SPN 102 FMI 4Air IntakeHigh
Engine Intake Manifold Pressure (MAP) Sensor - Voltage Below Normal or Shorted Low
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Overview
Fault Code
SPN 102 / FMI 4
Category
Air Intake
Fault Type
sensor
FMI Category
voltage low
Severity
High
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: MAP sensor threaded into the intake manifold - typically on the intake manifold near the center of the engine. On Cummins X15: passenger side intake manifold. On Detroit DD15: driver side intake manifold. On PACCAR MX-13: driver side near throttle body.
Common Symptoms
- Boost pressure reading stuck at zero or below normal in live data
- Engine derate active - ECM defaults to conservative fueling without boost data
- Low power under load - ECM limits fueling without confirmed boost pressure
- Possible companion faults: SPN 102/3 (MAP sensor voltage high), SPN 641/7 (VGT fault)
- Turbocharger may be operating normally but ECM cannot confirm boost
- Black smoke possible - ECM over-fueling relative to available air
Root Causes
- MAP sensor signal wire shorted to ground - most common electrical cause
- MAP sensor internal failure - signal circuit shorted to ground internally
- MAP sensor connector - corroded or moisture-contaminated terminals
- MAP sensor 5V reference wire open circuit - no reference voltage causes low signal
- Damaged wiring harness - chafed wire grounding signal circuit
- MAP sensor vacuum/pressure port blocked - sensor not seeing actual manifold pressure
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Derate Behavior
Power Derate
Yes
Mileage / Regen Notes
MAP sensor failure increases with heat cycling and moisture exposure. Connector corrosion increases in high-humidity environments.
System Interactions
SPN 102 FMI 4 interacts with the following systems and may trigger cascading faults if not resolved promptly.
TSB Reference: Cummins TSB 4021756 - Intake Manifold Pressure Sensor Diagnosis; Detroit TSB 17-008 - MAP Sensor Voltage Low 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
X15: MAP sensor connector is exposed to intake air moisture - connector corrosion is common. Clean connector before replacing sensor. INSITE boost pressure test required.
Detroit
DD15: MAP sensor wiring harness routing near EGR cooler is a common chafe point. Inspect harness routing carefully.
PACCAR
MX-13: MAP sensor vacuum port can become clogged with oil mist from crankcase ventilation. Clean port before replacing sensor.
Volvo
MP8: MAP sensor 5V reference is shared with other sensors - low reference voltage affects multiple sensors simultaneously. Check reference voltage at multiple sensors if MAP reads low.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 102 FMI 4 — 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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