SPN 652 FMI 7Fuel SystemHigh
Injector Cylinder 2 - Mechanical System Not Responding
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Overview
Fault Code
SPN 652 / FMI 7
Category
Fuel System
Severity
High
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: Cylinder 2 injector is mounted in the cylinder head at the second cylinder position, accessed from the top of the engine under the valve cover.
Common Symptoms
- Rough engine idle or misfire on cylinder 2
- Loss of power or reduced engine performance
- Excessive smoke from exhaust (black or white)
- Engine noise or knock from cylinder 2
- Poor fuel economy
- Hard start or extended crank time
- Active or pending misfire codes alongside SPN 652 FMI 7
Root Causes
- Sticking or mechanically failed injector on cylinder 2 (needle seizure or stuck open/closed)
- Internal injector wear causing incorrect metering response
- Contaminated fuel causing injector fouling or debris blockage
- Low fuel supply pressure causing injector mechanical failure to respond
- Worn or damaged injector return check valve
- High-pressure fuel pump wear reducing rail pressure to injector
- Air in fuel system causing injector cavitation
- Injector hold-down clamp loose or improper installation affecting spray pattern
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Derate Behavior
Power Derate
Yes
Mileage / Regen Notes
Active and passive DPF regeneration may be inhibited due to cylinder 2 misfire or abnormal combustion; unburned fuel or raw hydrocarbons entering exhaust can damage DPF catalyst if injector is stuck open.
System Interactions
SPN 652 FMI 7 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: Injector TSBs
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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 652 FMI 7 — 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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