374 7 ELECTRONIC CONTROL SYSTEMS DIAGNOSTICS
ECM / IDM Circuit Op e r at ion
Figure 422 ECM / IDM circuit diagram
The ECM / IDM communication link consists of a
series of interdependent signals that include the
CKPO, CMPO, and the CAN 2 datalink.
The CKPO signal is a 0 V to 12 V signal that
communicates (from ECM to IDM) the position of
the cranksh aft. The signal is used by the IDM
to synchronize the injector firing sequence and
is calculated from the signal generated from the
CKP sensor. The ECM generates the CKPO
signal by pullin g down (switc hing to ground) a 12
V communication circuit in the IDM.
The CMPO signal is a 0 V to 12 V signal that
communicates (from ECM to IDM) the position
of the camshaft. The signal is used by the IDM
to synchronize the injector firing sequence and
is calculated from the signal generated from the
CMP sensor. The ECM generates the C MPO
signal by pullin g down (switc hing to ground) a 12
V communication circuit in the IDM.
CAN 2 datalink is a J1939 high speed private
communication datalink between the ECM, IDM, and
EGR drive module. The ECM receives messages
that include injector coil status, IDM calibratio n leve l,
CMPO and CKPO DTCs, injector DTCs, IDM DTCs,
and injector test results from the IDM. The IDM
receives injector diagnostic commands, operation
strategies, modes and conditions from the E CM.
NOTE: CAN 2 datalink is used only as communication
between the ECM, IDM, and EGR drive m o dule.
There is no relation to the CAN 1 datalink that is
used for communication with various processors on
a vehicle.
Fault Detection / Management
The ECM continuously monitors the IDM. When
the ECM fails to receive required continuous
communication from the IDM, the ECM will set a
DTC.
ECM / IDM Diagnostic Trouble Codes (DTCs)
DTCs are read using the Electronic Service Tool (EST)
or by counting the flashes from the amber and red
ENGINE lamp.
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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