Code Details
| Display code | SPN 3480 FMI 5 |
|---|---|
| SPN | 3480 |
| FMI | 5 |
| OEM code | None listed |
| Manufacturer | Detroit Diesel |
| 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 on the DD15 injects DEF into the exhaust stream to enable NOx reduction in the SCR catalyst. An open circuit fault means the control system detects no current path through the injector �?DEF delivery stops, SCR efficiency drops, and the inducement sequence will begin if the fault persists. On Freightliner Cascadia and Western Star trucks with the DD15, the exhaust brake (Jake brake equivalent using back-pressure control via VGT) shares actuator wiring with the VGT system. DiagnosticLink can command the exhaust brake actuator and monitor its position response. SPN 3480 FMI 5 indicates an open circuit in the actuator electrical path. On high-mileage Cascadia trucks, the exhaust brake actuator connector can develop fretting corrosion at the connector terminals from the vibration environment near the exhaust system. Cleaning and re-seating the connector is the first recommended step before actuator replacement.
SPN 3480 relates to the Aftertreatment DEF Dosing Unit in J1939. FMI 5 indicates current below normal or open circuit in the injector driver circuit. On Detroit DD15 with ACM2.0, DiagnosticLink can command the dosing injector to test circuit response and displays actual DEF dosing quantity in live data. An injector that commands successfully but flows no DEF has a mechanical fault; one that does not respond at all has a circuit fault.
Common Symptoms
- SPN 5246 FMI 31 (SCR efficiency) active alongside this code
- DEF dosing quantity reading zero in DiagnosticLink
- SCR inducement countdown starting if fault persists
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Broken or chafed wire in the DEF dosing injector harness
- Corroded or damaged injector connector
- Failed DEF dosing injector with open coil
- ACM driver fault in rare cases
First Checks
- Connect DiagnosticLink and check active codes �?SPN 5246 FMI 31 alongside this confirms no DEF is reaching the catalyst
- Inspect the DEF dosing injector harness and connector for visible damage or corrosion
- Measure injector coil resistance at the connector with a multimeter �?an open reading (infinite resistance) confirms a failed injector coil
- If wiring and coil are serviceable, investigate the ACM driver circuit
- Inspect and clean the exhaust brake actuator connector at the actuator body — check for fretting corrosion on the terminal pins
- Measure the exhaust brake actuator resistance at the connector with a multimeter and compare to specification
Can I Keep Driving?
The truck remains driveable but the SCR system is not converting NOx. The inducement sequence will escalate to a derate if the fault is not repaired.
Related Codes
Related Lookup Pages
Sources
- Detroit Diesel Service and Diagnostic Resources — Public Reference Detroit Diesel (Daimler Truck North America) · oem · accessed 2026-06-11 · confidence medium
Source: Detroit Diesel (Daimler Truck North America), Detroit Diesel Service and Diagnostic Resources — Public Reference. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - DiagnosticLink Detroit Diesel Corporation · oem · accessed 2026-05-05 · confidence medium
Source: Detroit Diesel Corporation, DiagnosticLink. 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
Can the DEF dosing injector on the Detroit DD15 be cleaned to restore operation after SPN 3480 FMI 5?
FMI 5 is an open circuit fault �?the solenoid coil is not conducting. Cleaning cannot fix a failed coil. If the coil resistance measures open (infinite ohms), the injector must be replaced. Cleaning the injector tip is appropriate for FMI 7 (mechanical fault) or flow restriction faults, not for electrical open circuit faults.
How do I access the DEF dosing injector on a Freightliner Cascadia with a DD15?
The DEF dosing injector on the DD15 is located in the aftertreatment system's exhaust pipe, upstream of the SCR catalyst. In a Freightliner Cascadia, the aftertreatment system is typically mounted under the cab or along the frame rail. Access varies by configuration, but the injector tip is threaded into the exhaust pipe and the electrical connector is nearby. DiagnosticLink's wiring diagram function can identify the exact harness routing for the specific chassis.
Will a new DEF dosing injector need calibration on the DD15 after replacement?
The DEF dosing injector on the DD15 does not require individual calibration coding in the same way fuel injectors do. After replacement, DiagnosticLink can run the aftertreatment system resets and confirm the new injector is responding to dosing commands. A drive cycle to verify SCR efficiency returns to normal is recommended after replacement.