7 ELECTRONIC CONTROL SYSTEMS DIAGNOSTICS 483
12–Pin Breakout Harness
Figure 475 IDM PWR circuit diagram
CAUTION: To avoid engine damage, turn the ignition switch to OFF before removing IDM relay or
disconnecting any connectors supplying power to the IDM. Failure to turn the ignition switch to OFF will
cause a voltage spike and damage to electrical components.
Voltage Checks at 12-pin Connector – Key-On Engine-Off (Check with breakout harness connected to
engine harness and chassis harness at 12–pin connector, IDM relay installed, and key-on engine-off. Follow
tests in order. Inspect for bent pins or corrosion.)
Test Point
Spec Comment
9 to gnd 12 V ±1.5 V
Power from ignition switch to IDM. If no voltage, see truck Chassis Electrical
Circuit Diagram Manual for circuit numbers, connector and fuse locations.
8 to gnd 0.06 V to 2
V
IDM MPR – 12–pin connector. If > 2 V, check for open circuit between IDM
Pin X3–27 to Pin 8.
12 to gnd 12 V ±1.5 V
IDM power from re lay Pin 87. If no voltage, check from Pin 12 to Pin 87
on relay for open or short to ground.
6 to gnd 12 V ±1.5 V
IDM logic power from relay Pin 87 with fuse. If fuse is blown, check for
short to ground. If fuse is good, check for open circuit between fuse to Pin
6. See truck Chas sis Electrical Circ uit Diagram Manual fo r circuit nu mbers,
connector and fuse locations.
1tognd 0Vto0.25
V
Ground – voltage reading indicates poor ground to battery. If voltage is
present check for open or high resistance between battery (–) and IDM pins.
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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