Code Details
| Display code | SPN 3480 FMI 5 |
|---|---|
| SPN | 3480 |
| FMI | 5 |
| OEM code | None listed |
| Manufacturer | PACCAR |
| 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 PACCAR MX-13 DEF dosing injector sprays DEF into the exhaust for SCR NOx reduction. When the control circuit has an open fault, the actuator cannot open the injector valve �?DEF delivery stops, the SCR catalyst has no reagent, and the efficiency fault and inducement sequence follow. On Kenworth and Peterbilt trucks with the MX-13, the diesel exhaust brake uses back-pressure control via the VGT to create engine braking without traditional engine brake hardware. DAVIE4 and PACCAR ESA display exhaust brake enable status, VGT position, and exhaust back-pressure in real time. SPN 3480 FMI 5 indicates an open circuit in the exhaust brake actuator electrical circuit, which is separate from the VGT actuator used for engine power management. Check the exhaust brake actuator connector and wiring before assuming actuator failure.
SPN 3480 FMI 5 is DEF Dosing Unit control circuit current below normal or open. On the PACCAR MX-13 aftertreatment system, DAVIE provides live DEF dosing quantity and can command a dosing test cycle. Zero dosing quantity combined with FMI 5 confirms the injector circuit is open. Measuring coil resistance at the connector distinguishes a wiring fault from a failed injector.
Common Symptoms
- SPN 5246 FMI 31 (SCR efficiency) active alongside this fault
- DEF dosing quantity showing zero in PACCAR DAVIE
- SCR inducement warning on the Kenworth or Peterbilt instrument cluster
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Damaged or chafed wire in the DEF dosing injector harness
- Corroded injector connector
- Failed dosing injector with an open coil
First Checks
- Connect PACCAR DAVIE and check active codes alongside SPN 3480 FMI 5
- Inspect the dosing injector harness and connector for physical damage
- Measure injector coil resistance �?open (infinite ohms) confirms a failed coil
- If wiring checks out, replace the dosing injector
- Inspect the exhaust brake actuator connector and wiring harness for corrosion or damage
- Check exhaust brake actuator resistance with a multimeter and compare to specification
Can I Keep Driving?
Driveable, but the SCR system is not converting NOx and the inducement sequence will escalate to a derate if the fault is not repaired.
Related Codes
Related Lookup Pages
Sources
- PACCAR / Kenworth / Peterbilt Service Support — MX Engine Resources PACCAR Inc. · oem · accessed 2026-06-11 · confidence medium
Source: PACCAR Inc., PACCAR / Kenworth / Peterbilt Service Support — MX Engine Resources. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - PACCAR Engine Technical Services PACCAR Inc. · oem · accessed 2026-06-10 · confidence medium
Source: PACCAR Inc., PACCAR Engine Technical Services. 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 PACCAR MX-13 the same part as on the MX-11?
The MX-13 and MX-11 use similar aftertreatment architecture with comparable dosing injector designs. Part numbers may differ between the two engines due to different aftertreatment sizing. DAVIE part look-up or the PACCAR parts portal can confirm the correct injector for the specific engine.
Can urea crystallization at the dosing injector tip cause SPN 3480 FMI 5 on the MX-13?
Urea crystallization at the injector tip can cause flow restriction (typically FMI 7 or FMI 0 type faults from inadequate dosing flow) but does not cause an open circuit fault (FMI 5). FMI 5 is strictly an electrical open �?the solenoid coil is not conducting. Deposit buildup and coil failure are separate failure modes.
Does PACCAR DAVIE allow a DEF dosing injector test on the MX-13?
Yes. DAVIE includes a DEF system diagnostic function that can command a dosing test cycle and monitor the dosing quantity response. This confirms whether the injector is responding to commands. An injector that commands but shows zero flow has a mechanical blockage; one that does not respond at all has a circuit fault consistent with FMI 5.