Dtc Types - Isuzu 1999 RODEO Workshop Manual

6E1–32
RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION
f When the MIL remains ON while the engine is
running, or when a malfunction is suspected due to a
driveability or emissions problem, a Powertrain
On–Board Diagnostic (OBD) System Check must be
performed. The procedures for these checks are
given in On–Board Diagnostic (OBD II) 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:
f Type A
f Emissions related
f Requests illumination of the MIL of the first trip with a
fail
f Stores a History DTC on the first trip with a fail
f Stores a Freeze Frame (if empty)
f Stores a Fail Record
f Updates the Fail Record each time the diagnostic
test fails
f Type B
f Emissions related
f "Armed" after one (1) trip with a fail
f "Disarmed" after one (1) trip with a pass
f Requests illumination of the MIL on the second
consecutive trip with a fail
f Stores a History DTC on the second consecutive trip
with a fail (The DTC will be armed after the first fail)
f Stores a Freeze Frame on the second consecutive
trip with a fail (if empty)
f Stores a Fail Record when the first test fails (not
dependent on consecutive trip fails)
f Updates the Fail Record each time the diagnostic
test fails
(Some special conditions apply to misfire and fuel trim
DTCs)
f Type C (if the vehicle is so equipped)
f Non–Emissions related
f Requests illumination of the Service Lamp or the
service message on the Drive Information Center
(DIC) on the first trip with a fail
f Stores a History DTC on the first trip with a fail
f Does not store a Freeze Frame
f Stores Fail Record when test fails
f Updates the Fail Record each time the diagnostic
test fails
f Type D. ( Type D non–emissions related are not
utilized on certain vehicle applications).
f Non–Emissions related
f Does not request illumination of any lamp
f Stores a History DTC on the first trip with a fail
f Does not store a Freeze Frame
f Stores Fail Record when test fails
f Updates the Fail Record each time the diagnostic
test fails
IMPORTANT: Only four Fail Records can be stored.
Each Fail Record is for a different DTC. It is possible that
there will not be Fail Records for every DTC if multiple
DTCs are set.
Special Cases of Type B Diagnostic Tests
Unique to the misfire diagnostic, the Diagnostic Executive
has the capability of alerting the vehicle operator to
potentially damaging levels of misfire. If a misfire
condition exists that could potentially damage the
catalytic converter as a result of high misfire levels, the
Diagnostic Executive will command the MIL to "flash" at a
rate of once per second during those the time that the
catalyst damaging misfire condition is present.
Fuel trim and misfire are special cases of Type B
diagnostics. Each time a fuel trim or misfire malfunction is
detected, engine load, engine speed, and engine coolant
temperature are recorded.
When the ignition is turned OFF, the last reported set of
conditions remain stored. During subsequent ignition
cycles, the stored conditions are used as a reference for
similar conditions. If a malfunction occurs during two
consecutive trips, the Diagnostic Executive treats the
failure as a normal Type B diagnostic, and does not use
the stored conditions. However, if a malfunction occurs on
two non–consecutive trips, the stored conditions are
compared with the current conditions. The MIL will then
illuminate under the following conditions:
f When the engine load conditions are within 10% of
the previous test that failed.
f Engine speed is within 375 rpm, of the previous test
that failed.
f Engine coolant temperature is in the same range as
the previous test that failed.
Storing and Erasing Freeze Frame Data and Failure
Records
Government regulations require that engine operating
conditions be captured whenever the MIL is illuminated.
The data captured is called Freeze Frame data. The
Freeze Frame data is very similar to a single record of
operating conditions. Whenever the MIL is illuminated,
the corresponding record of operating conditions is
recorded to the Freeze Frame buffer.
Freeze Frame data can only be overwritten with data
associated with a misfire or fuel trim malfunction. Data
from these faults take precedence over data associated
with any other fault. The Freeze Frame data will not be
erased unless the associated history DTC is cleared.
Each time a diagnostic test reports a failure, the current
engine operating conditions are recorded in the Failure
Records buffer. A subsequent failure will update the
recorded operating conditions. The following operating
conditions for the diagnostic test which failed typically
include the following parameters:
f Air Fuel Ratio
f Air Flow Rate