SPN 728 FMI 0Transmission
Transmission Control System MIL Request Circuit/Open
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 728 / FMI 0
Category
Transmission
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: The transmission control module is typically mounted on or near the transmission case, with MIL request circuit wiring routed to the engine control module.
Common Symptoms
- Malfunction indicator lamp illuminated on instrument cluster
- Transmission fault code active with no other transmission symptoms
- Check engine light on with no performance issues
- Communication warning between ECM and TCM
Root Causes
- Open circuit in MIL request signal wire between TCM and ECM Faulty transmission control module Damaged wiring harness or connector between TCM and ECM ECM not receiving MIL request signal from TCM Corroded or loose connector pins in datalink circuit
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Derate Behavior
Power Derate
No
System Interactions
SPN 728 FMI 0 interacts with the following systems and may trigger cascading faults if not resolved promptly.
Common Diagnostic Mistakes
Replacing the sensor without verifying wiring continuity and supply voltage first.
Clearing codes without identifying and resolving the root cause — the fault will return.
Ignoring related active faults — cascading faults often share a root cause.
Skipping the connector inspection — corrosion and damaged pins are a leading cause of sensor faults.
Condemning the ECM before exhausting all wiring and component tests.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 728 FMI 0 — Full FSM Sequence & Repair Steps — includes wiring notes, sensor specs, and gated repair procedures.
Authority References
Diagnostic procedures on this page are informed by OEM service literature and industry standards.
Cummins QuickServe OnlineOfficial Cummins service manuals, fault code lookup, and TSB database.Detroit Diesel DiagnoCentralDetroit Diesel diagnostic procedures, DDDL documentation, and service literature.PACCAR MX Engine ServicePACCAR MX-11 and MX-13 engine service documentation and DAVIE diagnostic guides.Volvo/Mack Tech ToolVolvo and Mack engine fault code reference and PTT/Tech Tool diagnostic procedures.ASE — Diesel Truck Technician CertificationNational Institute for Automotive Service Excellence — T2 Diesel Engines certification standards.EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx standards.
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