The Diagnostic Executive - Isuzu 1999 RODEO Workshop Manual

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 at 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
follows:
f Commanding the MIL ("Check Engine" lamp) ON and
OFF
f DTC logging and clearing
f Freeze Frame data for the first emission related DTC
recorded
f Non–emission related Service Lamp (future)
f Operating conditions Failure Records buffer, (the
number of records will vary)
f Current status information on each diagnostic
f System Status (I/M ready)
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.
RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION
There is a continuous self–diagnosis on certain control
functions. This diagnostic capability is complimented 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) ("Check Engine" lamp) is
illuminated.
Malfunction Indicator Lamp (MIL)
The Malfunction Indicator Lamp (MIL) looks the same as
the MIL you are already familiar with ("Check Engine"
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 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
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 "test
passed" 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:
f The diagnostic tests that are passed must occur with
375 RPM of the RPM data stored at the time the last
test failed.
f Plus or minus ten (10) percent of the engine load that
was stored at the time the last test failed.
f 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 ("Check Engine" lamp) is on the instrument panel
and has the following functions:
f It informs the driver that a fault that affects vehicle
emission levels has occurred and that the vehicle
should be taken for service as soon as possible.
f As a bulb and system check, the MIL will come ON
with the key ON and the engine not running. When the
engine is started, the MIL will turn OFF.
6E1–31