fuel DODGE RAM 2003 Service Repair Manual

TIRE CHAINS
Tire snow chains may be used oncertainmodels.
Refer to the Owner's Manual for more information.
DESCRIPTION - RADIAL ± PLY TIRES
Radial-ply tires improve handling, tread life and
ride quality, and decrease rolling resistance.
Radial-ply tires must always be used in sets of
four. Under no circumstances should they be used on
the front only. They may be mixed with temporary
spare tires when necessary. A maximum speed of 50
MPH is recommended while a temporary spare is in
use.
Radial-ply tires have the same load-carrying capac-
ity as other types of tires of the same size. They also
use the same recommended inflation pressures.
The use of oversized tires, either in the front or
rear of the vehicle, can cause vehicle drive train fail-
ure. This could also cause inaccurate wheel speed
signals when the vehicle is equipped with Anti-Lock
Brakes.
The use of tires from different manufactures on the
same vehicle is NOT recommended. The proper tire
pressure should be maintained on all four tires.
DESCRIPTION - TIRE PRESSURE FOR HIGH
SPEEDS
Where speed limits allow the vehicle to be driven at
high speeds, correct tire inflation pressure is very
important. For speeds up to and including 120 km/h (75
mph), tires must be inflated to the pressures shown on
the tire placard. For continuous speeds in excess of 120
km/h (75 mph), tires must be inflated to the maximum
pressure specified on the tire sidewall.
Vehicles loaded to the maximum capacity should not
be driven at continuous speeds above 75 mph (120
km/h).
For emergency vehicles that are driven at speeds
over 90 mph (144 km/h), special high speed tires
must be used. Consult tire manufacturer for correct
inflation pressure recommendations.
DESCRIPTION - REPLACEMENT TIRES
The original equipment tires provide a proper bal-
ance of many characteristics such as:
²Ride
²Noise
²Handling
²Durability
²Tread life
²Traction
²Rolling resistance
²Speed capability
It is recommended that tires equivalent to the orig-
inal equipment tires be used when replacement is
needed.
Failure to use equivalent replacement tires may
adversely affect the safety and handling of the vehicle.
The use of oversize tires may cause interference
with vehicle components. Under extremes of suspen-
sion and steering travel, interference with vehicle
components may cause tire damage.
WARNING: FAILURE TO EQUIP THE VEHICLE WITH
TIRES HAVING ADEQUATE SPEED CAPABILITY
CAN RESULT IN SUDDEN TIRE FAILURE.
DESCRIPTION - TIRE INFLATION PRESSURES
Under inflation will cause rapid shoulder wear, tire
flexing, and possible tire failure (Fig. 12).
Over inflation will cause rapid center wear and
loss of the tire's ability to cushion shocks (Fig. 13).
Improper inflation can cause:
²Uneven wear patterns
²Reduced tread life
²Reduced fuel economy
²Unsatisfactory ride
²Vehicle drift
For proper tire pressure specification refer to the Tire
Inflation Pressure Chart provided with the vehicles
Fig. 11 Tire Identification
22 - 6 TIRES/WHEELSDR
TIRES (Continued)

SPECIFICATIONS - TORQUE
TORQUE SPECIFICATIONS
Description N´m Ft. Lbs. In. Lbs.
