What are the symptoms of SPN 105 FMI 3?

Engine derate possible — ECM may limit fueling without valid intake air temp. Intake air temperature gauge reads maximum or erratic. Cold start fueling may be incorrect — ECM cannot calculate proper enrichment. Turbocharger over-boost protection may be affected. Active regen timing may be affected without valid intake temp data

What causes SPN 105 FMI 3?

Intake manifold temperature sensor shorted to 5V reference — signal wire touching reference wire. Intake manifold temperature sensor internal failure — sensor output stuck high. Intake manifold 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

How do I diagnose SPN 105 FMI 3?

Full step-by-step DVOM tests, electrical procedures, and connector pinout data for SPN 105 FMI 3 are available inside the AI Diesel Tech guided diagnostic session. The AI walks you through every test — one step at a time.

SPN 105 FMI 3Air/BoostModerate

Engine Intake Manifold Temperature — Voltage Above Normal or Shorted High

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Overview

Fault Code

SPN 105 / FMI 3

Common Symptoms

Engine derate possible — ECM may limit fueling without valid intake air temp
Intake air temperature gauge reads maximum or erratic
Cold start fueling may be incorrect — ECM cannot calculate proper enrichment
Turbocharger over-boost protection may be affected
Active regen timing may be affected without valid intake temp data

Root Causes

Intake manifold temperature sensor shorted to 5V reference — signal wire touching reference wire
Intake manifold temperature sensor internal failure — sensor output stuck high
Intake manifold 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

Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.

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Derate Behavior

Power Derate

Possible

Mileage / Regen Notes

IAT sensor failure risk increases with age and heat cycling. Connector corrosion increases in high-humidity environments.

System Interactions

SPN 105 FMI 3 interacts with the following systems and may trigger cascading faults if not resolved promptly.

TSB Reference: Cummins TSB 4021801 — Intake Manifold Temperature Sensor Diagnosis; Detroit TSB 14-019 — IAT Sensor Circuit 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: IAT sensor is often combined with MAP sensor in a single unit. If MAP sensor is also faulting, replace combined MAP/IAT sensor. INSITE IAT sensor test required.

Detroit

DD15: IAT sensor connector corrosion is common. Clean connector before replacing sensor. DDDL intake temp test required.

PACCAR

MX-13: IAT sensor signal wire shorted to 5V reference is a known failure mode. Inspect connector carefully. DAVIE4 IAT test required.

Volvo

MP8: IAT sensor connector moisture intrusion is common. Inspect connector seal. PTT intake temp test required.

Related Faults in This Category

SPN 5246-31SCR NOx Efficiency Low SPN 4364-18DEF Dosing Below Normal SPN 3251-0DPF Differential Pressure High SPN 157-18Fuel Rail Pressure Low

OEM System Resources

Cummins Fault Codes Detroit Diesel Fault Codes PACCAR Fault Codes Volvo Fault Codes Freightliner Fault Codes Mack Fault Codes

ASE Training Resources

Why ASE Certification Matters How ASE Tests Work ASE Study Tips ASE vs AI Diesel Tech Certification Paths Get Started with ASE

Diagnostic Engine v7.0

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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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