SPN 729 MFI [3,4,5] Explained, Troubeshooting

SPN 729 is a diagnostic trouble code for Engine Intake Air Heater Driver #1.

FMI 3 – Voltage Above Normal, Or Shorted To High Source
FMI 4 – Voltage Below Normal, Or Shorted To Low Source
FMI 5 -Current Below Normal Or Open Circuit

ECM calibration, intake air heater relay