1998 ISUZU TROOPER check engine

6E±2
ENGINE DRIVEABILITY AND EMISSIONS
Primary System-Based Diagnostic 6E±50. . . . . . . . .
Primary System-Based Diagnostic 6E±50. . . . . . .
Fuel Control Heated Oxygen Sensor 6E±50. . . . .
HO2S Heater 6E±50. . . . . . . . . . . . . . . . . . . . . . . . .
Fuel Trim System Monitor Diagnostic
Operation 6E±50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fuel Trim System Monitor Diagnostic
Operation 6E±50. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fuel Trim Cell Diagnostic Weights 6E±50. . . . . . .
On-Board Diagnostic (OBD) System Check 6E±51.
A/C Clutch Control Circuit Diagnosis 6E±54. . . . . . .
Electronic Ignition System Diagnosis 6E±60. . . . . . .
Fuel Metering System Check 6E±60. . . . . . . . . . . . .
Idle Air Control (IAC) Valve 6E±60. . . . . . . . . . . . . . .
Fuel System Pressure Test 6E±60. . . . . . . . . . . . . . .
Fuel Injector Coil Test Procedure and Fuel
Injector Balance Test Procedure 6E±60. . . . . . . . . .
Knock Sensor Diagnosis 6E±65. . . . . . . . . . . . . . . . .
Powertrain Control Module (PCM) Diagnosis 6E±65
Multiple PCM Information Sensor DTCS Set 6E±65
Exhaust Gas Recirculation (EGR) Diagnosis
(For except EXPORT and
SOUTH AFRICA) 6E±68. . . . . . . . . . . . . . . . . . . . . . .
Engine Tech 2 Data Definitions and Ranges 6E±68
Typical Scan Data Values 6E±70. . . . . . . . . . . . . . . .
No Malfunction Indicator Lamp (MIL) 6E±74. . . . . . .
Malfunction Indicator Lamp (MIL) ªONº
Steady 6E±77. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Engine Cranks But Will Not Run 6E±79. . . . . . . . . . .
Fuel System Electrical Test 6E±85. . . . . . . . . . . . . . .
Fuel System Diagnosis 6E±88. . . . . . . . . . . . . . . . . . .
Idle Air Control (IAC) System Check 6E±93. . . . . . .
Knock Sensor (KS) System Check
(Engine Knock, Poor Performance, or Poor
Economy) 6E±95. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exhaust Gas Recirculation (EGR) System
Check 6E±97. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Manifold Absolute Pressure (MAP) Output
Check 6E±99. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PCM Diagnostic Trouble Codes 6E±101. . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0101
MAF System Performance 6E±104. . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0102
MAF Sensor Circuit Low Frequency 6E±107. . . . . .
Diagnostic Trouble Code (DTC) P0103
MAF Sensor Circuit High Frequency 6E±110. . . . . .
Diagnostic Trouble Code (DTC) P0107
MAP Sensor Circuit Low Voltage 6E±112. . . . . . . . . .
Diagnostic Trouble Code (DTC) P0108
MAP Sensor Circuit High Voltage 6E±115. . . . . . . . .
Diagnostic Trouble Code (DTC) P0112
IAT Sensor Circuit Low Voltage 6E±118. . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0113
IAT Sensor Circuit High Voltage 6E±121. . . . . . . . . . Diagnostic Trouble Code (DTC) P0117
ECT Sensor Circuit Low Voltage 6E±124. . . . . . . . . .
Diagnostic Trouble Code (DTC) P0118
ECT Sensor Circuit High Voltage 6E±127. . . . . . . . .
Diagnostic Trouble Code (DTC) P0121
TP System Performance 6E±130. . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0122
TP Sensor Circuit Low Voltage 6E±133. . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0123
TP Sensor Circuit High Voltage 6E±136. . . . . . . . . .
Diagnostic Trouble Code (DTC) P0131
HO2S Circuit Low Voltage Bank 1
Sensor 1 6E±139. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0132
HO2S Circuit High Voltage Bank 1
Sensor 1 6E±142. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0134
HO2S Circuit Insufficient Activity Bank 1
Sensor 1 6E±145. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0151
HO2S Circuit Low Voltage Bank 2
Sensor 1 6E±148. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0152
HO2S Circuit HIGH Voltage Bank 2
Sensor 1 6E±151. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0171
Fuel Trim System Lean Bank 1 6E±154. . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0172
Fuel Trim System Rich Bank 1 6E±158. . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0174
Fuel Trim System Lean Bank 2 6E±162. . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0175
Fuel Trim System Rich Bank 2 6E±166. . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0201
Injector 1 Control Circuit 6E±170. . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0202
Injector 2 Control Circuit 6E±173. . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0203
Injector 3 Control Circuit 6E±176. . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0204
Injector 4 Control Circuit 6E±179. . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0205
Injector 5 Control Circuit 6E±182. . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0206
Injector 6 Control Circuit 6E±185. . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0325
KS Module Circuit 6E±188. . . . . . . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0327
KS Sensor Circuit 6E±190. . . . . . . . . . . . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0336
58X Reference Signal Circuit 6E±193. . . . . . . . . . . . .
Diagnostic Trouble Code (DTC) P0337
CKP Sensor Circuit Low Frequency 6E±195. . . . . . .
Diagnostic Trouble Code (DTC) P0341
CMP Sensor Circuit Performance 6E±198. . . . . . . . .
Diagnostic Trouble Code (DTC) P0342
CMP Sensor Circuit Low 6E±202. . . . . . . . . . . . . . . . .

