sensor CHRYSLER VOYAGER 1996 Service Manual

Adaptive Fuel Factor
Barometric Pressure
Engine Speed
Module Spark Advance
Speed Control Target
Intake Air Temp Degrees
Intake Air Temp Volts
Charging System Goal
Theft Alarm Status
Map Sensor Voltage
Vehicle Speed
Throttle Opening (percentage)
TPS Calculated
Cam Timing Position
Target Idle
Time From Start To Run
Run Time At Stall
Injector Pulse-width
Upstream O2S Volts
Downstream O2S Volts
Closed Loop Timer
Short Term Adaptive
Current Adaptive Cell
Adaptive Memory Cell 0
Adaptive Memory Cell 1
Adaptive Memory Cell 2
Adaptive Memory Cell 3
Adaptive Memory Cell 4
Adaptive Memory Cell 5
Adaptive Memory Cell 6
Adaptive Memory Cell 7
Adaptive Memory Cell 8
Adaptive Memory Cell 9
Adaptive Memory Cell 10
Adaptive Memory Cell 11
Adaptive Memory Cell 12
Adaptive Memory Cell 13
Adaptive Memory Cell 14
Adaptive Memory Cell 15
Purge Free Idle Cell
Purge Free Cell 2 (corresponds to memory cell 2)
Purge Free Cell 3 (corresponds to memory cell 5)
Target IAC Steps
Retard Cylinder (1)
Retard Cylinder (2)
Retard Cylinder (3)
Retard Cylinder (4)
Retard Cylinder (5)
Retard Cylinder (6)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.
DIAGNOSTIC TROUBLE CODES
A Diagnostic Trouble Code (DTC) indicates the
PCM has recognized an abnormal condition in the
system.
The preferred and most accurate method of retriev-
ing a DTC is by using the DRB scan tool. The scan
tool supplies detailed diagnostic information which
can be used to more accurately diagnose causes for a
DTC.
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.
NOTE: For a list of DTC's, refer to the charts in this
section.
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) 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.
(2) Turn the ignition switch on and access the
ªRead Faultº screen.
(3) Record all the DTC's and ªfreeze frameº infor-
mation shown on the DRB scan tool.
(4) 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.
NSEMISSION CONTROL SYSTEMS 25 - 3
DESCRIPTION AND OPERATION (Continued)

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

HEX
CODEGENERIC
SCAN
TOOL
CODEDRB SCAN TOOL
DISPLAYDESCRIPTION OF DIAGNOSTIC
TROUBLE CODE
20 P0134 Right Rear (or just) Upstream O2S
Stays at CenterNeither rich or lean condition detected from the
oxygen sensor.
21* Engine Is Cold Too Long Engine did not reach operating temperature within
acceptable limits.
23 P0500 No Vehicle Speed Sensor Signal No vehicle speed sensor signal detected during
road load conditions.
24 P0107 MAP Sensor Voltage Too Low MAP sensor input below minimum acceptable
voltage.
25 P0108 MAP Sensor Voltage Too High MAP sensor input above maximum acceptable
voltage.
27 P1297 No Change in MAP From Start to
RunNo difference recognized between the engine MAP
reading and the barometric (atmospheric) pressure
reading from start-up.
28* No Crank Reference Signal at PCM No crank reference signal detected during engine
cranking.
29 P0353 Ignition Coil #3 Primary Circuit Peak primary circuit current not achieved with
maximum dwell time.
2A P0352 Ignition Coil #2 Primary Circuit Peak primary circuit current not achieved with
maximum dwell time.
2B P0351 Ignition Coil #1 Primary Circuit Peak primary circuit current not achieved with
maximum dwell time.
2C* No ASD Relay Output Voltage at
PCMAn Open condition Detected In The ASD Relay
Output Circuit.
2E P0401 EGR System Failure Required change in air/fuel ratio not detected
during diagnostic test.
30* P1697 PCM Failure SRI Miles Not Stored Unsuccessful attempt to update EMR mileage in
the PCM EEPROM.
