Q: What does Freightliner fault code SPN 3031 FMI 3 mean?

SPN 3031 FMI 3 (Emissions / DEF): DEF Warning Light / Frozen Line Alert Fix: LOGIC: DEF Tank Temperature Sensor Circuit Failed High (Open Circuit). ACTION: Measure internal resistance across DEF tank level/temp sensor unit connector. Inspect tank harness for broken wires.

Q: What does Freightliner fault code SPN 3216 FMI 20 mean?

SPN 3216 FMI 20 (Emissions / NOx): Check Engine Light / Inducement Fix: LOGIC: Inlet NOx Sensor Drift High / Implausible Data. ACTION: Inspect inlet NOx sensor probe face for soot contamination. Check 24V supply and CAN link to sensor module; replace sensor if drift persists.

Q: What does Freightliner fault code SPN 3238 FMI 2 mean?

SPN 3238 FMI 2 (Emissions / NOx): Check Engine Light / Inducement Fix: LOGIC: Outlet NOx Sensor Not Ready After Dewpoint Enable Check. ACTION: Test outlet NOx sensor heater circuit power supply. Inspect exhaust tail section for moisture or damaged sensor heating element.

Q: What does Freightliner fault code SPN 3556 FMI 1 mean?

SPN 3556 FMI 1 (Emissions / DPF): Parked Regen Incomplete / Smoke Fix: LOGIC: Hydrocarbon (HC) Doser Pressure Low / Fuel Flow Restricted. ACTION: Disconnect HC doser fuel line. Perform doser valve volume output test via DiagnosticLink; replace clogged doser nozzle or manifold block.

Q: What does Freightliner fault code SPN 3610 FMI 2 mean?

SPN 3610 FMI 2 (Emissions / DPF): DPF Warning / Regenerations Stopped Fix: LOGIC: DPF Outlet Pressure Sensor Data Implausible / Out of Calibration. ACTION: Inspect DPF pressure sensor sampling tubes for moisture condensation or soot buildup. Verify sensor zero-point reading key-on engine off.

Q: What does Freightliner fault code SPN 4334 FMI 3 mean?

SPN 4334 FMI 3 (Emissions / DEF): DEF System Fault / Power Derate Fix: LOGIC: DEF Pressure Sensor Circuit Failed High (Voltage Above Limit). ACTION: Check for open ground circuit or short to 5V reference on DEF pressure sensor harness. Measure sensor signal voltage at ACM plug.

Q: What does Freightliner fault code SPN 4360 FMI 15 mean?

SPN 4360 FMI 15 (Emissions / SCR): SCR Efficiency Fault / MIL On Fix: LOGIC: Selective Catalytic Reduction (SCR) Inlet Temperature High. ACTION: Inspect SCR inlet temperature sensor wiring for signal drift. Verify DOC and DPF soot/ash buildup aren't creating thermal backpressure.

Q: What does Freightliner fault code SPN 520328 FMI 7 mean?

SPN 520328 FMI 7 (Emissions / DEF): DEF Pump Whine / System Fault Fix: LOGIC: DEF System Over-Pressurized (Pump Relief Valve Stuck). ACTION: Check DEF return line for urea crystallization blockages. Inspect DEF dosing unit internal pressure regulator valve for sticking.

Question 1

What does Freightliner fault code SPN 108 FMI 13 mean?

Accepted Answer

SPN 108 FMI 13 (Sensors / Air): Engine Sluggish / Black Exhaust Fix: LOGIC: Ambient Air Pressure (Baro) Signal Not Available via CAN.

ACTION: Check ambient pressure sensor mounted inside CPC/MCM module or cabin air intake block. Reflash or replace module if internal sensor failed.

Question 2

What does Freightliner fault code SPN 168 FMI 1 mean?

Accepted Answer

SPN 168 FMI 1 (Electrical): Multiple Random Faults / Hard Shift Fix: LOGIC: Battery Voltage Low (<10.5V on 12V System / <21V on 24V System).

ACTION: Load test chassis battery bank. Check alternator charging output under load and clean main chassis ground studs behind starter.

Question 3

What does Freightliner fault code SPN 3031 FMI 3 mean?

Accepted Answer

SPN 3031 FMI 3 (Emissions / DEF): DEF Warning Light / Frozen Line Alert Fix: LOGIC: DEF Tank Temperature Sensor Circuit Failed High (Open Circuit).

ACTION: Measure internal resistance across DEF tank level/temp sensor unit connector. Inspect tank harness for broken wires.

