The suction (low
pressure) gauge reading should drop by 10 psi. If OK,
go to Step 7 If not OK, replace the faulty expansion
valve.
(7) Allow the expansion valve control head to thaw.
The suction (low pressure) gauge reading should sta-
bilize at 140 kPa to 240 kPa (20 psi to 30 psi). If not
OK, replace the faulty expansion valve.
(8) When expansion valve testing is complete, test
the overall air conditioner performance. (Refer to 24 -
HEATING & AIR CONDITIONING - DIAGNOSIS
AND TESTING - A/C PERFORMANCE TEST).
Remove all test equipment before returning the vehi-
cle to service.
REMOVAL
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - A/C PLUMBING),
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - CAUTION - A/C PLUMBING),
and (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - HEATER PLUMB-
ING).
(1) Remove the rear heater-A/C unit housing from
the vehicle. (Refer to 24 - HEATING & AIR CONDI-
TIONING/DISTRIBUTION - REAR/REAR HEATER-
A/C HOUSING - REMOVAL).
(2) Carefully remove the foam insulator wrap from
the rear expansion valve.
(3) Remove the rear evaporator line extension from
the expansion valve. (Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING - REAR/EVAPORA-
TOR - REMOVAL - EVAPORATOR LINE EXTEN-
SION).
(4) Remove the two screws that secure the expan-
sion valve to the evaporator tube sealing plate.
(5) Remove the expansion valve from the evapora-
tor tubes.
(6) Remove the seals from the evaporator tube fit-
tings and discard.
(7) Install plugs in, or tape over the opened evap-
orator tube fittings and both expansion valve ports.
RSPLUMBING - REAR24-97
EXPANSION VALVE (Continued)
ProCarManuals.com

(16) Remove the tape or plugs from the suction
line extension fitting and the underbody suction line
fitting (Fig. 35).
(17) Lubricate a new rubber O-ring seal with clean
refrigerant oil and install it on the underbody suction
line fitting.
(18) Reconnect the suction line extension fitting to
the underbody suction line fitting. Tighten the fit-
tings to 23 N´m (17 ft. lbs.).
(19) Install a new tie strap just forward of the con-
nections between the underbody plumbing and the
engine compartment plumbing for the rear heater
and air conditioner.
(20) Lower the vehicle.
(21) Evacuate the refrigerant system. (Refer to 24
- HEATING & AIR CONDITIONING/PLUMBING -
FRONT/REFRIGERANT - STANDARD PROCE-
DURE - REFRIGERANT SYSTEM EVACUATE).
(22) Charge the refrigerant system. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
FRONT/REFRIGERANT - STANDARD PROCE-
DURE - REFRIGERANT SYSTEM CHARGE).UNDERBODY LINES
DESCRIPTION
The rear heater-A/C unit plumbing is used only on
models with the optional rear heater-A/C unit. The
formed metal rear heater-A/C unit suction line, liquid
line, and heater lines are available for separate ser-
vice replacement. The molded and straight heater
hoses used on the rear heater-A/C unit can be ser-
viced in the vehicle. Refer to Group 7 - Cooling Sys-
tem for the heater hose service procedures.
OPERATION
The rear heater and A/C lines are all serviced as
individual pieces. When disconnecting any line or
block ensure that the area around it is clean of any
contaminations that can get in to the system (Fig. 9),
(Fig. 10), (Fig. 12), (Fig. 11) and (Fig. 13).
Any kinks or sharp bends in the rear heater-A/C
unit plumbing will reduce the capacity of the entire
heating and air conditioning system. Kinks and
sharp bends reduce the system flow. High pressures
are produced in the refrigerant system when the air
conditioning compressor is operating. High tempera-
ture coolant is present in the heater plumbing when
the engine is operating. Extreme care must be exer-
cised to make sure that each of the plumbing connec-
tions is pressure-tight and leak free.
Fig. 9 Rear Heater and A/C Lines
1 - HEATER CONNECTION
2 - REAR A/C LINE BLOCK CONNECTION
RSPLUMBING - REAR24 - 103
SUCTION LINE (Continued)
ProCarManuals.com

The following is a list of the monitored compo-
nents:
²Comprehensive Components
²Oxygen Sensor Monitor
²Oxygen Sensor Heater Monitor
²Catalyst Monitor
COMPREHENSIVE COMPONENTS
Along with the major monitors, OBD II requires
that the diagnostic system monitor any component
that could affect emissions levels. In many cases,
these components were being tested under OBD I.