A-pillar trim/grab handle bolts 6 Ð 55
Body Isolator/cab bolts 81 60 Ð
Cargo box bolts 108 80 Ð
Cargo box tie down/cleat bolts 34 25 Ð
Center seat assembly nuts*25 18 Ð
Center seat cushion/hinge bolts*20 15 Ð
Center seat back hinge to storage bin bolts*25 18 Ð
Center seat back free pivot hinge bolt*25 18 Ð
Center seat back inertia hinge pivot bolt*10 Ð 89
Center seat inertia hinge to seat back bolts*25 18 Ð
Fender bolts - front lower 9 Ð 80
Fender bolts - lower inside 17 13 Ð
Fender to hinge support bolts 11 8 Ð
Fender to upper fender rail bolts 9 Ð 80
Footmans loop bolts 12 9 Ð
Front center seat nuts*25 18 Ð
Front door glass lift plate nuts 10 Ð 89
Front door hinge to a-pillar nuts 28 21 Ð
Front door hinge to door nuts/bolts 28 21 Ð
Front door inside handle bolt 9 Ð 80
Front door latch adjustment screw 3 Ð 30
Front door latch assembly bolts 10 Ð 89
Front door latch striker bolts 28 21 Ð
Front door latch striker bolts 28 21 Ð
Front door regulator bolts 10 Ð 89
Front door regulator stabilizer nuts 10 Ð 89
Front door remote handle actuator nuts 10 Ð 89
Front door run channel screws 10 Ð 89
Front seat assembly front bolts*28 30 Ð
Front seat assembly rear bolts*40 30 Ð
Front seat track nuts*25 18 Ð
Fuel fill door bolts 9 Ð 80
Hood hinge to fender rail bolts 20 15 Ð
Hood latch bolts 11 8 Ð
Hood latch striker/safety catch bolts 11 8 Ð
Hood hinge to hood nuts 23 17 Ð
Instrument panel center bracket bolts 12 9 Ð
Instrument panel column support bolts 14 10 Ð
Instrument panel side mounting bolts 12 9 Ð
23 - 12 BODYDR
BODY (Continued)

EXTERIOR
TABLE OF CONTENTS
page page
BODY SIDE MOLDINGS
REMOVAL.............................36
INSTALLATION.........................36
BODY ISOLATORS
REMOVAL.............................36
INSTALLATION.........................37
CARGO BOX
REMOVAL.............................37
INSTALLATION.........................37
CARGO BOX - TIE DOWN
REMOVAL.............................37
INSTALLATION.........................37
COWL GRILLE
REMOVAL.............................38
INSTALLATION.........................38
EXTERIOR NAME PLATES
REMOVAL.............................38
INSTALLATION.........................38
FRONT FENDER
REMOVAL.............................39
INSTALLATION.........................39
FUEL FILL DOOR
REMOVAL.............................39
INSTALLATION.........................39GRILLE
REMOVAL.............................39
INSTALLATION.........................40
GRILLE FRAME
REMOVAL.............................40
INSTALLATION.........................40
FRONT WHEELHOUSE SPLASH SHIELD
REMOVAL.............................40
INSTALLATION.........................41
REAR WHEELHOUSE SPLASH SHIELD
REMOVAL.............................41
INSTALLATION.........................41
SIDE VIEW MIRROR
REMOVAL.............................41
INSTALLATION.........................41
UPPER RADIATOR CROSSMEMBER
REMOVAL.............................42
INSTALLATION.........................42
SIDE VIEW MIRROR GLASS
REMOVAL.............................42
INSTALLATION.........................44
REAR FENDER
REMOVAL.............................44
INSTALLATION.........................44
BODY SIDE MOLDINGS
REMOVAL
NOTE: Body side moldings are attached to the body
panels with adhesive tape.
(1) Apply a length of masking tape on the body
panel, parallel to the top edge of the molding and to
one end to use as a guide for installation, if neces-
sary.
(2) If temperature is below 21ÉC (70ÉF) warm
molding with a heat lamp or gun. Do not exceed 52ÉC
(120ÉF) when heating molding.
(3) Using a trim stick C-4755 or equivalent,
remove and discard the molding from the outside of
the body panel.
INSTALLATION
(1) Thoroughly clean all residue from the body side
molding attachment area of the body panel.(2) Wipe area with a clean lint free cloth moist-
ened with a 50% solution of water and alcohol and
wipe dry immediately with a dry lint free cloth.
(3) Apply new body side molding using the guide
tape on the body panel and apply consistent and uni-
form pressure of approximately 40 p.s.i. over the
entire surface of the molding.
BODY ISOLATORS
REMOVAL
(1) Loosen all cab to frame mounting bolts (six
standard cab, eight quad cab). (Fig. 1)
(2) Remove the mounting bolts and rebound cush-
ions
(3) Using a floor jack and block of wood under the
cab sill, lift the body to gain access to the isolators.
(4) Remove the isolators.
(5) Install new isolators and repeat steps one
through 4, for the opposite side.
23 - 36 EXTERIORDR

INSTALLATION
(1) For the rear isolators install the rebound cush-
ions, washers, reinforcement plates and bolts. (Fig. 1)
(2) Install the remaining rebound cushions and
bolts.
(3) Tighten the bolts to 81 N´m (60 ft. lbs.).
CARGO BOX
REMOVAL
(1) Disconnect the fuel fill hose and vent hose.
