catalytic converter DODGE RAM 1500 1998 2.G Workshop Manual

PRESSURE TESTER METHOD
The engine should be at normal operating temper-
ature. Recheck the system cold if the cause of coolant
loss is not located during the warm engine examina-
tion.
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING.
Carefully remove the radiator pressure cap from
the filler neck and check the coolant level. Push
down on the cap to disengage it from the stop tabs.
Wipe the inside of the filler neck and examine the
lower inside sealing seat for nicks, cracks, paint, dirt
and solder residue. Inspect the radiator-to- reserve/
overflow tank hose for internal obstructions. Insert a
wire through the hose to be sure it is not obstructed.
Inspect the cams on the outside of the filler neck.
If the cams are damaged, seating of the pressure cap
valve and tester seal will be affected.
Attach pressure tester (7700 or an equivalent) to
radiator filler neck.
Operate the tester pump to apply 103.4 kPa (15
psi) pressure to the system. If the hoses enlarge
excessively or bulges while testing, replace as neces-
sary. Observe the gauge pointer and determine the
condition of the cooling system according to following
criteria:
Holds Steady:If the pointer remains steady for
two minutes, serious coolant leaks are not present in
system. However, there could be an internal leakthat does not appear with normal system test pres-
sure. If it is certain that coolant is being lost and
leaks cannot be detected, inspect for interior leakage
or perform Internal Leakage Test. Refer to INTER-
NAL LEAKAGE INSPECTION.
Drops Slowly:Indicates a small leak or seepage
is occurring. Examine all of the connections for seep-
age or slight leakage with a flashlight. Inspect the
radiator, hoses, gasket edges and heater. Seal the
small leak holes with a Sealer Lubricant (or equiva-
lent). Repair the leak holes and inspect the system
again with pressure applied.
Drops Quickly:Indicates that serious leakage is
occurring. Examine the system for external leakage.
If leaks are not visible, inspect for internal leakage.
Large radiator leak holes should be repaired by a
reputable radiator repair shop.
INTERNAL LEAKAGE INSPECTION
Remove the engine oil pan drain plug and drain a
small amount of engine oil. If coolant is present in
the pan, it will drain first because it is heavier than
oil. An alternative method is to operate engine for a
short period to churn the oil. After this is done,
remove the engine dipstick and inspect for water
globules. Also inspect the transmission dipstick for
water globules and transmission fluid cooler for leak-
age.
WARNING: WITH RADIATOR PRESSURE TESTER
TOOL INSTALLED ON RADIATOR, DO NOT ALLOW
PRESSURE TO EXCEED 145 kPa (21 PSI). PRES-
SURE WILL BUILD UP QUICKLY IF A COMBUSTION
LEAK IS PRESENT. TO RELEASE PRESSURE,
ROCK TESTER FROM SIDE TO SIDE. WHEN
REMOVING TESTER, DO NOT TURN TESTER MORE
THAN 1/2 TURN IF SYSTEM IS UNDER PRESSURE.
Operate the engine without the pressure cap on
the radiator until the thermostat opens. Attach a
Pressure Tester to the filler neck. If pressure builds
up quickly it indicates a combustion leak exists. This
is usually the result of a cylinder head gasket leak or
crack in engine. Repair as necessary.
If there is not an immediate pressure increase,
pump the Pressure Tester. Do this until indicated
pressure is within system range of 110 kPa (16 psi).
Fluctuation of the gauge pointer indicates compres-
sion or combustion leakage into cooling system.
Because the vehicle is equipped with a catalytic
converter,do notshort out cylinders to isolate com-
pression leak.
