What are the symptoms of SPN 1077 FMI 2?

Intermittent or erratic intake manifold air temperature readings in ECM data. MIL or Check Engine Light illuminated. Engine derate or power reduction event. Possible hard start or rough idle in cold conditions. Fault code active or inactive cycling without clear pattern. Possible inhibited or delayed DPF regeneration cycle

What causes SPN 1077 FMI 2?

Corroded, damaged, or loose connector at the intake manifold air temperature sensor. Faulty or out-of-range intake manifold air temperature (IMAT) sensor. Chafed, shorted, or open wiring harness between sensor and ECM. Water intrusion into sensor connector causing intermittent resistance shift. Poor ECM ground causing reference voltage instability. Failed or cracked sensor element due to heat cycling. ECM software fault or calibration mismatch

How do I diagnose SPN 1077 FMI 2?

Full step-by-step DVOM tests, electrical procedures, and connector pinout data for SPN 1077 FMI 2 are available inside the AI Diesel Tech guided diagnostic session. The AI walks you through every test — one step at a time.

SPN 1077 FMI 2Engine Protection

Intake Manifold Air Temperature Sensor - Data Erratic, Intermittent or Incorrect

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Overview

Fault Code

SPN 1077 / FMI 2

Common Symptoms

Intermittent or erratic intake manifold air temperature readings in ECM data
MIL or Check Engine Light illuminated
Engine derate or power reduction event
Possible hard start or rough idle in cold conditions
Fault code active or inactive cycling without clear pattern
Possible inhibited or delayed DPF regeneration cycle

Root Causes

Corroded, damaged, or loose connector at the intake manifold air temperature sensor
Faulty or out-of-range intake manifold air temperature (IMAT) sensor
Chafed, shorted, or open wiring harness between sensor and ECM
Water intrusion into sensor connector causing intermittent resistance shift
Poor ECM ground causing reference voltage instability
Failed or cracked sensor element due to heat cycling
ECM software fault or calibration mismatch

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

Mileage / Regen Notes

FMI 2 on SPN 1077 may inhibit or delay active DPF regeneration due to inaccurate intake air temperature data used in regen calculations; some platforms will block regen entirely until sensor signal is validated as stable and within range.

System Interactions

SPN 1077 FMI 2 interacts with the following systems and may trigger cascading faults if not resolved promptly.

ECM communication — J1939 network faults can affect all connected modules

Engine protection — ECM may trigger derate to prevent damage

Aftertreatment — engine protection derates can affect regen strategy

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.

Related Faults in This Category

SPN 1569-31Engine Protection Derate SPN 100-1Oil Pressure Low SPN 190-0Engine Speed High SPN 111-4Coolant Level Sensor 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

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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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