31 P1698 PCM Failure EEPROM Write
DeniedUnsuccessful attempt to write to an EEPROM
location by the PCM.
39 P0112 Intake Air Temp Sensor Voltage
LowIntake air temperature sensor input below the
maximum acceptable voltage.
3A P0113 Intake Air Temp Sensor Voltage
HighIntake air temperature sensor input above the
minimum acceptable voltage.
3C P0106 Barometric Pressure Out Of Range MAP sensor has a baro reading below an
acceptable value.
3D P0204 Injector #4 Control Circuit Injector #4 output driver does not respond properly
to the control signal.
3E P0132 Right Rear (or just) Upstream O2S
Shorted to VoltageOxygen sensor input voltage maintained above the
normal operating range.
44 P0600 PCM Failure SPI Communications PCM Internal fault condition detected.
45 P0205 Injector #5 Control Circuit Injector #5 output driver does not respond properly
to the control signal.
46 P0206 Injector #6 Control Circuit Injector #6 output driver does not respond properly
to the control signal.
NSEMISSION CONTROL SYSTEMS 25 - 5
DESCRIPTION AND OPERATION (Continued)

HEX
CODEGENERIC
SCAN
TOOL
CODEDRB SCAN TOOL
DISPLAYDESCRIPTION OF DIAGNOSTIC
TROUBLE CODE
52* SPD CTRL PWR RLY; or S/C 12v
Driver CKTMalfunction detected with power feed to speed
control servo solenoids.
5A A/C Pressure Sensor Volts Too
HighSensor input voltage is above 4.9 volts.
5B A/C Pressure Sensor Volts Too Low Sensor input voltage is below .098 volts.
60 P1698 No CCD Messages From TCM No messages received from Transmission Control
Module.
61 No CCD Message From Body
Control ModuleNo messages received from Body Control Module.
65* Fuel Pump Relay Control Circuit An open or shorted condition detected in the fuel
pump relay control circuit.
66 P0133 Right Bank Upstream O2S Slow
ResponseOxygen sensor response slower than minimum
required switching frequency.
67 P0135 Right Rear (or just) Upstream O2S
Heater FailureUpstream oxygen sensor heating element circuit
malfunction.
69 P0141 Right Rear (or just) Downstream
O2S Heater FailureOxygen sensor heating element circuit malfunction.
6A P0300 Multiple Cylinder Mis-fire Misfire detected in multiple cylinders.
6B P0301 Cylinder #1 Mis-fire Misfire detected in cylinder #1.
6C P0302 Cylinder #2 Mis-fire Misfire detected in cylinder #2.
6D P0303 Cylinder #3 Mis-fire Misfire detected in cylinder #3.
6E P0304 Cylinder #4 Mis-fire Misfire detected in cylinder #4.
70 P0420 Right Rear (or just) Catalyst
Efficency FailureCatalyst efficiency below required level.
71* P0441 Evap Purge Flow Monitor Failure Insufficient or excessive vapor flow detected during
evaporative emission system operation.
72 P1899 P/N Switch Stuck in Park or in Gear Incorrect input state detected for the Park/Neutral
switch, auto. trans. only.
76 P0172 Right Rear (or just) Fuel System
RichA rich air/fuel mixture has been indicated by an
abnormally lean correction factor.
77 P0171 Right Rear (or just) Fuel System
LeanA lean air/fuel mixture has been indicated by an
abnormally rich correction factor.
7E P0138 Right Rear (or just) Downstream
O2S Shorted to VoltageOxygen sensor input voltage maintained above the
normal operating range.
80 P0128 Closed Loop Temp Not Reached Engine does not reach 20ÉF within 5 minutes with
a vehicle speed signal.
81 P0140 Right Rear (or just) Downstream
O2S Stays at CenterNeither reich or lean condition detected from the
downstream oxygen sensor.
84 P0121 TPS Voltage Does Not Agree With
MAPTPS signal does not correlate to MAP sensor
89 P0700 EATX Controller DTC Present An automatic transmission input DTC has been set
in the transmission controller. Refer to Group 21.
