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 | 2026-06-11 |
Plain-English Meaning
The DEF dosing injector sprays a precise amount of DEF into the exhaust stream upstream of the SCR catalyst. Without a working injector, no DEF reaches the catalyst, NOx conversion stops, and the SCR efficiency code will set. FMI 5 means the ECM is detecting that the circuit is open �?no current is flowing through the injector, which is needed to open the valve and spray DEF.
SPN 3480 is related to the Aftertreatment DEF Dosing Unit control. FMI 5 indicates current below normal or open circuit in the injector control circuit. On Cummins CM2350 ISX15/X15, the aftertreatment control module (ACM) drives the dosing injector solenoid. An open circuit can result from a broken wire, a failed injector coil, or a connector fault. Cummins Insite can command the dosing injector to confirm whether the circuit responds.
Common Symptoms
- SCR efficiency fault (SPN 5246 FMI 31) active alongside this code
- DEF dosing injector not spraying �?visible in Insite DEF dosing quantity data
- Possible SCR inducement starting if the fault persists
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Broken wire in the DEF dosing injector harness
- Corroded or disconnected injector connector
- Failed DEF dosing injector coil (open coil resistance)
- ACM control driver fault in rare cases
First Checks
- Connect Cummins Insite and check active codes �?SPN 5246 FMI 31 alongside this fault confirms DEF is not reaching the catalyst
- Inspect the DEF dosing injector harness and connector for physical damage or corrosion
- Measure injector coil resistance with a multimeter at the injector connector �?should be within the spec for the injector type (typically 1 to 10 ohms depending on design; an open reading of infinite resistance confirms a failed coil)
- If wiring and connector are intact and the coil measures open, replace the DEF dosing injector
Can I Keep Driving?
Without DEF dosing, the SCR system cannot convert NOx. The SCR efficiency fault will set, and the inducement sequence will begin. The truck is still driveable, but the fault must be repaired before the inducement derate escalates.
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 do I access the DEF dosing injector on a Cummins ISX15 or X15 for replacement?
The DEF dosing injector on the ISX15 and X15 is located in the aftertreatment system, typically upstream of the SCR catalyst in the exhaust pipe. Access varies by truck chassis, but the injector is usually reachable without major disassembly. The injector tip is threaded into the exhaust pipe and sealed with a heat-resistant seal. Cummins recommends using fresh thread sealant and torquing to spec when reinstalling.
Can the DEF dosing injector tip on the ISX15 be cleaned rather than replaced?
A DEF dosing injector with crystallized urea deposits at the tip can sometimes be cleaned to restore flow. However, FMI 5 indicates an open circuit fault in the solenoid coil �?this is not a deposit or flow issue. An injector with a confirmed open coil must be replaced.
Will a failed DEF dosing injector cause the SCR catalyst to be damaged on the ISX15?
Not in the short term. Without DEF dosing, the SCR catalyst simply has no reagent to react with and NOx passes through unconverted. The catalyst is not damaged by operating without DEF dosing. However, the SCR efficiency fault will trigger the inducement sequence, and prolonged operation without DEF delivery will result in a progressive derate.