(Refer to 14 - FUEL SYSTEM/FUEL DELIVERY/
FUEL TANK - REMOVAL)
(2) Disconnect the tail lamp wire harness.
(3) Remove the cargo box bolts. (Fig. 2) or (Fig. 3)
(4) Remove the cargo box.
INSTALLATION
(1) Install the cargo box and install the bolts.
(2) Tighten the bolts to 108 N´m (80 ft. lbs.).
(3) Connect the fuel fill and vent hoses. (Refer to
14 - FUEL SYSTEM/FUEL DELIVERY/FUEL TANK
- INSTALLATION)
(4) Connect the tail lamp wire harness.CARGO BOX - TIE DOWN
REMOVAL
(1) Remove the bolts and remove the tie down
cleat. (Fig. 4)
INSTALLATION
(1) Install the tie down cleat and install the bolts.
(2) Tighten the bolts to 34 N´m (25 ft. lbs.).
Fig. 1 BODY ISOLATORS - TYPICAL
1 - CAB SILL
2 - ISOLATORS
3 - REBOUND CUSHION
4 - WASHER (REAR ISOLATOR ONLY)
5 - BOLTS
6 - REINFORCEMENT PLATE (REAR ISOLATOR ONLY)
Fig. 2 SHORT CARGO BOX
1 - CARGO BOX
2 - FRAME
3 - BOLTS (3 PER SIDE)
Fig. 3 LONG CARGO BOX
1 - CARGO BOX
2 - FRAME
3 - BOLTS (4 PER SIDE)
DREXTERIOR 23 - 37
BODY ISOLATORS (Continued)

FRONT FENDER
REMOVAL
(1) Remove the antenna, if equipped. (Refer to 8 -
ELECTRICAL/AUDIO/ANTENNA BODY & CABLE -
REMOVAL)
(2) Remove the battery tray, if required. (Refer to 8
- ELECTRICAL/BATTERY SYSTEM/TRAY -
REMOVAL)
(3) Remove the cowl grille. (Refer to 23 - BODY/
EXTERIOR/COWL GRILLE - REMOVAL)
(4) Remove the headlamp unit. (Refer to 8 - ELEC-
TRICAL/LAMPS/LIGHTING - EXTERIOR/HEAD-
LAMP UNIT - REMOVAL)
(5) Remove the wheelhouse splash shield. (Refer to
23 - BODY/EXTERIOR/FRONT WHEELHOUSE
SPLASH SHIELD - REMOVAL)
(6) Remove the inside and lower bolts. (Fig. 6)
(7) Remove the two bolts below the headlamp.
(8) Remove the hinge support bolt at the cowl.
(9) Remove the three bolts along the fender rail.
INSTALLATION
(1) Install the three bolts along the upper fender
rail and tighten to 9 N´m (80 in. lbs.).
(2) Install the upper hinge support bolt at the cowl
and tighten to 17 N´m (13 ft. lbs.).
(3) Install the two bolts below the headlamp and
tighten to 9 N´m (80 in. lbs.).
(4) Install the inside and lower bolts and tighten
to 17 N´m (13 ft. lbs.).
(5) Check the fender positioning and adjust as
required by adding shims. (Refer to 23 - BODY/BODY STRUCTURE/GAP AND FLUSH - SPECIFI-
CATIONS)
(6) Install the wheelhouse splash shield. (Refer to
23 - BODY/EXTERIOR/FRONT WHEELHOUSE
SPLASH SHIELD - INSTALLATION)
(7) Install the headlamp unit. (Refer to 8 - ELEC-
TRICAL/LAMPS/LIGHTING - EXTERIOR/HEAD-
LAMP UNIT - INSTALLATION)
(8) Install the cowl grille. (Refer to 23 - BODY/EX-
TERIOR/COWL GRILLE - INSTALLATION)
(9) Install the battery tray, if required. (Refer to 8
- ELECTRICAL/BATTERY SYSTEM/TRAY -
INSTALLATION)
(10) Install the antenna, if required. (Refer to 8 -
ELECTRICAL/AUDIO/ANTENNA BODY & CABLE -
INSTALLATION)
FUEL FILL DOOR
REMOVAL
(1) Open fill door and remove the bolts. (Fig. 7)
(2) Remove the door.
INSTALLATION
(1) Install the fuel fill door.