6E±17 ENGINE DRIVEABILITY AND EMISSIONS
PCM Pinouts
PCM Pinout Table, 32-Way Red Connector ± Row ªAº
TS23344
PINPIN FunctionWire ColorIGN ONENG RUNRefer To
A15 Volt Reference ªAºRED5.0 V5.0 VAppropriate Sensor
A2Knock SensorYEL0.0 V DC
2mV AC0.0 V DC
18mV AC
(at idle)General Description and
Operation, Knock Sensor
A3Not UsedÐÐÐÐ
A4Battery FeedWHTB+B+Chassis Electrical
A5Idle Air Control (IAC) ªAº
HighBLUB+/0.8 VB+/0.8 VGeneral Description and
Operation, IAC
A6IAC ªAº LowBLU/WHTB+/0.8 VB+/0.8 VGeneral Description and
Operation, IAC
A7IAC ªBº LowBLU/BLKB+/0.8 VB+/0.8 VGeneral Description and
Operation, IAC
A8IAC ªBº HighBLU/REDB+/0.8 VB+/0.8 VGeneral Description and
Operation, IAC
A9Automatic Transmission
Fluid (ATF) LampORN/BLUB+B+Automatic Transmission
(4L30E)
A10Winter LampPNK/GRNB+B+Automatic Transmission
(4L30E)
A11Power LampGRY/WHTB+B+Automatic Transmission
(4L30E)
A12Antilock Brake System
(ABS)GRYB+B+Antilock Brake System
A13Malfunction Indicator
(Check Engine or MIL)
LampBLU0.0 VB+Chassis Electrical
A14ªCheck Transmissionº
Lamp Driver (AT)ORN/BLKB+B+Chassis Electrical
Up Shift Lamp Driver (MT)ORN/BLU

6E±29 ENGINE DRIVEABILITY AND EMISSIONS
Engine Component Locator Table
Number
NameLocation
1Linear Exhaust Gas Recirculation (EGR) ValveRear right side of the engine
2Throttle Position (TP) SensorOn the rear of the throttle body
3Intake Air Temperature (IAT) SensorOn the intake air duct near the throttle body
4Check Engine (MIL) LightOn the instrument panel beneath the
tachometer
5Positive Crankcase Ventilation (PCV) ValveOn the left of the cylinder head cover
6Air CleanerLeft front of the engine bay
7Mass Air Flow (MAF) SensorAttached to the air filter box
8Camshaft Position (CMP) SensorOn the rear right side at the left of the cylinder
head cover
9Fuel Pressure RegulatorRear right side of the engine
10Idle Air Control (IAC) ValveOn the left of the throttle body
11Upper Intake ManifoldTop of the engine
12Fuse/Relay BoxAlong the inside of the right fender
13Manifold Absolute Pressure (MAP) SensorBolted to the top of the upper intake manifold
14Throttle BodyBetween the intake air duct and the upper
intake manifold
15Engine Coolant Temperature SensorOn the coolant crossover pipe at the front of
the engine, near the throttle body

