46 1 ENGINE SYSTEMS
The ECM uses CMP and CKP input signals to
calculate engine speed and position. The ECM
conditions both input signals and supplies the IDM
with CMP and CKP output signals. The IDM uses
CMP and CKP output signals to determine the correct
sequence for injector firing.
The ECM sends information (fuel volume, EOT, and
ICP) through the CAN 2 datalink to the IDM; the IDM
uses this information to calculate the injection cycle.
Injector Power Source
The IDM creates a constant 48 volt (DC) supply to
all injectors by making and breaking a 12 volt source
across a coil in the IDM. The 48 volts created by the
collapsed field is stored in capacitors until used by the
injectors.
The IDM controls when the injector is turned on and
how long the inje ctor is active . The IDM first energizes
the OPEN coil, then the CLOSE coil. The low side
driver supplies a return circuit to the IDM for each
injector coil (open and close). The high side driver
controls the power supply to the injector. During each
injection event, th e low and high side drivers a re
switched on and off for each coil.
IDM and Injector Diagnostics
The IDM determines if an injector is drawing enough
current. The IDM sends a fault to the ECM, indicating
potential problems in the wiring harness or injector,
and the ECM will set a DTC. The IDM also does
self-diagnostic checks and sets a DTC to indicate
failure of the IDM.
On demand tests can be done using the Electronic
Service Tool (EST). The EST sends a request to the
ECM and the ECM sends a request to the IDM to do
a test. Some tests generate a D TC when a problem
exists. O ther tests require the technician to evaluate
parameters, if a problem exists.
EGES-270-1
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
Follow all warnings, cautions, and notes.
© August 2008 Navistar, Inc.
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