(2) Install the bolts and tighten to 9 N´m (80 in.
lbs.).
GRILLE
REMOVAL
(1) Open the hood.
(2) Remove the six lower screws. (Fig. 8)
(3) Remove the six upper nuts and separate the
grille from the grille frame.
Fig. 6 FRONT FENDER
1 - HOOD HINGE SUPPORT BOLT (1)
2 - HOOD HINGE
3 - INNER BOLT (1)
4 - FRONT BOLTS (2)
5 - LOWER BOLT INSERT
6 - FENDER
7 - UPPER BOLTS (3)Fig. 7 FUEL FILL DOOR
1 - FUEL FILL DOOR
2 - BOLTS (2)
DREXTERIOR 23 - 39

NOTE:
All measurements are in mm.
O/F = Over Flush
U/F = Under Flush
DIMENSION DESCRIPTION GAP FLUSH
1 Tailgate to outer box
(Up/Down surface only)Ð 0.0   1.5
Parallel within 1.0
2 Cab Back to box front 31.0   5.0
Parallel within 3.0Ð
3 Fuel door to outer box 5.0   1.5
Parallel within 1.00.0   1.5
4 Cab to box side 31.0   5.0
Parallel within 3.04.0   2.5 (Standard Cab)
O/F 5.0   2.5 (Quad Cab)
5 Cab to box character line alignment Ð Up/Down 0.0   3.0
6 Tailgate to outer box 5.0   2.0
Parallel within 1.0U/F 1.5   1.5
7 Bumper to outer box 24.75   5.0 (F/A)
23.75   5.0 (C/C)
Parallel within 5.0Ð
8 Tailgate to outer box character line
adjustmentÐ Up/Down 0.0   1.5
9 Bumper to tailgate 30.25   3.0
Parallel within 4.0Ð
Fig. 3 GAP & FLUSH - PICKUP BOX
23 - 98 BODY STRUCTUREDR
GAP AND FLUSH (Continued)

EMISSIONS CONTROL
TABLE OF CONTENTS
page page
EMISSIONS CONTROL
DESCRIPTION
DESCRIPTION - STATE DISPLAY TEST
MODE...............................1
DESCRIPTION - CIRCUIT ACTUATION TEST
MODE...............................1
DESCRIPTION - DIAGNOSTIC TROUBLE
CODES..............................1
DESCRIPTION - TASK MANAGER..........1DESCRIPTION - MONITORED SYSTEMS....1
DESCRIPTION - TRIP DEFINITION.........4
DESCRIPTION - COMPONENT MONITORS . . 4
OPERATION
OPERATION..........................4
OPERATION - TASK MANAGER...........5
OPERATION - NON-MONITORED CIRCUITS . . 8
EVAPORATIVE EMISSIONS................10
EMISSIONS CONTROL
DESCRIPTION
DESCRIPTION - STATE DISPLAY TEST MODE
The switch inputs to the Powertrain Control Mod-
ule (PCM) have two recognized states; HIGH and
LOW. For this reason, the PCM cannot recognize the
difference between a selected switch position versus
an open circuit, a short circuit, or a defective switch.
If the State Display screen shows the change from
HIGH to LOW or LOW to HIGH, assume the entire
switch circuit to the PCM functions properly. Connect
the DRB scan tool to the data link connector and
access the state display screen. Then access either
State Display Inputs and Outputs or State Display
Sensors.
DESCRIPTION - CIRCUIT ACTUATION TEST
MODE
The Circuit Actuation Test Mode checks for proper
operation of output circuits or devices the Powertrain
Control Module (PCM) may not internally recognize.
The PCM attempts to activate these outputs and
allow an observer to verify proper operation. Most of
the tests provide an audible or visual indication of
device operation (click of relay contacts, fuel spray,
etc.). Except for intermittent conditions, if a device
functions properly during testing, assume the device,
its associated wiring, and driver circuit work cor-
rectly. Connect the DRB scan tool to the data link
connector and access the Actuators screen.
DESCRIPTION - DIAGNOSTIC TROUBLE CODES
A Diagnostic Trouble Code (DTC) indicates the
PCM has recognized an abnormal condition in the
system.Remember that DTC's are the results of a sys-
tem or circuit failure, but do not directly iden-
tify the failed component or components.