6E±31 ENGINE DRIVEABILITY AND EMISSIONS
Engine Component Locator Table
Number
NameLocation
1Linear Exhaust Gas Recirculation (EGR) ValveRear right side of the engine
2Throttle Position (TP) SensorOn the rear of the throttle body
3Intake Air Temperature (IAT) SensorOn the intake air duct near the throttle body
4Check Engine (MIL) LightOn the instrument panel beneath the
tachometer
5Positive Crankcase Ventilation (PCV) ValveOn the left of the cylinder head cover
6Air CleanerLeft front of the engine bay
7Mass Air Flow (MAF) SensorAttached to the air filter box
8Camshaft Position (CMP) SensorOn the rear right side at the left of the cylinder
head cover
9Fuel Pressure RegulatorRear right side of the engine
10Idle Air Control (IAC) ValveOn the left of the throttle body
11Upper Intake ManifoldTop of the engine
12Fuse/Relay BoxAlong the inside of the right fender
13Manifold Absolute Pressure (MAP) SensorBolted to the top of the upper intake manifold
14Throttle BodyBetween the intake air duct and the upper
intake manifold
15Engine Coolant Temperature SensorOn the coolant crossover pipe at the front of
the engine, near the throttle body

6E±37 ENGINE DRIVEABILITY AND EMISSIONS
Diagnosis
Strategy-Based Diagnostics
Strategy-Based Diagnostics
The strategy-based diagnostic is a uniform approach to
repair all Electrical/Electronic (E/E) systems. The
diagnostic flow can always be used to resolve an E/E
system problem and is a starting point when repairs are
necessary. The following steps will instruct the technician
how to proceed with a diagnosis:
1. Verify the customer complaint.

To verify the customer complaint, the technician
should know the normal operation of the system.
2. Perform preliminary checks.

Conduct a thorough visual inspection.

Review the service history.

Detect unusual sounds or odors.

Gather diagnostic trouble code information to
achieve an effective repair.
3. Check bulletins and other service information.

This includes videos, newsletters, etc.
4. Refer to service information (manual) system
check(s).

ªSystem checksº contain information on a system
that may not be supported by one or more DTCs.
System checks verify proper operation of the
system. This will lead the technician in an
organized approach to diagnostics.
5. Refer to service diagnostics.
DTC Stored
Follow the designated DTC chart exactly to make an
effective repair.
No DTC
Select the symptom from the symptom tables. Follow the
diagnostic paths or suggestions to complete the repair.
You may refer to the applicable component/system check
in the system checks.
No Matching Symptom
1. Analyze the complaint.
2. Develop a plan for diagnostics.
3. Utilize the wiring diagrams and the theory of
operation.
Call technical assistance for similar cases where repair
history may be available. Combine technician knowledge
with efficient use of the available service information.
Intermittents
Conditions that are not always present are called
intermittents. To resolve intermittents, perform the
following steps:
1. Observe history DTCs, DTC modes, and freezeframe
data.
2. Evaluate the symptoms and the conditions described
by the customer.3. Use a check sheet or other method to identify the
circuit or electrical system component.
4. Follow the suggestions for intermittent diagnosis
found in the service documentation.
Most Tech 2s, such as the Tech II and the
5±8840±0285±0 (Fluke model 87 DVOM), have
data-capturing capabilities that can assist in detecting
intermittents.
No Trouble Found
This condition exists when the vehicle is found to operate
normally. The condition described by the customer may
be normal. Verify the customer complaint against another
vehicle that is operating normally. The condition may be
intermittent. Verify the complaint under the conditions
described by the customer before releasing the vehicle.
1. Re-examine the complaint.
When the Complaint cannot be successfully found or
isolated, a re-evaluation is necessary. The complaint
should be re-verified and could be intermittent as
defined in
Intermittents, or could be normal.
2. Repair and verify.
After isolating the cause, the repairs should be made.
Validate for proper operation and verify that the
symptom has been corrected. This may involve road
testing or other methods to verify that the complaint
has been resolved under the following conditions:

Conditions noted by the customer.

If a DTC was diagnosed, verify a repair by
duplicating conditions present when the DTC was
set as noted in the Failure Records or Freeze
Frame data.
Verifying Vehicle Repair
Verification of the vehicle repair will be more
comprehensive for vehicles with OBD system
diagnostics. Following a repair, the technician should
perform the following steps:
IMPORTANT:Follow the steps below when you verify
repairs on OBD systems. Failure to follow these steps
could result in unnecessary repairs.
1. Review and record the Failure Records and the
Freeze Frame data for the DTC which has been
diagnosed (Freeze Frame data will only be stored for
an A or B type diagnostic and only if the MIL(ºCheck
Engineº lamp) has been requested).
2. Clear the DTC(S).
3. Operate the vehicle within conditions noted in the
Failure Records and Freeze Frame data.
4. Monitor the DTC status information for the specific
DTC which has been diagnosed until the diagnostic
test associated with that DTC runs.

