SPN 172 FMI 0Turbo/AirHigh
Intake Manifold Air Temperature — Data Valid But Above Normal
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Overview
Fault Code
SPN 172 / FMI 0
Category
Turbo/Air
Fault Type
sensor
FMI Category
above normal
Severity
High
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: IAT sensor in intake manifold — typically driver side, near front of engine. CAC mounted in front of radiator.
Common Symptoms
- Intake air temperature warning active
- Engine derate under load in hot conditions
- Charge air cooler efficiency fault may be co-active
- Reduced power on grades or in high ambient temperatures
Root Causes
- Charge air cooler (CAC) plugged with debris, bugs, or road grime
- CAC boost leak — hot compressed air bypassing cooler
- CAC internal leak — exhaust gas contaminating charge air
- Ambient temperature extremely high combined with heavy load
- IAT sensor failure reading high
- Turbocharger compressor wheel damage causing excessive heat
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Derate Behavior
Power Derate
Yes
Mileage / Regen Notes
Seasonal — higher frequency in summer months and high-altitude operations.
System Interactions
SPN 172 FMI 0 interacts with the following systems and may trigger cascading faults if not resolved promptly.
TSB Reference: Cummins TSB 4021756 — Charge Air Cooler Inspection and Pressure Test Procedure
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
X15: IAT derate threshold is 230°F. CAC cleaning with compressed air and degreaser recommended at every PM.
Detroit
DD15: Check EGR cooler for internal leak — EGR cooler failure can contaminate charge air and raise IAT.
PACCAR
MX-13: Inspect CAC outlet pipe coupler — known failure point causing boost leak and high IAT.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 172 FMI 0 — 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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