2002 CHRYSLER CARAVAN oil pressure

²Single or Dual Zone (Front Unit Only - with
2.5L Turbo Diesel)0.91 kilograms (2.00 pounds or
32 ounces)
²Single or Dual Zone (Front Unit Only)- 0.96
kilograms (2.13 pounds or 34 ounces)
²Three Zone (Front and Rear Units)- 1.31
kilograms (2.88 pounds or 46 ounces)
CHARGING PROCEDURE
(1) Evacuate the refrigerant system. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
FRONT/REFRIGERANT - STANDARD PROCE-
DURE - REFRIGERANT SYSTEM EVACUATE).
(2) A manifold gauge set and a R-134a refrigerant
recovery/recycling/charging station that meets SAE
Standard J2210 should still be connected to the
refrigerant system.
(3) Measure the proper amount of refrigerant and
heat it to 52É C (125É F) with the charging station.
See the operating instructions supplied by the equip-
ment manufacturer for proper use of this equipment.
(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 BEFOREPERFORMING 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 of
this 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).
24 - 92 PLUMBING - FRONTRS
REFRIGERANT (Continued)
ProCarManuals.com

INSTALLATION
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) 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 com-
pressor in the vehicle.
(2) Remove the tape or plug from the A/C service
port.
(3) Using a standard Schrader-type valve core tool,
install and tighten the replacement valve core into
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.
(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) Reinstall the protective cap onto the A/C ser-
vice port.
Fig. 39 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 - 96 PLUMBING - FRONTRS
SERVICE PORTS (Continued)
ProCarManuals.com

PLUMBING - REAR
TABLE OF CONTENTS
page page
EVAPORATOR
DESCRIPTION.........................97
OPERATION...........................97
REMOVAL
REMOVAL - REAR EVAPORATOR.........97
REMOVAL - EVAPORATOR LINE
EXTENSION.........................98
INSTALLATION
INSTALLATION - REAR EVAPORATOR.....99
INSTALLATION - EVAPORATOR LINE
EXTENSION.........................99
EXPANSION VALVE
DESCRIPTION.........................99
OPERATION..........................100
DIAGNOSIS AND TESTING - EXPANSION
VALVE .............................100
REMOVAL............................100
INSTALLATION........................101
HEATER CORE
DESCRIPTION........................101
OPERATION..........................101STANDARD PROCEDURE - HEATER CORE
FILLING............................101
REMOVAL............................102
INSTALLATION........................103
HEATER HOSE
REMOVAL............................103
INSTALLATION........................103
SUCTION LINE
REMOVAL............................104
INSTALLATION........................105
UNDERBODY LINES
DESCRIPTION........................106
OPERATION..........................106
REMOVAL
REMOVAL - REAR HEATER LINES.......107
REMOVAL - REAR AIR CONDITIONING
LINES.............................107
INSTALLATION
INSTALLATION - REAR HEATER LINES....108
INSTALLATION - REAR AIR CONDITIONING
LINES.............................108
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-
RSPLUMBING - REAR24-97
ProCarManuals.com

(5) Remove the two screws that secure the expan-
sion valve bracket to the lower rear heater-A/C unit
housing.
(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.
RSPLUMBING - REAR24-99
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 is required to test the expansion
valve. This material is available from most welding
supply facilities. Liquid CO is 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. 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 or
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.
24 - 100 PLUMBING - REARRS
EXPANSION VALVE (Continued)
ProCarManuals.com