If the needle on dial of the pressure tester does not
fluctuate, race engine a few times to check for an
abnormal amount of coolant or steam. This would be
emitting from exhaust pipe. Coolant or steam from
Fig. 5 Leak Detection Using Black Light - Typical
1 - TYPICAL BLACK LIGHT TOOL
7 - 6 COOLINGDR
COOLING (Continued)

EXHAUST SYSTEM
TABLE OF CONTENTS
page page
EXHAUST SYSTEM
DESCRIPTION
DESCRIPTION........................1
DESCRIPTION - 5.9L DIESEL.............3
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - GAS ENGINE . . . 4
DIAGNOSIS AND TESTING - DIESEL
ENGINE..............................5
SPECIFICATIONS - TORQUE...............5
SPECIAL TOOLS........................6
CATALYTIC CONVERTER
DESCRIPTION - CATALYTIC CONVERTER.....6
OPERATION............................6
REMOVAL
REMOVAL............................6
REMOVAL............................6
INSPECTION...........................6
INSTALLATION
INSTALLATION........................6
INSTALLATION........................7
EXHAUST PIPE
REMOVAL - 3.7L/4.7L/5.7L.................7
INSPECTION...........................7
INSTALLATION - 3.7L/4.7L/5.7L..............7
EXHAUST PIPE
REMOVAL - DIESEL......................7
INSPECTION...........................8
INSTALLATION - DIESEL..................8
HEAT SHIELDS
DESCRIPTION..........................8
REMOVAL.............................8
INSTALLATION..........................8
MUFFLER
REMOVAL.............................9INSTALLATION..........................9
MUFFLER - 5.9L DIESEL
REMOVAL.............................10
INSTALLATION.........................10
TAILPIPE - 5.9L DIESEL
REMOVAL.............................10
INSPECTION..........................10
INSTALLATION.........................11
TAILPIPE
REMOVAL.............................11
INSPECTION..........................11
INSTALLATION.........................11
TURBOCHARGER SYSTEM
DIAGNOSIS AND TESTING -
TURBOCHARGER BOOST PRESSURE.....11
TURBOCHARGER
DESCRIPTION.........................12
OPERATION...........................13
REMOVAL.............................14
CLEANING............................15
INSPECTION..........................15
INSTALLATION.........................15
CHARGE AIR COOLER AND PLUMBING
DESCRIPTION.........................16
OPERATION...........................16
DIAGNOSIS AND TESTING - CHARGE AIR
COOLER SYSTEM - LEAKS..............16
REMOVAL.............................17
CLEANING............................17
INSPECTION..........................17
INSTALLATION.........................17
EXHAUST SYSTEM
DESCRIPTION
DESCRIPTION
CAUTION: Avoid application of rust prevention com-
pounds or undercoating materials to exhaust sys-
tem floor pan exhaust heat shields. Light overspray
near the edges is permitted. Application of coating
will result in excessive floor pan temperatures and
objectionable fumes.The federal gasoline engine exhaust system con-
sists of engine exhaust manifolds, exhaust pipes, cat-
alytic converter(s), extension pipe (if needed),
exhaust heat shields, muffler and exhaust tailpipe
(Fig. 1), (Fig. 2), (Fig. 3)
The California emission vehicles exhaust system
also contains the above components as well as mini
catalytic converters added to the exhaust pipe.
The exhaust system must be properly aligned to
prevent stress, leakage and body contact. Minimum
clearance between any exhaust component and the
body or frame is 25.4 mm (1.0 in.). If the system con-
tacts any body panel, it may amplify objectionable
noises from the engine or body.
DREXHAUST SYSTEM 11 - 1

Fig. 1 Exhaust System - 3.7L Engine - Typical
1 - CATALYTIC CONVERTER
2 - TORCA CLAMP
3 - INSULATOR4 - MUFFLER
5 - TAILPIPE
Fig. 2 Exhaust System 4.7L Engine - Typical
1 - CATALYTIC CONVERTER
2 - TORCA CLAMP
3 - EXTENSION PIPE4 - INSULATOR
5 - MUFFLER
6 - TAILPIPE/RESONATOR
11 - 2 EXHAUST SYSTEMDR
EXHAUST SYSTEM (Continued)

DESCRIPTION - 5.9L DIESEL
CAUTION: Avoid application of rust prevention com-
pounds or undercoating materials to exhaust sys-
tem floor pan exhaust heat shields. Light overspray
near the edges is permitted. Application of coating
will result in excessive floor pan temperatures and
objectionable fumes.
