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Cummins SPN 3364 FMI 2: Meaning, Causes & Fix

Aftertreatment 1 DEF Injector — data erratic, intermittent, or incorrect from DEF dosing injector

Reviewed by ASE Certified Mechanics · Last updated July 08, 2026

Quick Answer

SPN 3364 FMI 2 = DEF Injector Data Erratic
Severity: ⚠️ WARNING · System: DEF Injector · ✅ Can continue with caution

✅ {% if lang == "es" %}Revisado Editorialmente{% else %}Editorially Reviewed{% endif %} — {% if lang == "es" %}Última revisión{% else %}Last reviewed{% endif %} 2026-07-08 {% if lang == "es" %}por{% else %}by{% endif %} {% if lang == "es" %}analista de datos de flotas{% else %}fleet data analyst{% endif %}. {% if lang == "es" %}Esta definición de código ha sido verificada contra la documentación del estándar SAE J1939 y los manuales de servicio OEM para Cummins ISX15.{% else %}This code definition has been cross-referenced against SAE J1939 standard documentation and OEM service manuals for Cummins ISX15.{% endif %}

Diagnostic Reference

Field Details
Code SPN 3364 FMI 2
Protocol J1939 SPN: 3364 FMI: 2
Component DEF Injector
Manufacturer Cummins
Engine Series ISX15
Severity ⚠️ WARNING
SAE Reference SAE J1939-73 Digital Annex — SPN 3364, FMI 2

Possible Causes

  1. DEF injector internal failure
  2. Contaminated DEF causing deposits
  3. Wiring intermittent connection
  4. DEF crystal buildup on injector nozzle
  5. ECM software glitch

Diagnostic & Repair Procedure

  1. Step 1: Flush DEF system with certified DEF (32.5% urea)
  2. Step 2: Test DEF injector operation with INSITE diagnostic tool
  3. Step 3: Inspect wiring for intermittent connections or chafing
  4. Step 4: Clean or replace DEF injector if deposits or crystals found
  5. Step 5: Update ECM calibration if software update available

Frequently Asked Questions

Is this a false alarm or a real problem?

CHECK SOON codes are rarely false alarms. The ECM has detected a parameter outside normal operating range. Sensor malfunctions can sometimes trigger false readings, but the majority of CHECK SOON codes indicate a developing issue that will worsen if left unaddressed. Use a diagnostic scan tool to verify sensor readings before replacing expensive parts.

Can I diagnose this without a scan tool?

Basic visual inspection can be performed without a scan tool — check wiring harnesses for chafing, connectors for corrosion, and related components for physical damage. However, to verify the fault, view live sensor data, and confirm the repair, a heavy-duty diagnostic scan tool (or a compatible OBD-II adapter with J1939/J1708 support) is strongly recommended for accurate diagnosis.

How soon should I schedule service?

Schedule service within the next 1–3 operating days. While the vehicle can continue operating normally, delaying repair increases the risk of the fault escalating to CHECK NEXT STOP severity. Additionally, some CHECK SOON conditions are precursors to emissions system faults that will trigger a mandatory derate if not addressed in a timely manner.

Estimated Repair Cost

Typical repair: $100–800 (Parts: $50–500 + Labor: 1–3 hours) · Costs vary by make/model and location

Diesel Repair Cost & Downtime Estimator

Enter estimated labor hours to calculate repair cost and potential fleet downtime losses. Based on national average diesel shop rate of $150/hr and daily revenue loss of $800/day for a parked truck.

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SPN 639 FMI 9 🔴 STOP ENGINE
J1939 CAN Bus Communication Loss
SPN 1322 FMI 31 🟡 CHECK AT NEXT STOP
Misfire Detected on Cylinder 6
MID 128 SID 1 FMI 5 🟡 CHECK AT NEXT STOP
Injector Cylinder 1 Circuit

Associated Symptoms

Engine Derate Loss Of Power

References & Further Reading

Data Provenance: This fault code definition is derived from SAE J1939 standards. SPN 3364 FMI 2 is defined in SAE J1939-73 Digital Annex. Diagnostic procedures sourced from Cummins OEM technical service documentation. Not for safety-critical decisions. Consult a certified diesel mechanic before performing any repair. See our full disclaimer.