SPN 1326 FMI 13Engine Protection
Misfire Cylinder 4 - Out of Calibration
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Overview
Fault Code
SPN 1326 / FMI 13
Category
Engine Protection
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: Cylinder 4 combustion chamber, fuel injector, and associated sensors are located on the engine block fourth cylinder position.
Common Symptoms
- Rough idle or engine vibration
- Reduced engine power and acceleration
- Increased exhaust smoke, white or black
- Higher fuel consumption
- Engine runs rough under load
- Check engine light illuminated
Root Causes
- Injector calibration code (IQA/IQAN trim code) not programmed or incorrectly entered into ECM for cylinder 4
- Replacement injector installed without updating trim code in ECM
- Corrupted or lost injector calibration data in ECM memory
- Worn or degraded injector in cylinder 4 causing fueling deviation beyond calibration range
- ECM software issue or failed ECM not retaining injector trim codes
- Incorrect injector part number installed in cylinder 4
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Derate Behavior
Power Derate
Yes
Mileage / Regen Notes
Active and parked DPF regeneration will be inhibited or severely limited while a cylinder misfire fault is active, as unburned fuel risk to the aftertreatment system triggers regen lockout. Fault must be resolved and cleared before normal regen resumes.
System Interactions
SPN 1326 FMI 13 interacts with the following systems and may trigger cascading faults if not resolved promptly.
ECM communication — J1939 network faults can affect all connected modules
Engine protection — ECM may trigger derate to prevent damage
Aftertreatment — engine protection derates can affect regen strategy
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 1326 FMI 13 — 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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