The OBD I requirements focused mainly on testing
emissions-related components for electrical opens and
shorts.
However, OBD II also requires that inputs from
powertrain components to the PCM be tested for
rationality, and that outputs to powertrain compo-
nents from the PCM be tested forfunctionality.
Methods for monitoring the various Comprehensive
Component monitoring include:
(1) Circuit Continuity
²Open
²Shorted high
²Shorted to ground
(2) Rationality or Proper Functioning
²Inputs tested for rationality
²Outputs tested for functionality
NOTE: Comprehensive component monitors are
continuous. Therefore, enabling conditions do not
apply.
Input RationalityÐWhile input signals to the
PCM are constantly being monitored for electrical
opens and shorts, they are also tested for rationality.
This means that the input signal is compared against
other inputs and information to see if it makes sense
under the current conditions.
PCM sensor inputs that are checked for rationality
include:
²Manifold Absolute Pressure (MAP) Sensor
²Oxygen Sensor (O2S)
²Engine Coolant Temperature (ECT) Sensor
²Camshaft Position (CMP) Sensor
²Vehicle Speed Sensor
²Crankshaft Position (CKP) Sensor
²Intake/inlet Air Temperature (IAT) Sensor
²Throttle Position (TPS) Sensor
²Ambient Temperature Sensors
²Power Steering Switch
²Oxygen Sensor Heater
²Brake Switch
²Leak Detection Pump Switch or NVLD switch (if
equipped)
²P/N SwitchOutput FunctionalityÐPCM outputs are tested
for functionality in addition to testing for opens and
shorts. When the PCM provides a voltage to an out-
put component, it can verify that the command was
carried out by monitoring specific input signals for
expected changes. For example, when the PCM com-
mands the Idle Air Control (IAC) Motor to a specific
position under certain operating conditions, it expects
to see a specific (target) idle speed (RPM). If it does
not, it stores a DTC.
PCM outputs monitored for functionality include:
²Fuel Injectors
²Ignition Coils
²Idle Air Control
²Purge Solenoid
²EGR Solenoid (if equipped)
²LDP Solenoid or NVLD solenoid (if equipped)
²Radiator Fan Control
²Trans Controls
OXYGEN SENSOR (O2S) MONITOR
DESCRIPTIONÐEffective 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 operating temperature 300É to 350ÉC
(572É to 662ÉF), the sensor generates a voltage that
is inversely proportional to the amount of oxygen in
the exhaust. When there is a large amount of oxygen
in the exhaust caused by a lean condition, the sensor
produces a low voltage, below 450 mV. When the oxy-
gen content is lower, caused by a rich condition, the
sensor produces a higher voltage, above 450mV (volt-
ages are offset by 2.5 volts on NGC vehicles).
The information obtained by the sensor is used to
calculate the fuel injector pulse width. The PCM is
programmed to maintain the optimum air/fuel ratio.
At this mixture ratio, the catalyst works best to
remove hydrocarbons (HC), carbon monoxide (CO)
and nitrous oxide (NOx) from the exhaust.
The O2S is also the main sensing element for the
EGR (if equipped), Catalyst and Fuel Monitors.
The O2S may fail in any or all of the following
manners:
²Slow response rate (Big Slope)
²Reduced output voltage (Half Cycle)
²Heater Performance
Slow Response Rate (Big Slope)ÐResponse rate
is the time required for the sensor to switch from
lean to rich signal output once it is exposed to a
richer than optimum A/F mixture or vice versa. As
the PCM adjusts the air/fuel ratio, the sensor must
be able to rapidly detect the change. As the sensor
ages, it could take longer to detect the changes in the
oxygen content of the exhaust gas. The rate of
change that an oxygen sensor experiences is called
25 - 2 EMISSIONS CONTROLRS
EMISSIONS CONTROL (Continued)
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ªBig Slopeº. The PCM checks the oxygen sensor volt-
age in increments of a few milliseconds.
