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 lamp 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.

• EST with MasterDiagnostics® software
• EZ-Tech® interface cable
• Digital Multimeter (DMM)

• 12-pin Breakout Harness
• Breakout Box
• Amp Clamp