Code Details
| Display code | SPN 3480 FMI 5 |
|---|---|
| SPN | 3480 |
| FMI | 5 |
| OEM code | None listed |
| Manufacturer | Cummins |
| System | Aftertreatment — DEF dosing system |
| Component | DEF dosing injector / wiring circuit |
| Source address | Unknown or not applicable |
| Severity | medium |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-12 |
Plain-English Meaning
The ISB 6.7 DEF dosing injector injects DEF into the exhaust ahead of the SCR catalyst. FMI 5 means the control circuit is open — the ACM commands the injector but no current flows. Without DEF dosing, the SCR catalyst loses its reductant source and NOx conversion stops. The fault is almost always a wiring or connector issue or a failed injector solenoid. INSITE can confirm the circuit status and guide the repair.
SPN 3480 is related to Aftertreatment DEF Dosing Unit control in J1939. FMI 5 indicates current below normal or open circuit in the injector control path. On Cummins CM2350 ISB 6.7 engines, the ACM drives the dosing injector solenoid. When the ACM commands activation and detects no current feedback, FMI 5 is set. INSITE's injector actuation test commands the injector while monitoring circuit response, making it the primary tool for distinguishing a wiring fault from an injector coil failure.
Common Symptoms
- SCR efficiency or NOx conversion fault alongside SPN 3480 FMI 5
- DEF dosing quantity at zero or below commanded levels in INSITE
- DEF or aftertreatment warning lamp on the instrument panel
- SCR inducement may begin if the injector remains inoperative
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Broken wire in the DEF injector harness
- Corroded or disconnected injector electrical connector
- Failed DEF dosing injector solenoid coil
- ACM output circuit fault (less common)
First Checks
- Connect Cummins INSITE and run the injector actuation test to confirm circuit response
- Inspect the injector harness and connector for damage, corrosion, or moisture intrusion
- Measure injector coil resistance at the connector — an open reading confirms a failed coil
- If coil resistance is normal, trace the harness to the ACM connector for open circuits or high-resistance splices
- Replace the injector if coil resistance confirms an open internal solenoid
Can I Keep Driving?
Without DEF dosing, the SCR catalyst does not receive reductant and NOx conversion stops. An SCR efficiency fault will set and the inducement sequence will begin. The truck is driveable but the injector circuit fault must be corrected before the inducement advances to a significant derate.
Related Codes
Related Lookup Pages
Sources
- Cummins INSITE Service Tool — Public Reference Documentation Cummins Inc. · oem · accessed 2026-06-11 · confidence medium
Source: Cummins Inc., Cummins INSITE Service Tool — Public Reference Documentation. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - QuickServe Online Cummins Inc. · oem · accessed 2026-05-05 · confidence medium
Source: Cummins Inc., QuickServe Online. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - SAE J1939 Standards Collection SAE International · official · accessed 2026-05-05 · confidence medium
Source: SAE International, SAE J1939 Standards Collection. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
How is the DEF dosing injector accessed on an ISB 6.7 installation?
The DEF dosing injector on the ISB 6.7 is threaded into the exhaust pipe upstream of the SCR catalyst. Access varies by vehicle chassis and exhaust routing. In many medium-duty truck and bus applications, the aftertreatment system is located under the vehicle frame, and the injector is reachable without major disassembly. Always allow the exhaust system to cool before handling injector components.
Can the ISB 6.7 DEF dosing injector become stuck in the exhaust pipe after high-mileage operation?
Yes. Urea deposits and heat cycles can cause the injector thread to seize in the exhaust bung over time. Applying penetrating oil and allowing adequate soak time before attempting removal is recommended. If the injector is stuck, a special injector removal tool may be needed to avoid damaging the exhaust bung or the injector tip.
Does replacing the DEF dosing injector on the ISB 6.7 require an INSITE calibration?
Typically, replacing the DEF dosing injector does not require a special INSITE calibration specific to the injector itself, as the injector does not carry unique calibration data like a fuel injector might on some platforms. However, any active fault codes should be cleared after replacement and a drive cycle completed to verify the circuit fault does not return. INSITE should be used to confirm the dosing quantity is within the commanded range after the repair.