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Fault Code Reference

SPN 1323 FMI 13Engine Protection

Misfire Cylinder 1 - Out of Calibration

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Overview

Fault Code

SPN 1323 / FMI 13

Category

Engine Protection

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

No

Component Location: Cylinder 1 injector is located on the engine's cylinder head at the first cylinder position, typically at the front of the engine on inline configurations.

Common Symptoms

  • Rough idle
  • Loss of power
  • Increased exhaust smoke
  • Engine misfire detected on cylinder 1
  • Check engine light illuminated
  • Decreased fuel economy
  • Engine vibration

Root Causes

  • Injector calibration code (IQA/trim code) not programmed or incorrectly entered into ECM after injector replacement
  • Faulty or worn fuel injector on cylinder 1 causing inconsistent fuel delivery
  • Low compression on cylinder 1 due to worn rings, valve seating issues, or head gasket leak
  • Incorrect injector installed (wrong part number) on cylinder 1
  • ECM software not updated after injector replacement or ECM replacement
  • Injector return/leak-off excessive on cylinder 1 causing fuel delivery variance
  • Air in fuel system affecting cylinder 1 injection timing and quantity
  • Camshaft or crankshaft position sensor signal quality issue causing misfiring detection error

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Derate Behavior

Power Derate

Yes

Mileage / Regen Notes

Active and parked DPF regeneration will be inhibited or suspended when a misfire fault is active on cylinder 1, as unburned fuel entering the aftertreatment system poses a risk of DPF damage or thermal runaway. Regen will remain inhibited until the misfire fault is resolved and cleared.

System Interactions

SPN 1323 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.

Deep-dive diagnostic page: SPN 1323 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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