8A P1294 Target Idle Not Reached Actual idle speed does not equal target idle speed.
25 - 6 EMISSION CONTROL SYSTEMSNS
DESCRIPTION AND OPERATION (Continued)

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

MONITORED SYSTEMS
There are new electronic circuit monitors that
check fuel, emission, engine and ignition perfor-
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 (Check
Engine) Lamp will be illuminated. These monitors
generate Diagnostic Trouble Codes that can be dis-
played with the check engine lamp or a scan tool.
The following is a list of the system monitors:
²EGR Monitor
²Misfire Monitor
²Fuel System Monitor
²Oxygen Sensor Monitor
²Oxygen Sensor Heater Monitor
²Catalyst Monitor
²Evaporative System Leak Detection Monitor
Following is a description of each system monitor,
and its DTC.
Refer to the appropriate Powertrain Diagnos-
tics Procedures manual for diagnostic proce-
dures.
HEX 66, and 7AÐOXYGEN 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 nitrous oxide (NOx) from
the exhaust.
The O2S is also the main sensing element for the
EGR, Catalyst and Fuel Monitors.
The O2S may fail in any or all of the following
manners:
²Slow response rate
²Reduced output voltage
²Dynamic shift
²Shorted or open circuitsResponse 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 to
detect 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.
HEX 67, 69, 7C, and 7DÐOXYGEN SENSOR
HEATER MONITOR
If 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.
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 Éto 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 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 O2S circuit is monitored for a drop in voltage.
The sensor output is used to test the heater by iso-
lating the effect of the heater element on the O2S
output voltage from the other effects.
HEX 2EÐEGR MONITOR
The Powertrain Control Module (PCM) performs
an on-board diagnostic check of the EGR system.
The EGR system consists of two main components:
a vacuum solenoid and a vacuum operated valve with
a back pressure transducer. The EGR monitor is used
to test whether the EGR system is operating within
specifications. The diagnostic check activates only
during selected engine/driving conditions. When the
25 - 8 EMISSION CONTROL SYSTEMSNS
DESCRIPTION AND OPERATION (Continued)

conditions are met, the EGR is turned off (solenoid
energized) and the O2S compensation control is mon-
itored. Turning off the EGR shifts the air fuel (A/F)
ratio in the lean direction. The O2S data should indi-
cate an increase in the O2 concentration in the com-
bustion chamber when the exhaust gases are no
longer recirculated. While this test does not directly
measure the operation of the EGR system, it can be
inferred from the shift in the O2S data whether the
EGR system is operating correctly. Because the O2S
is being used, the O2S test must pass its test before
the EGR test.
HEX 6A,6B, 6C, 6D, 6E, AE, and AFÐMISFIRE
MONITOR
Excessive engine misfire results in increased cata-
lyst temperature and causes an increase in HC emis-
sions. Severe misfires could cause catalyst damage.
To prevent catalytic convertor damage, the PCM
monitors engine misfire.
The Powertrain Control Module (PCM) monitors
for misfire during most engine operating conditions
(positive torque) by looking at changes in the crank-
shaft speed. If a misfire occurs the speed of the
crankshaft will vary more than normal.
HEX 76, 77, 78, and 79ÐFUEL SYSTEM
MONITOR
To comply with clean air regulations, vehicles are
equipped with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide. The catalyst works best
when the air fuel (A/F) ratio is at or near the opti-
mum of 14.7 to 1.
The PCM is programmed to maintain the optimum
air/fuel ratio of 14.7 to 1. This is done by making
short term corrections in the fuel injector pulse width
based on the O2S output. The programmed memory
acts as a self calibration tool that the engine control-
ler uses to compensate for variations in engine spec-
ifications, sensor tolerances and engine fatigue over
the life span of the engine. By monitoring the actual
air-fuel ratio with the O2S (short term) and multiply-
ing that with the program long-term (adaptive) mem-
ory and comparing that to the limit, it can be
determined whether it will pass an emissions test. If
a malfunction occurs such that the PCM cannot
maintain the optimum A/F ratio, then the MIL will
be illuminated.
