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Fault Code Reference

SPN 1079 FMI 16Engine Protection

Intake Manifold Temperature - Data Valid But Above Normal (Moderately Severe)

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Overview

Fault Code

SPN 1079 / FMI 16

Category

Engine Protection

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

No

Component Location: Intake manifold temperature sensor is mounted in the intake manifold downstream of the charge air cooler and EGR mixer.

Common Symptoms

  • Check engine light illuminated
  • Reduced engine power or derate active
  • High intake manifold temperature reading on scan tool
  • Engine runs rough or lacks power under load
  • Turbocharger boost pressure lower than normal
  • Increased exhaust gas temperatures
  • Poor fuel economy

Root Causes

  • Restricted or clogged charge air cooler reducing cooling efficiency Faulty intake manifold temperature sensor reading high EGR cooler failure or reduced cooling capacity Excessive EGR flow causing elevated intake temperatures Turbocharger overspeeding or compressor efficiency loss

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Derate Behavior

Power Derate

Yes

System Interactions

SPN 1079 FMI 16 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.

Deep-dive diagnostic page: SPN 1079 FMI 16 — 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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