7 ELECTRONIC CONTROL SYSTEMS DIAGNOSTICS 489
INJ Circuits (Injector Drive)
Figure 476 Function diagram for the INJ circuit
The function diagram for INJ circuit includes the
following:
• Injectors
• Electronic Control Module (ECM)
• Injector Driver Module (IDM)
• Controller Area Network (CAN 1) link
• Camshaft Position Output (CMPO) signal
• Crankshaft Position Output (CKPO) signal
Function
The IDM is used to control the injectors. The IDM
receives CMPO and CKPO signals and fueling
information via CAN from the ECM. The IDM
calculates injection timing and injector actuation
time based on the fuel quantity requested for any
engine operation condition.
INJ Circuit Operation
When a coil needs to be energized the IDM turns on
both th e high a nd low side driver.
High Side Drive Output
The IDM regulates the current at an average of 20 A.
When the current reaches 24 A the IDM shuts off the
high side driver. When the current drops to 16 A the
IDM turns on the high side driver.
Low Side Drive Return
The injector solenoids are grounded through the low
side return circuits. The ECM monitors the low side
return circ uits. T he ECM monitors the lo w side return
signal for diagnos tic pu rp oses and utilizes th e fly-back
current from the injector solenoids to help charge the
drive c apacitors internal to the ECM.
Fault Detection / Management
When the engine is running, the IDM can detect
individual injector coil open and shorts to ground or
battery. A KOEO Injector Test allows the operator
to enable all injector coils when the engine is off to
verify circuit operation. When the IDM detects a fault,
Diagnostic Trouble Codes (DTCs) are transmitted
overtheCAN2linebetweentheECMandIDM.
The IDM transmits a high and low side drive output
to the injectors. The high side output supplies the
injectors with a power supply of 48 V DC at 20 A. The
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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