6E±38
ENGINE DRIVEABILITY AND EMISSIONS
General Service Information
OBD Serviceablity Issues
The list of non-vehicle faults that could affect the
performance of the OBD system has been compiled.
These non-vehicle faults vary from environmental
conditions to the quality of fuel used.
The illumination of the MIL (ªCheck Engineº lamp) due to
a non-vehicle fault could lead to misdiagnosis of the
vehicle, increased warranty expense and customer
dissatisfaction. The following list of non-vehicle faults
does not include every possible fault and may not apply
equally to all product lines.
Fuel Quality
Using fuel with the wrong octane rating for your vehicle
may cause driveability problems. Many of the major fuel
companies advertise that using ªpremiumº gasoline will
improve the performance of your vehicle. Most premium
fuels use alcohol to increase the octane rating of the fuel.
Although alcohol-enhanced fuels may raise the octane
rating, the fuel's ability to turn into vapor in cold
temperatures deteriorates. This may affect the starting
ability and cold driveability of the engine.
Low fuel levels can lead to fuel starvation, lean engine
operation, and eventually engine misfire.
Non-OEM Parts
All of the OBD diagnostics have been calibrated to run
with OEM parts. Something as simple as a
high-performance exhaust system that affects exhaust
system back pressure could potentially interfere with the
operation of the EGR valve and thereby turn on the MIL
(ªCheck Engineº lamp). Small leaks in the exhaust
system near the post catalyst oxygen sensor can also
cause the MIL (ªCheck Engineº lamp) to turn on.
Aftermarket electronics, such as cellular phones,
stereos, and anti-theft devices, may radiate EMI into the
control system if they are improperly installed. This may
cause a false sensor reading and turn on the MIL (ªCheck
Engineº lamp).
Environment
Temporary environmental conditions, such as localized
flooding, will have an effect on the vehicle ignition system.
If the ignition system is rain-soaked, it can temporarily
cause engine misfire and turn on the MIL (ªCheck Engineº
lamp).
Poor Vehicle Maintenance
The sensitivity of OBD diagnostics will cause the MIL
(ªCheck Engineº lamp) to turn on if the vehicle is not
maintained properly. Restricted air filters, fuel filters, and
crankcase deposits due to lack of oil changes or improper
oil viscosity can trigger actual vehicle faults that were not
previously monitored prior to OBD. Poor vehicle
maintenance can not be classified as a ªnon-vehicle
faultº, but with the sensitivity of OBD diagnostics, vehicle
maintenance schedules must be more closely followed.Related System Faults
Many of the OBD system diagnostics will not run if the
PCM detects a fault on a related system or component.
One example would be that if the PCM detected a Misfire
fault, the diagnostics on the catalytic converter would be
suspended until Misfire fault was repaired. If the Misfire
fault was severe enough, the catalytic converter could be
damaged due to overheating and would never set a
Catalyst DTC until the Misfire fault was repaired and the
Catalyst diagnostic was allowed to run to completion. If
this happens, the customer may have to make two trips to
the dealership in order to repair the vehicle.
Maintenance Schedule
Refer to the Maintenance Schedule.
Visual / Physical Engine Compartment
Inspection
Perform a careful visual and physical engine
compartment inspection when performing any diagnostic
procedure or diagnosing the cause of an emission test
failure. This can often lead to repairing a problem without
further steps. Use the following guidelines when
performing a visual/physical inspection:

Inspect all vacuum hoses for punches, cuts,
disconnects, and correct routing.

Inspect hoses that are difficult to see behind other
components.

Inspect all wires in the engine compartment for proper
connections, burned or chafed spots, pinched wires,
contact with sharp edges or contact with hot exhaust
manifolds or pipes.
Basic Knowledge of Tools Required
NOTE: Lack of basic knowledge of this powertrain when
performing diagnostic procedures could result in an
incorrect diagnosis or damage to powertrain
components. Do not attempt to diagnose a powertrain
problem without this basic knowledge.
A basic understanding of hand tools is necessary to effec-
tively use this section of the Service Manual.
Serial Data Communications
Class II Serial Data Communications
This vehicle utilizes the ªClass IIº communication system.
Each bit of information can have one of two lengths: long
or short. This allows vehicle wiring to be reduced by
transmitting and receiving multiple signals over a single
wire. The messages carried on Class II data streams are
also prioritized. If two messages attempt to establish
communications on the data line at the same time, only
the message with higher priority will continue. The device
with the lower priority message must wait. The most
significant result of this regulation is that it provides Tech 2
manufacturers with the capability to access data from any
make or model vehicle that is sold.