The diesel engine exhaust system consists of an
engine exhaust manifold, turbocharger, exhaust pipe,
resonator, extension pipe, muffler and exhaust
tailpipe.California emission vehicles include a catalytic con-
verter.
The exhaust system must be properly aligned to
prevent stress, leakage and body contact. The
exhaust components should be kept a minimum of
25.4 mm (1.0 in.) away from the body and frame. If
the system contacts any body panel, it may amplify
objectionable noises from the engine or body.
Fig. 3 Exhaust System 5.7L Engine - Typical
1 - CATALYTIC CONVERTER
2 - TORCA CLAMP
3 - EXTENSION PIPE4 - INSULATOR
5 - MUFFLER
6 - TAILPIPE/RESONATOR
DREXHAUST SYSTEM 11 - 3
EXHAUST SYSTEM (Continued)

DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - GAS ENGINE
EXHAUST SYSTEM DIAGNOSIS CHART
CONDITION POSSIBLE CAUSE CORRECTION
EXCESSIVE EXHAUST NOISE OR
LEAKING EXHAUST GASES1. Leaks at pipe joints. 1. Tighten clamps/bolts at leaking
joints.
2. Rusted or blown out muffler. 2. Replace muffler. Inspect exhaust
system.
3. Broken or rusted out exhaust
pipe.3. Replace exhaust pipe.
4. Exhaust pipe leaking at manifold
flange.4. Tighten/replace flange attaching
nuts/bolts.
5. Exhaust manifold cracked or
broken.5. Replace exhaust manifold.
6. Leak between exhaust manifold
and cylinder head.6. Tighten exhaust manifold to
cylinder head bolts.
7. Catalytic converter rusted or
blown out.7. Replace catalytic converter assy.
8. Restriction in exhaust system. 8. Remove restriction, if possible.
Replace restricted part if necessary.
CAUTION:
When servicing and replacing exhaust system components, disconnect the oxygen sensor connector(s). Allowing
the exhaust to hang by the oxygen sensor wires will damage the harness and/or sensor.
11 - 4 EXHAUST SYSTEMDR
EXHAUST SYSTEM (Continued)

SPECIAL TOOLS
CATALYTIC CONVERTER
DESCRIPTION - CATALYTIC CONVERTER
WARNING: THE NORMAL OPERATING TEMPERA-
TURE OF THE EXHAUST SYSTEM IS VERY HIGH.
THEREFORE, NEVER WORK AROUND OR ATTEMPT
TO SERVICE ANY PART OF THE EXHAUST SYSTEM
UNTIL IT IS COOLED. SPECIAL CARE SHOULD BE
TAKEN WHEN WORKING NEAR THE CATALYTIC
CONVERTER. THE TEMPERATURE OF THE CON-
VERTER RISES TO A HIGH LEVEL AFTER A SHORT
PERIOD OF ENGINE OPERATION TIME.
CAUTION: DO NOT remove spark plug wires from
plugs or by any other means short out cylinders.
Failure of the catalytic converter can occur due to a
temperature increase caused by unburned fuel
passing through the converter.
The stainless steel catalytic converter body is
designed to last the life of the vehicle. Excessive heat
can result in bulging or other distortion, but exces-
sive heat will not be the fault of the converter. If
unburned fuel enters the converter, overheating may
occur. If a converter is heat-damaged, correct the
cause of the damage at the same time the converter
is replaced. Also, inspect all other components of the
exhaust system for heat damage.
Unleaded gasoline must be used to avoid con-
taminating the catalyst core.
50 State emission vehicles incorporate two mini
catalytic converters located after the exhaust mani-
folds and before the inline catalytic converter.
OPERATION
The catalytic converter captures and burns any
unburned fuel mixture exiting the combustion cham-
bers during the exhaust stroke of the engine. This
process aids in reducing emissions output.
