SPN 1233 FMI 0Fuel
Fuel Pump Secondary Circuit Intermittent
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 1233 / FMI 0
Category
Fuel
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: Secondary fuel pump is typically mounted on the fuel tank assembly or along the frame rail in the fuel supply line.
Common Symptoms
- Engine stalling or sudden shutdown
- Hard starting or extended cranking
- Rough running or hesitation under load
- Intermittent loss of power
- Engine may restart after sitting
Root Causes
- Intermittent open or short in fuel pump wiring harness Faulty fuel pump relay or connector Corroded or loose electrical connections at fuel pump Failing fuel pump with intermittent internal electrical fault Damaged or chafed wiring near fuel tank or frame rail
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Derate Behavior
Power Derate
No
System Interactions
SPN 1233 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.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 1233 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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