INSTALLATION
NOTE: If the rear heater core or the rear heater-A/C
housing have been removed from the vehicle for
service, the rear heater core may be pre-filled with
the proper engine coolant mixture prior to recon-
necting the heater hoses to the heater core hose fit-
tings. (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - REAR/HEATER CORE - STANDARD
PROCEDURE - HEATER CORE FILLING).
(1) Carefully slide the heater core into the rear
heater-A/C unit housing.
(2) Using hand pressure, press firmly and evenly
on the heater core end plate until the four latch tabs
that secure the heater core in the rear heater-A/C
unit housing are fully engaged (Fig. 5).
(3) Remove the plugs or tape from the heater core
fittings and both heater hoses.
(4) Reconnect the heater hoses to the rear heater
core. (Refer to 24 - HEATING & AIR CONDITION-
ING/PLUMBING - REAR/HEATER HOSE - INSTAL-
LATION).
(5) Install and tighten the screw that secures the
front of the rear heater-A/C unit housing to the right
quarter inner panel. Tighten the screw to 11 N´m (97
in. lbs.).
(6) Install and tighten the screw that secures the
back of the rear heater-A/C unit housing to the right
D-pillar. Tighten the screw to 11 N´m (97 in. lbs.).
(7) Reinstall the rear heater distribution duct onto
the right quarter inner panel. (Refer to 24 - HEAT-ING & AIR CONDITIONING/DISTRIBUTION -
REAR/REAR HEATER DISTRIBUTION DUCT -
INSTALLATION).
(8) Remove the right quarter trim panel and right
D-pillar trim panel from the quarter inner panel.
(Refer to 23 - BODY/INTERIOR/QUARTER TRIM
PANEL - INSTALLATION).
(9) Drain the engine cooling system. (Refer to 7 -
COOLING - STANDARD PROCEDURE - COOLING
SYSTEM REFILL).
HEATER HOSE
REMOVAL
REFER TO THE APPLICABLE WARNINGS AND
CAUTIONS FOR THIS SYSTEM BEFORE PER-
FORMING THE FOLLOWING OPERATION. (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMB-
ING FRONT - WARNING - HEATER PLUMBING).
(1) Partially drain engine cooling system. Refer to
Group 7, Engine Cooling.
(2) Loosen clamp at the front end of the hose
located at the right, outboard side of the underbody,
rearward of the front crossmember. (Fig. 9)
(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.
CAUTION:
When removing hoses from outlet nipples, do not
use excessive force. Outlet nipples may become
damaged and leak engine coolant.
(4) Compress insert in rear heater hose quick con-
nection and pull downward on hose. (Fig. 11)
(5) Remove (3) straps securing underbody lines.
(Fig. 8)
(6) Separate and remove rear heater lines from
vehicle.
INSTALLATION
There are several heater core plumbing configura-
tions used on this model, depending upon the engine
size and other optional equipment. One plumbing
configuration is used for all 2.4L engines, while the
3.3L and 3.8L engines have unique heater return
plumbing on the engine for models with or without
an optional engine oil cooler. There are also unique
plumbing configurations at the heater core for mod-
els with or without the optional rear heater and air
conditioner. All models use a combination of formed
steel tubing and rubber hoses. In most cases, the
rubber hose is secured to the steel tubing with a
spring tension clamp.
Fig. 5 Heater Core
1 - REAR HEATER-A/C HOUSING OUTLET
2 - REAR HEATER-A/C UNIT HOUSING
3 - LATCH (4)
4 - HEATER CORE
5 - RIGHT REAR WHEEL HOUSE
6 - HEATER HOSES
RSPLUMBING - REAR24 - 103
HEATER CORE (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/Battery Temperature Sensors
²Power Steering Switch
²Oxygen Sensor Heater
²Engine Controller
²Brake Switch
²Leak Detection Pump Switch (if equipped)
²P/N Switch
²Trans ControlsOutput 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
²Torque Converter Clutch Solenoid
²Idle Air Control
²Purge Solenoid
²EGR Solenoid (if equipped)
²LDP 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.
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)
ProCarManuals.com

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. 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 Monitor²Front 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
²Ethanel content learn is takeng place and the
ethenal 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 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.
OPERATIONÐThe Oxygen Sensor Heater Moni-
tor begins after the ignition has been turned OFF.
RSEMISSIONS CONTROL25-3
EMISSIONS CONTROL (Continued)
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