SPN 3361 — Aftertreatment 1 DEF Dosing Unit
System: Aftertreatment / DEF
The DEF doser (injector) that sprays diesel exhaust fluid into the exhaust ahead of the SCR catalyst.
Can I keep running it?
HIGH — limit use, diagnose now
A doser that is stuck, clogged or not firing means NOx is not being reduced, and inducement derates will follow. Repair soon.
Likely causes
- White urea crystals blocking the doser tip or mixer
- Doser coil open or shorted
- DEF wicked into the doser connector or harness
- Doser stuck open and dribbling after shutdown
Checks & fixes (easiest first)
- Pull the doser and inspect the tip and mixer pipe for crystal buildup
- Run the OEM dosing quantity (cup) test and compare with spec
- Measure coil resistance and inspect the connector for DEF intrusion
- Soak light deposits off in warm water; replace the doser if spray or volume stays wrong
Common FMIs with SPN 3361
- SPN 3361 FMI 3Voltage above normal or shorted high
- SPN 3361 FMI 4Voltage below normal or shorted low
- SPN 3361 FMI 5Current below normal or open circuit
- SPN 3361 FMI 6Current above normal or grounded circuit
- SPN 3361 FMI 7Mechanical system not responding or out of adjustment
Related codes
- SPN 4334Aftertreatment 1 DEF Doser Absolute Pressure
- SPN 4364Aftertreatment 1 SCR Conversion Efficiency
- SPN 5246Aftertreatment SCR Operator Inducement Severity
Troubleshooting guides
FAQ
What does SPN 3361 mean?
SPN 3361 is Aftertreatment 1 DEF Dosing Unit. The DEF doser (injector) that sprays diesel exhaust fluid into the exhaust ahead of the SCR catalyst.
Can I keep running with SPN 3361?
A doser that is stuck, clogged or not firing means NOx is not being reduced, and inducement derates will follow. Repair soon.
What causes SPN 3361?
White urea crystals blocking the doser tip or mixer; Doser coil open or shorted; DEF wicked into the doser connector or harness; Doser stuck open and dribbling after shutdown.