BULB CHECK
Each time the ignition key is turned to the ON
position, the malfunction indicator (check engine)
lamp on the instrument panel should illuminate for
approximately 2 seconds then go out. This is done for
a bulb check.
OBTAINING DTC'S USING DRB SCAN TOOL
(1) Obtain the applicable Powertrain Diagnostic
Manual.
(2) Obtain the DRB Scan Tool.
(3) Connect the DRB Scan Tool to the data link
(diagnostic) connector. This connector is located in
the passenger compartment; at the lower edge of
instrument panel; near the steering column.
(4) Turn the ignition switch on and access the
ªRead Faultº screen.
(5) Record all the DTC's and ªfreeze frameº infor-
mation shown on the DRB scan tool.
(6) To erase DTC's, use the ªErase Trouble Codeº
data screen on the DRB scan tool.Do not erase any
DTC's until problems have been investigated
and repairs have been performed.
DESCRIPTION - TASK MANAGER
The PCM is responsible for efficiently coordinating
the operation of all the emissions-related compo-
nents. The PCM is also responsible for determining if
the diagnostic systems are operating properly. The
software designed to carry out these responsibilities
is call the 'Task Manager'.
DESCRIPTION - MONITORED SYSTEMS
There are new electronic circuit monitors that
check fuel, emission, engine and ignition perfor-
DREMISSIONS CONTROL 25 - 1

mance. These monitors use information from various
sensor circuits to indicate the overall operation of the
fuel, engine, ignition and emission systems and thus
the emissions performance of the vehicle.
The fuel, engine, ignition and emission systems
monitors do not indicate a specific component prob-
lem. They do indicate that there is an implied prob-
lem within one of the systems and that a specific
problem must be diagnosed.
If any of these monitors detect a problem affecting
vehicle emissions, the Malfunction Indicator Lamp
(MIL) will be illuminated. These monitors generate
Diagnostic Trouble Codes that can be displayed with
the MIL or a scan tool.
The following is a list of the system monitors:
²Misfire Monitor
²Fuel System Monitor
²Oxygen Sensor Monitor
²Oxygen Sensor Heater Monitor
²Catalyst Monitor
²Leak Detection Pump Monitor (if equipped)
All these system monitors require two consecutive
trips with the malfunction present to set a fault.
Refer to the appropriate Powertrain Diagnos-
tics Procedures manual for diagnostic proce-
dures.
The following is an operation and description of
each system monitor :
OXYGEN SENSOR (O2S) MONITOR
Effective 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 oper-
ating temperature 300É to 350ÉC (572É to 662ÉF), the
sensor generates a voltage that is inversely propor-
tional to the amount of oxygen in the exhaust. The
information obtained by the sensor is used to calcu-
late the fuel injector pulse width. This maintains a
14.7 to 1 Air Fuel (A/F) ratio. At this mixture ratio,
the catalyst works best to remove hydrocarbons (HC),
carbon monoxide (CO) and nitrogen oxide (NOx) from
the exhaust.
The O2S is also the main sensing element for the
Catalyst and Fuel Monitors.
The O2S can fail in any or all of the following
manners:
²slow response rate
²reduced output voltage
²dynamic shift
²shorted or open circuits
Response rate is the time required for the sensor to
switch from lean to rich once it is exposed to a richer
than optimum A/F mixture or vice versa. As the sen-
sor starts malfunctioning, it could take longer todetect the changes in the oxygen content of the
exhaust gas.
The 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 con-
centrations 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.
OXYGEN SENSOR HEATER MONITOR
If there is an oxygen sensor (O2S) shorted to volt-
age DTC, as well as a O2S heater DTC, the O2S
fault MUST be repaired first. Before checking the
O2S fault, verify that the heater circuit is operating
correctly.
Effective 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 oper-
ating temperature 300É to 350ÉC (572 É to 662ÉF), the
sensor generates a voltage that is inversely propor-
tional to the amount of oxygen in the exhaust. The
information obtained by the sensor is used to calcu-
late the fuel injector pulse width. This maintains a
14.7 to 1 Air Fuel (A/F) ratio. At this mixture ratio,
the catalyst works best to remove hydrocarbons (HC),
carbon monoxide (CO) and nitrogen oxide (NOx) from
the exhaust.
The voltage readings taken from the O2S sensor
are very temperature sensitive. The readings are not
accurate below 300ÉC. Heating of the O2S sensor 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 sensor must be tested to ensure
that it is heating the sensor properly.