6E±39 ENGINE DRIVEABILITY AND EMISSIONS
The data displayed on the other Tech 2 will appear the
same, with some exceptions. Some Tech 2s will only be
able to display certain vehicle parameters as values that
are a coded representation of the true or actual value. For
more information on this system of coding, refer to
Decimal/Binary/Hexadecimal Conversions. On this
vehicle Tech 2 displays the actual values for vehicle
parameters. It will not be necessary to perform any
conversions from coded values to actual values.
On-Board Diagnostic (OBD)
On-Board Diagnostic Tests
A diagnostic test is a series of steps, the result of which is
a pass or fail reported to the diagnostic executive. When
a diagnostic test reports a pass result, the diagnostic
executive records the following data:

The diagnostic test has been completed since the last
ignition cycle.

The diagnostic test has passed during the current
ignition cycle.

The fault identified by the diagnostic test is not
currently active.
When a diagnostic test reports a fail result, the diagnostic
executive records the following data:

The diagnostic test has been completed since the last
ignition cycle.

The fault identified by the diagnostic test is currently
active.

The fault has been active during this ignition cycle.

The operating conditions at the time of the failure.
Remember, a fuel trim DTC may be triggered by a list of
vehicle faults. Make use of all information available (other
DTCs stored, rich or lean condition, etc.) when
diagnosing a fuel trim fault.
Comprehensive Component Monitor
Diagnostic Operation
Input Components:
Input components are monitored for circuit continuity and
out-of-range values. This includes rationality checking.
Rationality checking refers to indicating a fault when the
signal from a sensor does not seem reasonable, i.e.
Throttle Position (TP) sensor that indicates high throttle
position at low engine loads or MAP voltage. Input
components may include, but are not limited to the
following sensors:

Vehicle Speed Sensor (VSS)

Crankshaft Position (CKP) sensor

Knock Sensor (KS)

Throttle Position (TP) sensor

Engine Coolant Temperature (ECT) sensor

Camshaft Position (CMP) sensor

Manifold Absolute Pressure (MAP) sensor

Mass Air Flow (MAF) sensorIn addition to the circuit continuity and rationality check,
the ECT sensor is monitored for its ability to achieve a
steady state temperature to enable closed loop fuel
control.
Output Components:
Output components are diagnosed for proper response to
control module commands. Components where
functional monitoring is not feasible will be monitored for
circuit continuity and out-of-range values if applicable.
Output components to be monitored include, but are not
limited to, the following circuits:

Idle Air Control (IAC) Motor

Electronic Transmission controls

A/C relays

Cooling fan relay

VSS output

MIL control

Cruise control inhibit
Refer to PCM and Sensors in General Descriptions.
Passive and Active Diagnostic Tests
A passive test is a diagnostic test which simply monitors a
vehicle system or component. Conversely, an active test,
actually takes some sort of action when performing
diagnostic functions, often in response to a failed passive
test. For example, the EGR diagnostic active test will
force the EGR valve open during closed throttle decel
and/or force the EGR valve closed during a steady state.
Either action should result in a change in manifold
pressure.
Intrusive Diagnostic Tests
This is any on-board test run by the Diagnostic
Management System which may have an effect on
vehicle performance or emission levels.
Warm-Up Cycle
A warm-up cycle means that engine at temperature must
reach a minimum of 70
C (160
F) and rise at least 22
C
(40
F) over the course of a trip.
Freeze Frame
Freeze Frame is an element of the Diagnostic
Management System which stores various vehicle
information at the moment an emissions-related fault is
stored in memory and when the MIL is commanded on.
These data can help to identify the cause of a fault. Refer
to
Storing And Erasing Freeze Fame Data for more
detailed information.
Failure Records
Failure Records data is an enhancement of the OBD
Freeze Frame feature. Failure Records store the same
vehicle information as does Freeze Frame, but it will store
that information for any fault which is stored in on-board
memory, while Freeze Frame stores information only for
emission-related faults that command the MIL on.