Reduced Output Voltage (Half Cycle)ÐThe
output voltage of the O2S ranges from 0 to 1 volt
(voltages are offset by 2.5 volts on NGC vehicles). A
good sensor can easily generate any output voltage in
this range as it is exposed to different concentrations
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. Each
time the voltage signal surpasses the threshold, a
counter is incremented by one. This is called the Half
Cycle Counter.
Heater PerformanceÐThe heater is tested by a
separate monitor. Refer to the Oxygen Sensor Heater
Monitor.
OPERATIONÐAs the Oxygen Sensor signal
switches, the PCM monitors the half cycle and big
slope signals from the oxygen sensor. If during the
test neither counter reaches a predetermined value, a
malfunction is entered and Freeze Frame data is
stored. Only one counter reaching its predetermined
value is needed for the monitor to pass.
The Oxygen Sensor Monitor is a two trip monitor
that is tested only once per trip. When the Oxygen
Sensor fails the test in two consecutive trips, the
MIL is illuminated and a DTC is set. The MIL is
extinguished when the Oxygen Sensor monitor
passes in three consecutive trips. The DTC is erased
from memory after 40 consecutive warm-up cycles
without test failure.
Enabling ConditionsÐThe following conditions
must typically be met for the PCM to run the oxygen
sensor monitor:
²Battery voltage
²Engine temperature
²Engine run time
²Engine run time at a predetermined speed
²Engine run time at a predetermined speed and
throttle opening
²Transmission in gear and brake depressed (auto-
matic only)
²Fuel system in Closed Loop
²Long Term Adaptive (within parameters)
²Power Steering Switch in low PSI (no load)
²Engine at idle
²Fuel level above 15%
²Ambient air temperature
²Barometric pressure
²Engine RPM within acceptable range of desired
idle
Pending ConditionsÐThe Task Manager typi-
cally does not run the Oxygen Sensor Monitor if over-
lapping monitors are running or the MIL is
illuminated for any of the following:²Misfire Monitor
²Front Oxygen Sensor and Heater Monitor
²MAP Sensor
²Vehicle Speed Sensor
²Engine Coolant Temperature Sensor
²Throttle Position Sensor
²Engine Controller Self Test Faults
²Cam or Crank Sensor
²Injector and Coil
²Idle Air Control Motor
²EVAP Electrical
²EGR Solenoid Electrical (if equipped)
²Intake/inlet Air Temperature
²5 Volt Feed
ConflictÐThe Task Manager does not run the
Oxygen Sensor Monitor if any of the following condi-
tions are present:
²A/C ON (A/C clutch cycling temporarily sus-
pends monitor)
²Purge flow in progress
²Ethanol content learn is taking place and the
ethanol used once flag is set (if equipped)
SuspendÐThe Task Manager suspends maturing
a fault for the Oxygen Sensor Monitor if any of the
following are present:
²Oxygen Sensor Heater Monitor, Priority 1
²Misfire Monitor, Priority 2
OXYGEN SENSOR HEATER MONITOR
DESCRIPTIONÐIf there is an oxygen sensor
(O2S) DTC as well as a O2S heater DTC, the O2S
fault MUST be repaired first. After the O2S fault is
repaired, verify that the heater circuit is operating
correctly.
The voltage readings taken from the O2S are very
temperature sensitive. The readings are not accurate
below a sensor temperature of 300ÉC. Heating of the
O2S 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 must be tested to
ensure that it is heating the sensor properly.
The heater element itself is not tested. The sensor
output is used to test the heater by isolating the
effect of the heater element on the O2S output volt-
age from the other effects. The resistance is normally
between 100 ohms and 4.5 megaohms. When oxygen
sensor temperature increases, the resistance in the
internal circuit decreases. The PCM sends a 5 volts
biased signal through the oxygen sensors to ground
this monitoring circuit. As the temperature increases,
resistance decreases and the PCM detects a lower
voltage at the reference signal. Inversely, as the tem-
perature decreases, the resistance increases and the
PCM detects a higher voltage at the reference signal.
The O2S circuit is monitored for a drop in voltage.
RSEMISSIONS CONTROL25-3
EMISSIONS CONTROL (Continued)
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