HEX 70, and B4ÐCATALYST MONITOR
To comply with clean air regulations, vehicles are
equipped with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide.Normal vehicle miles or engine misfire can cause a
catalyst to decay. A meltdown of the ceramic core can
cause a reduction of the exhaust passage. This can
increase vehicle emissions and deteriorate engine
performance, driveability and fuel economy.
The catalyst monitor uses dual oxygen sensors
(O2S's) to monitor the efficiency of the converter. The
dual O2Ss strategy is based on the fact that as a cat-
alyst deteriorates, its oxygen storage capacity and its
efficiency are both reduced. By monitoring the oxy-
gen storage capacity of a catalyst, its efficiency can
be indirectly calculated. The upstream O2S is used to
detect the amount of oxygen in the exhaust gas
before the gas enters the catalytic converter. The
PCM calculates the A/F mixture from the output of
the O2S. A low voltage indicates high oxygen content
(lean mixture). A high voltage indicates a low content
of oxygen (rich mixture).
When the upstream O2S detects a lean condition,
there is an abundance of oxygen in the exhaust gas.
A functioning converter would store this oxygen so it
can use it for the oxidation of HC and CO. As the
converter absorbs the oxygen, there will be a lack of
oxygen downstream of the converter. The output of
the downstraem O2S will indicate limited activity in
this condition.
As the converter loses the ability to store oxygen,
the condition can be detected from the behavior of
the downstream O2S. When the efficiency drops, no
chemical reaction takes place. This means the con-
centration of oxygen will be the same downstream as
upstream. The output voltage of the downstream
O2S copies the voltage of the upstream sensor. The
only difference is a time lag (seen by the PCM)
between the switching of the O2S's.
To monitor the system, the number of lean-to-rich
switches of upstream and downstream O2S's is
counted. The ratio of downstream switches to
upstream switches is used to determine whether the
catalyst is operating properly. An effective catalyst
will have fewer downstream switches than it has
upstream switches i.e., a ratio closer to zero. For a
totally ineffective catalyst, this ratio will be one-to-
one, indicating that no oxidation occurs in the device.
The system must be monitored so that when cata-
lyst efficiency deteriorates and exhaust emissions
increase to over the legal limit, the MIL (check
engine lamp) will be illuminated.
HEX A0, A1, B7, and B8ÐLEAK DETECTION
PUMP MONITOR
The leak detection assembly incorporates two pri-
mary functions: it must detect a leak in the evapora-
tive system and seal the evaporative system so the
leak detection test can be run.
NSEMISSION CONTROL SYSTEMS 25 - 9
DESCRIPTION AND OPERATION (Continued)

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
and 1600 rpm.
Any component that has an associated limp in will
set a fault after 1 trip with the malfunction present.
Refer to the Diagnostic Trouble Codes Description
Charts in this section and the appropriate Power-
train Diagnostic Procedure Manual for diagnostic
procedures.
NON-MONITORED CIRCUITS
The PCM does not monitor all circuits, systems
and conditions that could have malfunctions causing
driveability problems. However, problems with these
systems may cause the PCM to store diagnostic trou-
ble codes for other systems or components. For exam-
ple, a fuel pressure problem will not register a fault
directly, but could cause a rich/lean condition or mis-
fire. This could cause the PCM to store an oxygen
sensor or misfire diagnostic trouble code.
The major non-monitored circuits are listed below
along with examples of failures modes that do not
directly cause the PCM to set a DTC, but for a sys-
tem that is monitored.
FUEL PRESSURE
The fuel pressure regulator controls fuel system
pressure. The PCM cannot detect a clogged fuel
pump inlet filter, clogged in-line fuel filter, or a
pinched fuel supply or return line. However, these
could result in a rich or lean condition causing the
PCM to store an oxygen sensor or fuel system diag-
nostic trouble code.
SECONDARY IGNITION CIRCUIT
The PCM cannot detect an inoperative ignition coil,
fouled or worn spark plugs, ignition cross firing, or
open spark plug cables.
