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Cummins SPN 108 FMI 3: Meaning, Causes & Fix

Barometric Pressure Sensor Voltage High — barometric pressure sensor signal above normal range, affecting altitude compensation and air-fuel ratio

Reviewed by ASE Certified Mechanics · Last updated July 08, 2026

Quick Answer

SPN 108 FMI 3 = Baro Pressure Sensor Voltage High
Severity: ⚠️ WARNING · System: Barometric Pressure Sensor · ✅ Can continue with caution

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Diagnostic Reference

Field Details
Code SPN 108 FMI 3
Protocol J1939 SPN: 108 FMI: 3
Component Barometric Pressure Sensor
Manufacturer Cummins
Engine Series ISX15
Severity ⚠️ WARNING
SAE Reference SAE J1939-73 Digital Annex — SPN 108, FMI 3

Possible Causes

  1. Barometric pressure sensor failure
  2. Sensor signal wire shorted to power
  3. Sensor connector corrosion
  4. ECM internal fault
  5. Wiring harness damage

Diagnostic & Repair Procedure

  1. Step 1: Test barometric pressure sensor voltage at connector
  2. Step 2: Compare sensor reading to known altitude/barometric pressure
  3. Step 3: Inspect wiring and connector for damage or corrosion
  4. Step 4: Replace sensor if reading is incorrect for altitude
  5. Step 5: Verify ECM ground connection is clean and tight

Frequently Asked Questions

Is this a false alarm or a real problem?

CHECK SOON codes are rarely false alarms. The ECM has detected a parameter outside normal operating range. Sensor malfunctions can sometimes trigger false readings, but the majority of CHECK SOON codes indicate a developing issue that will worsen if left unaddressed. Use a diagnostic scan tool to verify sensor readings before replacing expensive parts.

Can I diagnose this without a scan tool?

Basic visual inspection can be performed without a scan tool — check wiring harnesses for chafing, connectors for corrosion, and related components for physical damage. However, to verify the fault, view live sensor data, and confirm the repair, a heavy-duty diagnostic scan tool (or a compatible OBD-II adapter with J1939/J1708 support) is strongly recommended for accurate diagnosis.

How soon should I schedule service?

Schedule service within the next 1–3 operating days. While the vehicle can continue operating normally, delaying repair increases the risk of the fault escalating to CHECK NEXT STOP severity. Additionally, some CHECK SOON conditions are precursors to emissions system faults that will trigger a mandatory derate if not addressed in a timely manner.

Estimated Repair Cost

Typical repair: $100–800 (Parts: $50–500 + Labor: 1–3 hours) · Costs vary by make/model and location

Diesel Repair Cost & Downtime Estimator

Enter estimated labor hours to calculate repair cost and potential fleet downtime losses. Based on national average diesel shop rate of $150/hr and daily revenue loss of $800/day for a parked truck.

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Associated Symptoms

Loss Of Power Black Smoke

References & Further Reading

Data Provenance: This fault code definition is derived from SAE J1939 standards. SPN 108 FMI 3 is defined in SAE J1939-73 Digital Annex. Diagnostic procedures sourced from Cummins OEM technical service documentation. Not for safety-critical decisions. Consult a certified diesel mechanic before performing any repair. See our full disclaimer.