REMOVAL
REMOVAL
WARNING: IF TORCHES ARE USED WHEN WORK-
ING ON THE EXHAUST SYSTEM, DO NOT ALLOW
THE FLAME NEAR THE FUEL LINES.
(1) Raise and support the vehicle.
(2) Saturate the bolts and nuts with heat valve
lubricant. Allow 5 minutes for penetration.
(3) Remove the bolts from the crossover pipe to the
catalytic converter connection.
(4) Disconnect oxygen sensor wiring.
(5) Loosen the nuts from the clamp that hold the
catalytic converter to the exhaust pipe flange connec-
tion.
NOTE: Do not remove nut from T-Bolt. Only remove
nut far enough, so that the T end can be removed
from the clamp.
(6) Remove the T bolt end of the fastener, from the
clamp.
(7) Spread the clamp, and remove the catalytic
converter from the vehicle.
(8) Discard the clamp.
NOTE: The catalytic converter to exhaust manifold
clamp is not reusable. Always use a new clamp
when reinstalling the catalytic converter.
REMOVAL
(1) Raise and support vehicle.
(2) Saturate the bolts and nuts with heat valve
lubricant. Allow 5 minutes for penetration.
(3) Remove clamps and nuts.
(4) Remove the catalytic converter.
INSPECTION
Look at the stainless steel body of the converter,
inspect for bulging or other distortion that could be a
result of overheating. If the converter has a heat
shield attached make sure it is not bent or loose.
If you suspect internal damage to the catalyst, tap-
ping the bottom of the catalyst with a rubber mallet
may indicate a damaged core.
INSTALLATION
INSTALLATION
NOTE: The catalytic converter to exhaust manifold
clamp is not reusable. Always use a new clamp
when reinstalling the catalytic converter.
TURBOCHARGER TESTER 9022
11 - 6 EXHAUST SYSTEMDR
EXHAUST SYSTEM (Continued)

(1) Position the catalytic converter onto the
exhaust pipe flange connection. Tighten the nuts to
28 N´m (250 in. lbs.) torque.
(2) Install the muffler onto the catalytic converter
until the alignment tab is inserted into the align-
ment slot.
(3) Install the exhaust clamp at the muffler and
catalytic converter connection. Tighten the clamp
nuts to 54.2 N´m (40 ft. lbs.) torque.
(4) Connect oxygen sensor wiring.
(5) Lower the vehicle.
(6) Start the engine and inspect for exhaust leaks.
Reair exhaust leaks as necessary.
(7) Check the exhaust system for contact with the
body panels. A minimum of 25.4 mm (1.0 in.) is
required between the exhaust system components
and body/frame parts. Make the necessary adjust-
ments, if needed..
INSTALLATION
(1) Assemble converter and clamps loosely in
place.
(2) Install the exhaust pipe onto exhaust mani-
folds, tighten 31 N´m (23 ft. lbs.).
(3) Tighten all clamp nuts to 52.2 N´m (40 ft. lbs.)
torque.
(4) Lower the vehicle.
(5) Start the engine and inspect for exhaust leaks.
Reair exhaust leaks as necessary.
(6) Check the exhaust system for contact with the
body panels. A minimum of 25.4 mm (1.0 in.) is
required between the exhaust system components
and body/frame parts. Make the necessary adjust-
ments, if needed..
EXHAUST PIPE
REMOVAL - 3.7L/4.7L/5.7L
(1) Raise and support the vehicle.
(2) Saturate the bolts and nuts with heat valve
lubricant. Allow 5 minutes for penetration.
(3) Remove exhaust pipe to manifold bolts, retain-
ers and nuts.
(4) Remove the clamp nuts.
(5) Remove the exhaust pipe (Fig. 4).
INSPECTION
Discard rusted clamps, broken or worn supports
and attaching parts. Replace a component with orig-
inal equipment parts, or equivalent. This will assure
proper alignment with other parts in the system and
provide acceptable exhaust noise levels.
INSTALLATION - 3.7L/4.7L/5.7L
(1) Position the exhaust pipe for proper clearance
with the frame and underbody parts. A minimum
clearance of 25.4 mm (1.0 in.) is required.