The O2S sensor circuit is monitored for a drop in
voltage. The sensor output is used to test the heater
by isolating the effect of the heater element on the
O2S sensor output voltage from the other effects.
LEAK DETECTION PUMP MONITOR (IF EQUIPPED)
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.
The primary components within the assembly are:
A three port solenoid that activates both of the func-
tions listed above; a pump which contains a switch,
two check valves and a spring/diaphragm, a canister
vent valve (CVV) seal which contains a spring loaded
vent seal valve.
Immediately after a cold start, between predeter-
mined temperature thresholds limits, the three port
solenoid is briefly energized. This initializes the
25 - 2 EMISSIONS CONTROLDR
EMISSIONS CONTROL (Continued)

pump by drawing air into the pump cavity and also
closes the vent seal. During non test conditions the
vent seal is held open by the pump diaphragm
assembly which pushes it open at the full travel posi-
tion. The vent seal will remain closed while the
pump is cycling due to the reed switch triggering of
the three port solenoid that prevents the diaphragm
assembly from reaching full travel. After the brief
initialization period, the solenoid is de-energized
allowing atmospheric pressure to enter the pump
cavity, thus permitting the spring to drive the dia-
phragm which forces air out of the pump cavity and
into the vent system. When the solenoid is energized
and de energized, the cycle is repeated creating flow
in typical diaphragm pump fashion. The pump is con-
trolled in 2 modes:
Pump Mode: The pump is cycled at a fixed rate to
achieve a rapid pressure build in order to shorten the
overall test length.
Test Mode: The solenoid is energized with a fixed
duration pulse. Subsequent fixed pulses occur when
the diaphragm reaches the Switch closure point.
The spring in the pump is set so that the system
will achieve an equalized pressure of about 7.5º H20.
The cycle rate of pump strokes is quite rapid as the
system begins to pump up to this pressure. As the
pressure increases, the cycle rate starts to drop off. If
there is no leak in the system, the pump would even-
tually stop pumping at the equalized pressure. If
there is a leak, it will continue to pump at a rate rep-
resentative of the flow characteristic of the size of the
leak. From this information we can determine if the
leak is larger than the required detection limit (cur-
rently set at .040º orifice by CARB). If a leak is
revealed during the leak test portion of the test, the
test is terminated at the end of the test mode and no
further system checks will be performed.
After passing the leak detection phase of the test,
system pressure is maintained by turning on the
LDP's solenoid until the purge system is activated.
Purge activation in effect creates a leak. The cycle
rate is again interrogated and when it increases due
to the flow through the purge system, the leak check
portion of the diagnostic is complete.
The canister vent valve will unseal the system
after completion of the test sequence as the pump
diaphragm assembly moves to the full travel position.
Evaporative system functionality will be verified by
using the stricter evap purge flow monitor. At an
appropriate warm idle the LDP will be energized to
seal the canister vent. The purge flow will be clocked
up from some small value in an attempt to see a
shift in the 02 control system. If fuel vapor, indicated
by a shift in the 02 control, is present the test is
passed. If not, it is assumed that the purge system isnot functioning in some respect. The LDP is again
turned off and the test is ended.
MISFIRE MONITOR
Excessive engine misfire results in increased cata-
lyst temperature and causes an increase in HC emis-
sions. Severe misfires could cause catalyst damage.
To prevent catalytic convertor damage, the PCM
monitors engine misfire.
The Powertrain Control Module (PCM) monitors
for misfire during most engine operating conditions
(positive torque) by looking at changes in the crank-
shaft speed. If a misfire occurs the speed of the
crankshaft will vary more than normal.
FUEL SYSTEM MONITOR
To comply with clean air regulations, vehicles are
equipped with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide. The catalyst works best
when the Air Fuel (A/F) ratio is at or near the opti-
mum of 14.7 to 1.
The PCM is programmed to maintain the optimum
air/fuel ratio of 14.7 to 1. This is done by making
short term corrections in the fuel injector pulse width
based on the O2S sensor output. The programmed
memory acts as a self calibration tool that the engine
controller uses to compensate for variations in engine
specifications, sensor tolerances and engine fatigue
over the life span of the engine. By monitoring the
actual fuel-air ratio with the O2S sensor (short term)
and multiplying that with the program long-term
(adaptive) memory and comparing that to the limit,
it can be determined whether it will pass an emis-
sions test. If a malfunction occurs such that the PCM
cannot maintain the optimum A/F ratio, then the
MIL will be illuminated.
