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 Cummins X12 dosing injector injects DEF into the exhaust to feed the SCR catalyst. FMI 5 means the electrical circuit for the injector is open — the ACM is sending a command but no current is flowing. Without DEF injection, NOx conversion stops and the inducement sequence will begin. The fault is almost always a wiring problem or a failed injector coil, both of which are repaired or replaced at the injector or its harness rather than requiring replacement of the entire aftertreatment system.
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 X12 engines, the ACM monitors injector circuit current during activation events. When the ACM commands activation and detects no current, FMI 5 is logged. INSITE supports injector actuation tests and can confirm whether the open circuit is in the wiring, the connector, or the injector coil itself.
Common Symptoms
- SCR efficiency or NOx conversion fault active alongside SPN 3480 FMI 5
- DEF dosing quantity at zero or below commanded levels in INSITE
- DEF system warning lamp on the instrument panel
- SCR inducement sequence may begin if DEF dosing is absent for extended operation
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Open circuit in the DEF injector wiring harness
- Corroded or disconnected injector connector
- Failed DEF dosing injector solenoid coil
- ACM output circuit fault (uncommon)
First Checks
- Connect Cummins INSITE and run the dosing injector actuation test to confirm the circuit is not responding
- Inspect the injector wiring harness and connector for damage or corrosion
- Measure injector coil resistance — an open reading confirms a failed solenoid
- Trace the harness back to the ACM connector if resistance and connector appear normal
- Replace the injector if coil failure is confirmed
Can I Keep Driving?
The X12 is driveable with this fault active, but the SCR system cannot function without DEF dosing. The inducement sequence will progress. Repair the injector circuit fault promptly to prevent inducement escalation.
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
Is the DEF dosing injector on the Cummins X12 interchangeable with the ISX15?
The Cummins X12 and ISX15 may share some aftertreatment components depending on the production configuration, but the dosing injector part number should be confirmed by engine serial number before ordering. Using an incorrect injector can produce flow or pressure issues that cause different fault codes. Cummins QuickServe Online provides part number lookup by serial number.
Can moisture in the DEF injector connector cause SPN 3480 FMI 5 on the X12?
Yes. Moisture and road splash can enter the injector connector over time, particularly on connectors located in exposed areas of the exhaust system. Corrosion on the connector pins can increase resistance to the point of appearing as an open circuit to the ACM. Cleaning and dielectric-greasing the connector, or replacing a severely corroded connector, can resolve the fault when the injector coil itself tests within specification.
Will SPN 3480 FMI 5 on the X12 cause the catalyst to be damaged from excess NOx?
The SCR catalyst itself is not damaged by operating without DEF dosing — it simply has no reagent to reduce NOx, so NOx passes through unconverted. The catalyst will resume normal function once DEF dosing is restored. The inducement sequence will escalate if dosing remains absent, but the catalyst does not require replacement or special regeneration after a DEF dosing circuit fault is repaired.