CYLINDER COMPRESSION
The PCM cannot detect uneven, low, or high engine
cylinder compression.
EXHAUST SYSTEM
The PCM cannot detect a plugged, restricted or
leaking exhaust system. It may set a EGR or Fuel
system fault or O2S.
FUEL INJECTOR MECHANICAL
MALFUNCTIONS
The PCM cannot determine if a fuel injector is
clogged, the needle is sticking or if the wrong injector
is installed. However, these could result in a rich or
lean condition causing the PCM to store a diagnostic
trouble code for either misfire, an oxygen sensor, or
the fuel system.
EXCESSIVE OIL CONSUMPTION
Although the PCM monitors engine exhaust oxygen
content when the system is in closed loop, it cannot
determine excessive oil consumption.
THROTTLE BODY AIR FLOW
The PCM cannot detect a clogged or restricted air
cleaner inlet or filter element.
VACUUM ASSIST
The PCM cannot detect leaks or restrictions in the
vacuum circuits of vacuum assisted engine control
system devices. However, these could cause the PCM
to store a MAP sensor diagnostic trouble code and
cause a high idle condition.
PCM SYSTEM GROUND
The PCM cannot determine a poor system ground.
However, one or more diagnostic trouble codes may
be generated as a result of this condition. The mod-
ule should be mounted to the body at all times, also
during diagnostic.
PCM CONNECTOR ENGAGEMENT
The PCM may not be able to determine spread or
damaged connector pins. However, it might store
diagnostic trouble codes as a result of spread connec-
tor pins.
HIGH AND LOW LIMITS
The PCM compares input signal voltages from each
input device with established high and low limits for
the device. If the input voltage is not within limits
and other criteria are met, the PCM stores a diagnos-
tic trouble code in memory. Other diagnostic trouble
code criteria might include engine RPM limits or
input voltages from other sensors or switches that
must be present before verifying a diagnostic trouble
code condition.
NSEMISSION CONTROL SYSTEMS 25 - 11
DESCRIPTION AND OPERATION (Continued)

the amount of EGR supplied to the engine. This pro-
vides the correct amount of exhaust gas recirculation
for different operating conditions.
This system does not allow EGR at idle. The EGR
systems can operate at all coolant temperatures
above 60ÉF as long as the battery ambient tempera-
ture is above 7ÉF.
DIAGNOSIS AND TESTING
EGR SYSTEM ON-BOARD DIAGNOSTICS
The PCM performs an on-board diagnostic check of
the EGR system. The diagnostic system uses the
electronic EGR transducer for the system tests.
The diagnostic check activates only during selected
engine/driving conditions. When the conditions are
met, the PCM energizes the transducer solenoid to
disable the EGR. The PCM checks for a change in
the heated oxygen sensor signal. If the air-fuel mix-
ture goes lean, the PCM will attempt to enrichen the
mixture. The PCM registers a Diagnostic Trouble
Code (DTC) if the EGR system is not operating cor-
rectly. After registering a DTC, the PCM turns on the
malfunction indicator (Check Engine) lamp after 2
consecutive trips. There are 2 types of failures sensed
by the PCM. The first is a short or open in the elec-
trical solenoid circuit. The second is a mechanical
failure or loss of vacuum. The Malfunction Indicator
Lamp (MIL) indicates the need for service.
If a problem is indicated by the MIL and a DTC for
the EGR system is set, check for proper operation of
the EGR system. Use the System Test, EGR Gas
Flow Test. If the EGR system tests properly, check
the system using the DRB scan tool. Refer to
On-Board Diagnosis sections in this Group. Also,
refer to the DRB scan tool and the appropriate Pow-
ertrain Diagnostics Procedure manual.
EGR SYSTEM TEST
WARNING: APPLY PARKING BRAKE AND/OR
BLOCK WHEELS BEFORE TESTING THE EGR SYS-
TEM.
(1) Check the condition of all EGR system hoses
and tubes for leaks, cracks, kinks and hardening of
rubber hoses. Repair and correct these conditions
before performing any tests.
