SPN 110 FMI 3ThermalHighRegen Inhibit
Engine Coolant Temperature — Voltage Above Normal or Shorted High
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 110 / FMI 3
Category
Thermal
Fault Type
electrical
FMI Category
voltage high
Severity
High
Derate Risk
Yes
Regen Inhibit
Yes — active regen blocked
Inducement Risk
No
Component Location: Engine coolant temperature sensor threaded into engine block, cylinder head, or coolant crossover pipe. Location varies by OEM: Cummins ISX — cylinder head coolant crossover; Detroit DD15 — front of engine block; PACCAR MX-13 — cylinder head; Volvo MP8 — coolant crossover pipe.
Common Symptoms
- Engine derate active — ECM defaults to limp mode without valid coolant temp signal
- Active regen inhibited — DPF regeneration disabled without valid coolant temp
- Temperature gauge may read maximum or erratic on dash
- Fan may run at full speed — ECM commands cooling fan on without valid temp signal
- Cold start fueling incorrect — ECM cannot calculate proper warm-up enrichment
- Possible overheat warning even when engine is cold
Root Causes
- Coolant temperature sensor shorted to 5V reference — signal wire touching reference wire
- Coolant temperature sensor internal failure — sensor output stuck high
- Coolant temperature sensor connector damage — pin pushed back or shorted
- Wiring harness short to voltage — signal wire contacting power source
- ECM analog input circuit fault — internal ECM failure (rare)
- Incorrect sensor installed — wrong sensor part number causing out-of-range signal
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Derate Behavior
Power Derate
Yes
Active Regen Inhibited
This fault prevents the DPF from completing an active regeneration cycle. DPF soot load will increase until the fault is resolved.
Mileage / Regen Notes
ECT sensor failure risk increases with age and heat cycling. Connector corrosion increases in high-humidity environments.
System Interactions
SPN 110 FMI 3 interacts with the following systems and may trigger cascading faults if not resolved promptly.
TSB Reference: Cummins TSB 4021789 — Engine Coolant Temperature Sensor Diagnosis; Detroit TSB 13-011 — ECT Sensor Circuit Diagnosis; PACCAR TSB TH-001 — Coolant Temperature Sensor Fault Diagnosis
Common Diagnostic Mistakes
Replacing the sensor without verifying wiring continuity and supply voltage first.
Clearing codes without identifying and resolving the root cause — the fault will return.
Ignoring related active faults — cascading faults often share a root cause.
Skipping the connector inspection — corrosion and damaged pins are a leading cause of sensor faults.
Condemning the ECM before exhausting all wiring and component tests.
OEM Notes
Cummins
ISX/X15: ECT sensor connector corrosion is common. Clean connector before replacing sensor. INSITE ECT sensor test required.
Detroit
DD15/DD13: ECT sensor harness routing near exhaust manifold is a known chafe point. Inspect harness at exhaust area. DDDL coolant temp test required.
PACCAR
MX-13: ECT sensor signal wire shorted to 5V reference is a known failure mode. Inspect connector carefully. DAVIE4 ECT test required.
Volvo
MP8: ECT sensor connector moisture intrusion is common. Inspect connector seal. PTT coolant temp test required.
Related Faults in This Category
OEM System Resources
ASE Training Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 110 FMI 3 — Full FSM Sequence & Repair Steps — includes wiring notes, sensor specs, and gated repair procedures.
Authority References
Diagnostic procedures on this page are informed by OEM service literature and industry standards.
Cummins QuickServe OnlineOfficial Cummins service manuals, fault code lookup, and TSB database.Detroit Diesel DiagnoCentralDetroit Diesel diagnostic procedures, DDDL documentation, and service literature.PACCAR MX Engine ServicePACCAR MX-11 and MX-13 engine service documentation and DAVIE diagnostic guides.Volvo/Mack Tech ToolVolvo and Mack engine fault code reference and PTT/Tech Tool diagnostic procedures.ASE — Diesel Truck Technician CertificationNational Institute for Automotive Service Excellence — T2 Diesel Engines certification standards.EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx standards.
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