Home › Codes › SPN 3361 › FMI 5

SPN 3361 FMI 5

Aftertreatment 1 DEF Dosing Unit — Current below normal or open circuit.
Less current is flowing in an output or sensor circuit than expected, which usually means the circuit is open.

What the SPN covers: The DEF doser (injector) that sprays diesel exhaust fluid into the exhaust ahead of the SCR catalyst. More on SPN 3361.

What FMI 5 usually points to: Broken wire, unplugged connector, burned-out coil or solenoid, or a backed-out terminal. More on FMI 5.

Severity

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

  1. Wiring or connector fault in this circuit (most common for electrical FMIs)
  2. White urea crystals blocking the doser tip or mixer
  3. Doser coil open or shorted
  4. DEF wicked into the doser connector or harness
  5. Doser stuck open and dribbling after shutdown

Checks & fixes (easiest first)

  1. Inspect the connector and harness for this circuit: corrosion, water, chafing, backed-out pins
  2. Check the reference voltage, ground and signal at the component per OEM pin-out
  3. Pull the doser and inspect the tip and mixer pipe for crystal buildup
  4. Run the OEM dosing quantity (cup) test and compare with spec
  5. Measure coil resistance and inspect the connector for DEF intrusion
  6. Soak light deposits off in warm water; replace the doser if spray or volume stays wrong

FAQ

What does SPN 3361 FMI 5 mean?

Aftertreatment 1 DEF Dosing Unit — current below normal or open circuit. Less current is flowing in an output or sensor circuit than expected, which usually means the circuit is open.

Is SPN 3361 FMI 5 serious?

A doser that is stuck, clogged or not firing means NOx is not being reduced, and inducement derates will follow. Repair soon.

What should I check first for SPN 3361 FMI 5?

Inspect the connector and harness for this circuit: corrosion, water, chafing, backed-out pins; Check the reference voltage, ground and signal at the component per OEM pin-out; Pull the doser and inspect the tip and mixer pipe for crystal buildup.