(2) Be sure the hoses at both the EGR valve and
EGR valve control are connected to the proper fit-
tings (Fig. 4).
(3) Be sure the electrical connector is firmly con-
nected at the valve control.
(4) To check EGR system operation, connect the
DRB scan tool to the 16±way data link connector.
The data link connector is located on the lower edge
of the instrument panel near the steering column.
Refer to the appropriate Powertrain Diagnostic Pro-
cedures service manual for operation of the DRB
scan tool when diagnosing the EGR system.
(5) After checking the system with the DRB scan
tool, proceed to the following EGR Valve Leakage and
EGR Valve Control Tests and repair as necessary.
Fig. 3 Electric EGR Transducer Assembly
Fig. 4 EGR Value and EGR Value ÐTypical
NSEMISSION CONTROL SYSTEMS 25 - 19
DESCRIPTION AND OPERATION (Continued)

EMISSION CONTROL SYSTEM
CONTENTS
page page
EMISSION CONTROL SYSTEMÐ
2.0L ENGINE.......................... 9
EXHAUST EMISSION CONTROLSÐ
2.5L DIESEL ENGINE................... 5ON-BOARD DIAGNOSTICSÐ
2.5L DIESEL ENGINE................... 1
ON-BOARD DIAGNOSTICSÐ2.5L DIESEL ENGINE
INDEX
page page
GENERAL INFORMATION
SYSTEM DESCRIPTIONÐ
2.5L DIESEL ENGINE................... 1DESCRIPTION AND OPERATION
DIAGNOSTIC TROUBLE CODES............ 2
GENERAL INFORMATION
SYSTEM DESCRIPTIONÐ2.5L DIESEL ENGINE
The 2.5L diesel Powertrain Control Module (PCM)
monitors and controls many different circuits in the
fuel injection pump and engine systems. If the PCM
senses a problem with a monitored circuit that indi-
cates an actual problem, a Diagnostic Trouble Code
(DTC) will be stored in the PCM's memory, and even-
tually will illuminate the Diesel Glow Plug lamp con-
stantly while the key is on. If the problem is
repaired, or is intermittent, the PCM will erase the
DTC after 40 warm-up cycles. A warm-up cycle con-
sists of starting the vehicle when the engine is cold,
then the engine to warms up to a certain tempera-
ture, and finally, the engine temperature falls to a
normal operating temperature, then the key is
turned off.
Certain criteria must be met for a DTC to be
entered into PCM memory. The criteria may be a
specific range of engine rpm, engine or fuel tempera-
ture and/or input voltage to the PCM. A DTC indi-
cates that the PCM has identified an abnormal
signal in a circuit or the system. A DTC may indicate
the result of a failure, but never identify the failed
component directly.
There are several operating conditions that the
PCM does not monitor and set a DTC for. Refer to
the following Monitored Circuits and Non±Monitored
Circuits in this section.
MONITORED CIRCUITS
The PCM can detect certain problems in the elec-
trical system.
Open or Shorted Circuit± The PCM can deter-
mine if sensor output (which is the input to PCM) is
within proper range. It also determines if the circuit
is open or shorted.
Output Device Current Flow± The PCM senses
whether the output devices are electrically connected.
If there is a problem with the circuit, the PCM
senses whether the circuit is open, shorted to ground
(±), or shorted to (+) voltage.
NON±MONITORED CIRCUITS
The PCM does not monitor the following circuits,
systems or conditions that could have malfunctions
that result in driveability problems. A DTC will not
be displayed for these conditions.
Fuel Pressure:Fuel pressure is controlled by the
fuel injection pump. The PCM cannot detect prob-
lems in this component.
Cylinder Compression:The PCM cannot detect
uneven, low, or high engine cylinder compression.
Exhaust System:The PCM cannot detect a
plugged, restricted or leaking exhaust system.
Fuel Injector Malfunctions:The PCM cannot
determine if the fuel injector is clogged, or the wrong
injector is installed. The fuel injectors on the diesel
engine arenot controlledby the PCM, although a
NS/GSEMISSION CONTROL SYSTEM 25 - 1