What are the symptoms of SPN 102 FMI 3?

Engine derate active — ECM defaults to limp mode without valid boost signal. Black smoke from exhaust — ECM may over-fuel without boost feedback. Reduced power and poor throttle response. Turbocharger over-boost or under-boost condition possible. Hard start in cold weather — boost signal used for fueling calculations. Active regen may be inhibited without valid boost data

What causes SPN 102 FMI 3?

Boost pressure sensor shorted to 5V reference — signal wire touching reference wire. Boost pressure sensor internal failure — sensor output stuck high. Boost pressure 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 102 FMI 3?

Full step-by-step DVOM tests, electrical procedures, and connector pinout data for SPN 102 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 102 FMI 3Air/BoostHigh

Engine Intake Manifold Pressure (Boost) — Voltage Above Normal or Shorted High

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Overview

Fault Code

SPN 102 / FMI 3

Common Symptoms

Engine derate active — ECM defaults to limp mode without valid boost signal
Black smoke from exhaust — ECM may over-fuel without boost feedback
Reduced power and poor throttle response
Turbocharger over-boost or under-boost condition possible
Hard start in cold weather — boost signal used for fueling calculations
Active regen may be inhibited without valid boost data

Root Causes

Boost pressure sensor shorted to 5V reference — signal wire touching reference wire
Boost pressure sensor internal failure — sensor output stuck high
Boost pressure 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

Yes

Mileage / Regen Notes

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

System Interactions

SPN 102 FMI 3 interacts with the following systems and may trigger cascading faults if not resolved promptly.

TSB Reference: Cummins TSB 4021801 — Intake Manifold Pressure Sensor Diagnosis; Detroit TSB 14-019 — MAP Sensor Circuit Diagnosis; PACCAR TSB AI-002 — Boost Pressure 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: Boost sensor connector corrosion is common on ISX engines. Clean connector before replacing sensor. INSITE boost sensor test required.

Detroit

DD15/DD13: MAP sensor harness routing near charge air cooler is a known chafe point. Inspect harness at CAC outlet. DDDL MAP sensor test required.

PACCAR

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

Volvo

MP8: Boost sensor connector moisture intrusion is common. Inspect connector seal. PTT boost sensor 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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