Question 4

What does Freightliner fault code SPN 3216 FMI 20 mean?

Accepted Answer

SPN 3216 FMI 20 (Emissions / NOx): Check Engine Light / Inducement Fix: LOGIC: Inlet NOx Sensor Drift High / Implausible Data.

ACTION: Inspect inlet NOx sensor probe face for soot contamination. Check 24V supply and CAN link to sensor module; replace sensor if drift persists.

Question 5

What does Freightliner fault code SPN 3238 FMI 2 mean?

Accepted Answer

SPN 3238 FMI 2 (Emissions / NOx): Check Engine Light / Inducement Fix: LOGIC: Outlet NOx Sensor Not Ready After Dewpoint Enable Check.

ACTION: Test outlet NOx sensor heater circuit power supply. Inspect exhaust tail section for moisture or damaged sensor heating element.

Question 6

What does Freightliner fault code SPN 3556 FMI 1 mean?

Accepted Answer

SPN 3556 FMI 1 (Emissions / DPF): Parked Regen Incomplete / Smoke Fix: LOGIC: Hydrocarbon (HC) Doser Pressure Low / Fuel Flow Restricted.

ACTION: Disconnect HC doser fuel line. Perform doser valve volume output test via DiagnosticLink; replace clogged doser nozzle or manifold block.

Question 7

What does Freightliner fault code SPN 3610 FMI 2 mean?

Accepted Answer

SPN 3610 FMI 2 (Emissions / DPF): DPF Warning / Regenerations Stopped Fix: LOGIC: DPF Outlet Pressure Sensor Data Implausible / Out of Calibration.

ACTION: Inspect DPF pressure sensor sampling tubes for moisture condensation or soot buildup. Verify sensor zero-point reading key-on engine off.

Question 8

What does Freightliner fault code SPN 4334 FMI 3 mean?

Accepted Answer

SPN 4334 FMI 3 (Emissions / DEF): DEF System Fault / Power Derate Fix: LOGIC: DEF Pressure Sensor Circuit Failed High (Voltage Above Limit).

ACTION: Check for open ground circuit or short to 5V reference on DEF pressure sensor harness. Measure sensor signal voltage at ACM plug.

Question 9

What does Freightliner fault code SPN 4360 FMI 15 mean?

Accepted Answer

SPN 4360 FMI 15 (Emissions / SCR): SCR Efficiency Fault / MIL On Fix: LOGIC: Selective Catalytic Reduction (SCR) Inlet Temperature High.

ACTION: Inspect SCR inlet temperature sensor wiring for signal drift. Verify DOC and DPF soot/ash buildup aren't creating thermal backpressure.

Question 10

What does Freightliner fault code SPN 520328 FMI 7 mean?

Accepted Answer

SPN 520328 FMI 7 (Emissions / DEF): DEF Pump Whine / System Fault Fix: LOGIC: DEF System Over-Pressurized (Pump Relief Valve Stuck).

ACTION: Check DEF return line for urea crystallization blockages. Inspect DEF dosing unit internal pressure regulator valve for sticking.

Freightliner Fault Codes

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Code	System	Symptom	Full fix
SPN 108 FMI 13	Sensors / Air	Engine Sluggish / Black Exhaust	View fix
SPN 168 FMI 1	Electrical	Multiple Random Faults / Hard Shift	View fix
SPN 3031 FMI 3	Emissions / DEF	DEF Warning Light / Frozen Line Alert	View fix
SPN 3216 FMI 20	Emissions / NOx	Check Engine Light / Inducement	View fix
SPN 3238 FMI 2	Emissions / NOx	Check Engine Light / Inducement	View fix
SPN 3556 FMI 1	Emissions / DPF	Parked Regen Incomplete / Smoke	View fix
SPN 3610 FMI 2	Emissions / DPF	DPF Warning / Regenerations Stopped	View fix
SPN 4334 FMI 3	Emissions / DEF	DEF System Fault / Power Derate	View fix
SPN 4360 FMI 15	Emissions / SCR	SCR Efficiency Fault / MIL On	View fix
SPN 520328 FMI 7	Emissions / DEF	DEF Pump Whine / System Fault	View fix
SPN 521049 FMI 31	Emissions	Speed Restricted to 5 MPH (Final Derate)	View fix
SPN 609 FMI 12	Computer / CAN	Dead Throttle / No-Start / No Crank	View fix
SPN 625 FMI 9	Communication	Engine Runs at Fixed Idle / Dash Alert	View fix