6E±40
ENGINE DRIVEABILITY AND EMISSIONS
Common OBD Terms
Diagnostic
When used as a noun, the word diagnostic refers to any
on-board test run by the vehicle's Diagnostic
Management System. A diagnostic is simply a test run on
a system or component to determine if the system or
component is operating according to specification. There
are many diagnostics, shown in the following list:

Oxygen sensors

Oxygen sensor heaters

EGR

Catalyst monitoring
Enable Criteria
The term ªenable criteriaº is engineering language for the
conditions necessary for a given diagnostic test to run.
Each diagnostic has a specific list of conditions which
must be met before the diagnostic will run. ªEnable
criteriaº is another way of saying ªconditions requiredº.
The enable criteria for each diagnostic is listed on the first
page of the DTC description under the heading
ªConditions for Setting the DTCº. Enable criteria varies
with each diagnostic, and typically includes, but is not
limited to the following items:

engine speed

vehicle speed

ECT

MAF/MAP

barometric pressure

IAT

TP

fuel trim

TCC enabled

A/C on
Trip
Technically, a trip is a key on-run-key off cycle in which all
the enable criteria for a given diagnostic are met, allowing
the diagnostic to run. Unfortunately, this concept is not
quite that simple. A trip is official when all the enable
criteria for a given diagnostic are met. But because the
enable criteria vary from one diagnostic to another, the
definition of trip varies as well. Some diagnostic are run
when the vehicle is at operating temperature, some when
the vehicle first start up; some require that the vehicle be
cruising at a steady highway speed, some run only when
the vehicle is idle; some diagnostics function with the
TCC disables. Some run only immediately following a
cold engine start-up.
A trip then, is defined as a key on-run-key off cycle in
which the vehicle was operated in such a way as to satisfy
the enables criteria for a given diagnostic, and this
diagnostic will consider this cycle to be one trip. However,
another diagnostic with a different set of enable criteria
(which were not met) during this driving event, would not
consider it a trip. No trip will occur for that particular
diagnostic until the vehicle is driven in such a way as to
meet all the enable criteria.
The Diagnostic Executive
The Diagnostic Executive is a unique segment of
software which is designed to coordinate and prioritize
the diagnostic procedures as well as define the protocol
for recording and displaying their results. The main
responsibilities of the Diagnostic Executive are listed as
following:

Commanding the MIL (ªCheck Engineº lamp) on and
off

DTC logging and clearing

Freeze Frame data for the first emission related DTC
recorded

Non-emission related Service Lamp (future)

Operating conditions Failure Records buffer, (the
number of records will vary)

Current status information on each diagnostic
The Diagnostic Executive records DTCs and turns on the
MIL when emission-related faults occur. It can also turn
off the MIL if the conditions cease which caused the DTC
to set.
Diagnostic Information
The diagnostic charts and functional checks are designed
to locate a faulty circuit or component through a process
of logical decisions. The charts are prepared with the
requirement that the vehicle functioned correctly at the
time of assembly and that there are not multiple faults
present.
There is a continuous self-diagnosis on certain control
functions. This diagnostic capability is complemented by
the diagnostic procedures contained in this manual. The
language of communicating the source of the malfunction
is a system of diagnostic trouble codes. When a
malfunction is detected by the control module, a
diagnostic trouble code is set and the Malfunction
Indicator Lamp (MIL) (ªCheck Engineº lamp) is
illuminated.
Malfunction Indicator Lamp (MIL)
The Malfunction Indicator Lamp (MIL) looks the same as
the MIL you are already familiar with (ªCheck Engineº
lamp). However, OBD requires that the it illuminate under
a strict set of guide lines.
Basically, the MIL is turned on when the PCM detects a
DTC that will impact the vehicle emissions.
The MIL is under the control of the Diagnostic Executive.
The MIL will be turned on if an emissions-related
diagnostic test indicates a malfunction has occurred. It
will stay on until the system or component passes the
same test, for three consecutive trips, with no
emissionsrelated faults.
Extinguishing the MIL
When the MIL is on, the Diagnostic Executive will turn off
the MIL after
three consecutive trips that a ªtest passedº
has been reported for the diagnostic test that originally
caused the MIL to illuminate.
Although the MIL has been turned off, the DTC will remain
in the PCM memory (both Freeze Frame and Failure
Records) until
forty(40) warm-up cycles after no faults
have been completed.