(2) Position the exhaust pipe to manifold. Install
the bolts, retainers and nuts. Tighten the nuts to 31
N´m (23 ft. lbs.) torque.
(3) Tighten the clamp nuts to 54.2 N´m (40 ft. lbs.)
torque.
(4) Lower the vehicle.
(5) Start the engine and inspect for exhaust leaks
and exhaust system contact with the body panels.
Adjust the alignment, if needed.
EXHAUST PIPE
REMOVAL - DIESEL
(1) Disconnect the battery negative cables.
(2) Raise and support the vehicle on a hoist.
(3) Saturate the bolts and nuts with heat valve
lubricant. Allow 5 minutes for penetration.
(4) Remove the exhaust pipe-to-extension pipe
clamp. Separate the exhaust pipe and extension pipe.
(5) Remove the exhaust pipe-to-turbocharger elbow
clamp (Fig. 5).
(6) Remove the exhaust pipe from the transmis-
sion support (Fig. 5).
Fig. 4 Exhaust Pipe to Manifold Connection -
Typical
1 - BOLT
2 - RETAINER
3 - EXHAUST MANIFOLD
4 - NUT
5 - EXHAUST PIPE
DREXHAUST SYSTEM 11 - 7
CATALYTIC CONVERTER (Continued)

(4) Install MAP sensor mounting bolts (screws).
Refer to Torque Specifications.
(5) Connect electrical connector.
5.7L V-8
The Manifold Absolute Pressure (MAP) sensor is
mounted to the front of the intake manifold air ple-
num box (Fig. 24).
(1) Clean MAP sensor mounting hole at intake
manifold.
(2) Check MAP sensor o-ring seal for cuts or tears.
(3) Position sensor into manifold.
(4) Rotate sensor 1/4 turn clockwise for installa-
tion.
(5) Connect electrical connector.
OXYGEN SENSOR
DESCRIPTION
The Oxygen Sensors (O2S) are attached to, and
protrude into the vehicle exhaust system. Depending
on the engine or emission package, the vehicle may
use a total of either 2 or 4 sensors.
Federal Emission Packages :Two sensors are
used: upstream (referred to as 1/1) and downstream
(referred to as 1/2). With this emission package, the
upstream sensor (1/1) is located just before the main
catalytic convertor. The downstream sensor (1/2) is
located just after the main catalytic convertor.
California Emission Packages:On this emis-
sions package, 4 sensors are used: 2 upstream
(referred to as 1/1 and 2/1) and 2 downstream
(referred to as 1/2 and 2/2). With this emission pack-
age, the right upstream sensor (2/1) is located in the
right exhaust downpipe just before the mini-catalytic
convertor. The left upstream sensor (1/1) is located in
the left exhaust downpipe just before the mini-cata-
lytic convertor. The right downstream sensor (2/2) is
located in the right exhaust downpipe just after the
mini-catalytic convertor, and before the main cata-
lytic convertor. The left downstream sensor (1/2) is
located in the left exhaust downpipe just after the
mini-catalytic convertor, and before the main cata-
lytic convertor.
REMOVAL
CAUTION: Never apply any type of grease to the
oxygen sensor electrical connector, or attempt any
soldering of the sensor wiring harness.
Refer to (Fig. 26) or (Fig. 27) for typical O2S (oxy-
gen sensor) locations.WARNING: THE EXHAUST MANIFOLD, EXHAUST
PIPES AND CATALYTIC CONVERTER BECOME
VERY HOT DURING ENGINE OPERATION. ALLOW
ENGINE TO COOL BEFORE REMOVING OXYGEN
SENSOR.
(1) Raise and support vehicle.
(2) Disconnect wire connector from O2S sensor.
CAUTION: When disconnecting sensor electrical
connector, do not pull directly on wire going into
sensor.
(3) Remove O2S sensor with an oxygen sensor
removal and installation tool.
(4) Clean threads in exhaust pipe using appropri-
ate tap.
