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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.
Comprehensive Component Monitor Diagnostic
Operation
Comprehensive component monitoring diagnostics are
required to operate the engine properly.
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., accelerator position sensor (APS) that
indicates high throttle position at low engine loads or
low intake air pressure. Input components may include,
but are not limited to the following sensors:
• Intake air temperature (IAT) sensor
• Crank position (CKP) sensor
• Engine coolant temperature (ECT) sensor
• Cam position (CMP) sensor
• Accelerator position (AP) sensor
• Common rail pressure sensor
• EGR valve position sensor
• Intake throttle position (ITP) sensor
• Fuel temperature (FT) sensor
• Vehicle speed (VS) sensor
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:
• EGR EVRV
• Intake throttle
• SCV
Terms Commonly Used in Diagnosis
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.
• EGR (exhaust gas recirculation)
Engine Control System 1A-41
• Engine speed
• Vehicle speed
• ECT (engine coolant temperature)
• IAT (intake air temperature)
• AP (accelerator position)
• FT (fuel temperature)
• Idle position switch
• Common rain pressure
Diagnostic Executive
The Diagnostic Executive is a unique segment of
software that 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 CHECK ENGINE lamp (MIL) on and
off
• DTC logging and clearing
• Tech 2 data recording
• Acquiring current status information on each
diagnostic
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 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 CHECK
ENGINE lamp (MIL) 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).
Basically, the MIL is turned on when the electronic
control system such as ECM (engine control module)
fails and a DTC is detected.
Data Link Connector (DLC)
The provision of communication with the control
module is the data link connector (DLC). The DLC is
used to connect to Tech 2, or a scan tool. Some
common uses of Tech 2 are listed below.
• Identifying stored diagnostic trouble codes (DTCs)
• Clearing DTCs
• Performing output control tests
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