CATALYST MONITOR
To comply with clean air regulations, vehicles are
equipped with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide.
Normal vehicle miles or engine misfire can cause a
catalyst to decay. This can increase vehicle emissions
and deteriorate engine performance, driveability and
fuel economy.
The catalyst monitor uses dual oxygen sensors
(O2S's) to monitor the efficiency of the converter. The
dual O2S's sensor strategy is based on the fact that
as a catalyst deteriorates, its oxygen storage capacity
and its efficiency are both reduced. By monitoring
the oxygen storage capacity of a catalyst, its effi-
ciency can be indirectly calculated. The upstream
O2S is used to detect the amount of oxygen in the
exhaust gas before the gas enters the catalytic con-
DREMISSIONS CONTROL 25 - 3
EMISSIONS CONTROL (Continued)

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.
DESCRIPTION - TRIP DEFINITION
The term ªTripº has different meanings depending
on what the circumstances are. If the MIL (Malfunc-
tion Indicator Lamp) is OFF, a Trip is defined as
when the Oxygen Sensor Monitor and the Catalyst
Monitor have been completed in the same drive cycle.
When any Emission DTC is set, the MIL on the
dash is turned ON. When the MIL is ON, it takes 3
good trips to turn the MIL OFF. In this case, it
depends on what type of DTC is set to know what a
ªTripº is.
For the Fuel Monitor or Mis-Fire Monitor (contin-
uous monitor), the vehicle must be operated in the
ªSimilar Condition Windowº for a specified amount of
time to be considered a Good Trip.
If a Non-Contiuous OBDII Monitor fails twice in a
row and turns ON the MIL, re-running that monitor
which previously failed, on the next start-up and
passing the monitor, is considered to be a Good Trip.
These will include the following:
²Oxygen Sensor²Catalyst Monitor
²Purge Flow Monitor
²Leak Detection Pump Monitor (if equipped)
²EGR Monitor (if equipped)
²Oxygen Sensor Heater Monitor
If any other Emission DTC is set (not an OBDII
Monitor), a Good Trip is considered to be when the
Oxygen Sensor Monitor and Catalyst Monitor have
been completed; or 2 Minutes of engine run time if
the Oxygen Sensor Monitor or Catalyst Monitor have
been stopped from running.
It can take up to 2 Failures in a row to turn on the
MIL. After the MIL is ON, it takes 3 Good Trips to
turn the MIL OFF. After the MIL is OFF, the PCM
will self-erase the DTC after 40 Warm-up cycles. A
Warm-up cycle is counted when the ECT (Engine
Coolant Temperature Sensor) has crossed 160ÉF and
has risen by at least 40ÉF since the engine has been
started.
DESCRIPTION - COMPONENT MONITORS
There are several components that will affect vehi-
cle emissions if they malfunction. If one of these com-
ponents malfunctions the Malfunction Indicator
Lamp (MIL) will illuminate.
Some of the component monitors are checking for
proper operation of the part. Electrically operated
components now have input (rationality) and output
(functionality) checks. Previously, a component like
the Throttle Position sensor (TPS) was checked by
the PCM for an open or shorted circuit. If one of
these conditions occurred, a DTC was set. Now there
is a check to ensure that the component is working.
This is done by watching for a TPS indication of a
greater or lesser throttle opening than MAP and
engine rpm indicate. In the case of the TPS, if engine
vacuum is high and engine rpm is 1600 or greater,
and the TPS indicates a large throttle opening, a
DTC will be set. The same applies to low vacuum if
the TPS indicates a small throttle opening.
All open/short circuit checks, or any component
that has an associated limp-in, will set a fault after 1
trip with the malfunction present. Components with-
out an associated limp-in will take two trips to illu-
minate the MIL.
OPERATION
OPERATION
The Powertrain Control Module (PCM) monitors
many different circuits in the fuel injection, ignition,
emission and engine systems. If the PCM senses a
problem with a monitored circuit often enough to
indicate an actual problem, it stores a Diagnostic
Trouble Code (DTC) in the PCM's memory. If the
25 - 4 EMISSIONS CONTROLDR
EMISSIONS CONTROL (Continued)