Fig. 26 O2 SENSOR SYSTEM - WITH 4 SENSORS
Fig. 27 O2 SENSOR SYSTEM - WITH 2 SENSORS
1 - POST CATALYST OXYGEN SENSOR (1/3)
2 - PRE-CATALYST OXYGEN SENSOR (1/2)
DRFUEL INJECTION - GAS 14 - 35
MAP SENSOR (Continued)

Immediately after a cold start, between predeter-
mined temperature thresholds limits, the three port
solenoid is briefly energized. This initializes the
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, indicatedby a shift in the 02 control, is present the test is
passed. If not, it is assumed that the purge system is
not functioning in some respect. The LDP is again
turned off and the test is ended.
MISFIRE MONITOR
Excessive engine misfire results in increased cata-
lyst temperature and causes an increase in HC emis-
sions. Severe misfires could cause catalyst damage.
To prevent catalytic convertor damage, the PCM
monitors engine misfire.
The Powertrain Control Module (PCM) monitors
for misfire during most engine operating conditions
(positive torque) by looking at changes in the crank-
shaft speed. If a misfire occurs the speed of the
crankshaft will vary more than normal.
FUEL SYSTEM MONITOR
To comply with clean air regulations, vehicles are
equipped with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide. The catalyst works best
when the Air Fuel (A/F) ratio is at or near the opti-
mum of 14.7 to 1.
The PCM is programmed to maintain the optimum
air/fuel ratio of 14.7 to 1. This is done by making
short term corrections in the fuel injector pulse width
based on the O2S sensor output. The programmed
memory acts as a self calibration tool that the engine
controller uses to compensate for variations in engine
specifications, sensor tolerances and engine fatigue
over the life span of the engine. By monitoring the
actual fuel-air ratio with the O2S sensor (short term)
and multiplying that with the program long-term
(adaptive) memory and comparing that to the limit,
it can be determined whether it will pass an emis-
sions test. If a malfunction occurs such that the PCM
cannot maintain the optimum A/F ratio, then the
MIL will be illuminated.
CATALYST MONITOR
To comply with clean air regulations, vehicles are
equipped with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide.
Normal vehicle miles or engine misfire can cause a
catalyst to decay. 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
DREMISSIONS CONTROL 25 - 3
EMISSIONS CONTROL (Continued)

O2S is used to detect the amount of oxygen in the
exhaust gas before the gas enters the catalytic con-
verter. The PCM calculates the A/F mixture from the
output of the O2S. A low voltage indicates high oxy-
gen content (lean mixture). A high voltage indicates a
low content of oxygen (rich mixture).
When the upstream O2S detects a lean condition,
there is an abundance of oxygen in the exhaust gas.
A functioning converter would store this oxygen so it
can use it for the oxidation of HC and CO. As the
converter absorbs the oxygen, there will be a lack of
oxygen downstream of the converter. The output of
the downstream O2S will indicate limited activity in
this condition.
As the converter loses the ability to store oxygen,
the condition can be detected from the behavior of
the downstream O2S. When the efficiency drops, no
chemical reaction takes place. This means the con-
centration of oxygen will be the same downstream as
upstream. The output voltage of the downstream
O2S copies the voltage of the upstream sensor. The
only difference is a time lag (seen by the PCM)
between the switching of the O2S's.
To monitor the system, the number of lean-to-rich
switches of upstream and downstream O2S's is
counted. The ratio of downstream switches to
upstream switches is used to determine whether the
catalyst is operating properly. An effective catalyst
will have fewer downstream switches than it has
upstream switches i.e., a ratio closer to zero. For a
totally ineffective catalyst, this ratio will be one-to-
one, indicating that no oxidation occurs in the device.
The system must be monitored so that when cata-
lyst efficiency deteriorates and exhaust emissions
increase to over the legal limit, the MIL will be illu-
minated.
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 Sensor
²Catalyst 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.
25 - 4 EMISSIONS CONTROLDR
EMISSIONS CONTROL (Continued)