7 ELECTRONIC CONTROL SYSTEMS DIAGNOSTICS 445
IAH Circuit Operation
Figure 454 IAH circuit diagram
The IAH control system operation is dependent upon
the ECT, EOT, BAP, and battery voltage. The IAH
relays are activated by power supplied by the ECM
through Pin X1–17 to circuit 97CH. The IAH relays are
grounded through circuit 97APG3, Pin 4 on the 12-pin
connector, and to negative battery terminal. Power is
supplied to the switch side of the IAH relays from the
starter motor. When the IAH relay is energized, power
is supplied to the IAH elements that are grounded
through the intake manifold.
The WAIT TO START la mp time is transmitted over the
CAN 1 datalink. See truck Chassis Electrical Circuit
Diagram Manual .
Fault Detection / Management
An open or short to ground in the IAH control circuit
can be detected by doing an on-demand Output
Circuit Check (OCC) during the KOEO Standard Test.
When a fault is detected, a DTC will be set.
IAH Diagnostic Trouble Codes (DTCs)
DTC 251
IAH OCC self-test failed
• DTC 251 is set by the ECM when the OCC test
has failed after the KOEO Standard Test has been
run.
• DTC 251 can be set when a poor connection, an
open or short to ground in the relay control circuit,
or failed relay exists.
NOTE: For initial calibrations:
• If the system voltage is less than 13 volts, DTC
251 may become active.
• If the system is functioning properly, disregard
DTC 251.
Later calibrations and current hardware levels do not
support DTC 251.
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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