SPN 651 FMI 5Fuel SystemHigh
Injector Cylinder 1 — Current Below Normal or Open Circuit
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Overview
Fault Code
SPN 651 / FMI 5
Category
Fuel System
Fault Type
electrical
FMI Category
current low
Severity
High
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: Cylinder 1 injector — front of engine on inline-6 configurations (passenger side front on V-configuration). Injector harness runs along valve cover rail to ECM. Connector typically located at top of valve cover near injector body.
Common Symptoms
- Cylinder 1 misfire — rough idle and uneven power delivery
- Engine knock or rattle from cylinder 1 at idle
- Black or white smoke from exhaust
- Reduced power and fuel economy
- Hard start or extended crank time
- MIL illuminated with active injector fault
Root Causes
- Injector solenoid open circuit — internal injector winding failure
- Broken or chafed injector harness wire — open circuit between ECM and injector
- Corroded or backed-out injector connector — high resistance causing low current
- ECM injector driver circuit failure — internal ECM fault (less common)
- Injector return circuit open — missing ground path
- Injector body failure — mechanical seizure causing electrical open
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Derate Behavior
Power Derate
Yes
Mileage / Regen Notes
Injector solenoid winding failure increases significantly above 400,000 miles. Harness chafing risk increases with age and heat cycling.
System Interactions
SPN 651 FMI 5 interacts with the following systems and may trigger cascading faults if not resolved promptly.
Fuel rail pressure — injector timing and quantity affected
Engine power output — derate may be triggered to protect injectors
Aftertreatment regen — low fuel pressure can prevent regen completion
TSB Reference: Cummins TSB 4021756 — Injector Solenoid Circuit Diagnosis; Detroit TSB 16-008 — Injector Open Circuit Diagnosis; PACCAR TSB FU-003 — Injector Electrical Fault Diagnosis
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.
Replacing injectors without verifying fuel supply pressure — low supply pressure causes injector faults.
Ignoring fuel filter restriction — a clogged filter causes low rail pressure that mimics injector failure.
OEM Notes
Cummins
ISX/X15: Injector harness chafing against valve cover is common. Inspect harness routing at valve cover rail. INSITE injector test required to confirm cylinder contribution after repair.
Detroit
DD15/DD13: Injector connector corrosion at cylinder 1 is common on high-mileage engines. Clean connector with electrical contact cleaner before replacing injector. DDDL cylinder cutout test required.
PACCAR
MX-13: Injector solenoid failure on high-mileage MX-13 is common. Confirm with DAVIE4 injector test before removal. Check for companion SPN 157 (fuel rail pressure) faults.
Volvo
MP8: Injector harness routing near turbo outlet is a known chafe point. Inspect harness at turbo area. PTT injector contribution test required.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 651 FMI 5 — 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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