Navistar International DT 466 Diagnostic/Troubleshooting Manual page 48

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2. Signal conditioner
The signal conditioner in the internal microprocessor
converts analog signals to digital signals, squares up
sine wave signals, or amplifies low intensity signals to
a level that the ECM microprocessor can process.
3. Microprocessor
The ECM microprocessor
instructions (control strategies) and value tables
(calibration parameters). The ECM compares stored
instructions and values with conditioned input values
to determine the correct operating strategy for all
engine operations.
Continuous calculations in the ECM occur at
two different levels or speeds:
Background.
• Foreground calculations are much faster than
background calculations and are normally more
critical for engine operation. Engine speed control
is an example.
• Background calculations are normally variables
that change at slower rates. Engine temperature
is an example.
Diagnostic Trouble Codes (DTCs) are generated by
the microprocessor, if inputs or conditions do not
comply with expected values.
Diagnostic strategies are also programmed into the
ECM. Some strategies monitor inputs continuously
and command the necessary outputs to achieve the
correct performance of the engine.
Microprocessor Memory
The ECM microprocessor includes Read Only
Memory (ROM) and Random Access Memory (RAM).
ROM
ROM stores permanent information for calibration
tables and operating strategies. Permanently stored
information cannot be changed or lost by turning
the ignition switch to OFF or when ECM power is
interrupted. ROM includes the following:
• Vehicle configuration, modes of operation, and
options
• Engine Family Rating Code (EFRC)
• Engine warning and protection modes
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
1 ENGINE SYSTEMS
RAM
RAM stores temporary information for current engine
conditions.
when the ignition switch is turned to OFF or when
ECM power is interrupted. RAM information includes
the following:
•
stores operating
•
•
4. Actuator control
The ECM controls the actuators by applying a low
level signal (low side driver) or a high level signal (high
Foreground and side driver). When switched on, the drivers complete
a ground or power circuit to an actuator.
Actuators are controlled in three ways, determined by
the kind of actuator.
•
•
•
ECM Control of Engine Operation
The ECM controls engine operation with the following:
•
•
•
•
•
Variable Geometry Turbocharger (VGT) Control
Module
The VGT control module controls vane position in
the turbine housing. Vane position is controlled by
a switching voltage source in the ECM. The ground
circuit is supplied directly from the battery ground at
all times.
The actuator control is set by a pulse-width modulated
signal in response to engine speed, desired fuel
quantity, boost or exhaust back pressure and altitude.
EGES-270-1
Follow all warnings, cautions, and notes.
© August 2008 Navistar, Inc.
Temporary information in RAM is lost
Engine temperature
Engine rpm
Accelerator pedal position
A duty cycle (percent time on/off)
A controlled pulse-width
Switched on or off
Variable Geometry Turbocharger (VGT) control
module
EGR drive module and control valve
Diamond Logic® engine brake (brake shut-off
valve)
IPR valve
Inlet Air Heater (IAH) assembly