language ISUZU AXIOM 2002 Service Repair Manual

6E±36
6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
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 Frame Data in this section
for more detailed information.
Failure Records
Failure Records data is an enhancement of the OBD II
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.
System Status and Drive Cycle for
Satisfying Federal Inspection/Maintenance
(I/M 240) Regulations
I/M Ready Status means a signal or flag for each
emission system test that had been set in the PCM. I/M
Ready Status indicates that the vehicle on-board
emissions diagnostics have been run. I/M Ready Status
is not concerned whether the emission system passed or
failed the test, only that on-board diagnosis is complete.
Not all vehicles use all possible I/M flags.
Common OBD II 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:

Misfire

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 in Section 6E 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

high canister purge

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 diagnostics are run
when the vehicle is at operating temperature, some when
the vehicle first starts 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 disabled. 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 enabling 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
the 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

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

Current status information on each diagnostic

System Status (I/M ready)

6E±37
6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
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 no 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 II requires that it illuminate under a
strict set of guide lines.
Basically, the MIL is turned on when the PCM detects a
DTC that will impact 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 emissions
related faults.
If the vehicle is experiencing a misfire malfunction which
may cause damage to the Three-Way Catalytic
Converter (TWC), the MIL will flash once per second.
This will continue until the vehicle is outside of speed and
load conditions which could cause possible catalyst
damage, and the MIL will stop flashing and remain on
steady.
Extinguishing the MIL
When the MIL is on, the Diagnostic Executive will turn off
the MIL after
three(3) 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.
If the MIL was set by either a fuel trim or misfire-related
DTC, additional requirements must be met. In addition to
the requirements stated in the previous paragraph, these
requirements are as follows:

The diagnostic tests that are passed must occur
within 375 RPM of the RPM data stored at the time the
last test failed.

Plus or minus ten (10) percent of the engine load that
was stored at the time the last failed.
Similar engine temperature conditions (warmed up or
warming up ) as those stored at the time the last test
failed.
Meeting these requirements ensures that the fault which
turned on the MIL has been corrected.
The MIL (ªCheck Engineº lamp) is on the instrument
panel and has the following function:

It informs the driver that a fault affects vehicle
emission levels has occurred and that the vehicle
should be taken for service as soon as possible.

As a bulb and system check, the MIL will come ªONº
with the key ªONº and the engine not running. When
the engine is started, the MIL will turn ªOFF.º

When the MIL remains ªONº while the engine is
running, or when a malfunction is suspected due to a
driveability or emissions problem, a Powertrain
On-Board Diagnostic (OBD ll) System Check must be
performed. The procedures for these checks are
given in On-Board Diagnostic (OBD) System Check.
These checks will expose faults which may not be
detected if other diagnostics are performed first.
DTC Types
Each DTC is directly related to a diagnostic test. The
Diagnostic Management System sets DTC based on the
failure of the tests during a trip or trips. Certain tests must
fail two (2) consecutive trips before the DTC is set. The
following are the four (4) types of DTCs and the
characteristics of those codes:

Type A

Emissions related

Requests illumination of the MIL of the first trip with a
fail

Stores a History DTC on the first trip with a fail

Stores a Freeze Frame (if empty)

Stores a Fail Record

Updates the Fail Record each time the diagnostic
test fails

Type B

Emissions related

ªArmedº after one (1) trip with a fail

ªDisarmedº after one (1) trip with a pass

Requests illumination of the MIL on the
second
consecutive trip
with a fail

Stores a History DTC on the second consecutive trip
with a fail (The DTC will be armed after the first fail)

Stores a Freeze Frame on the second consecutive
trip with a fail (if empty)

Stores a Fail Record when the first test fails (not
dependent on
consecutive trip fails)

Updates the Fail Record each time the diagnostic
test fails
(Some special conditions apply to misfire and fuel trim
DTCs)

Type C (if the vehicle is so equipped)

Non-Emissions related

Requests illumination of the Service

Stores a History DTC on the
first trip with a fail