SPN 4094 FMI 3 International A26 — DPF Restriction (2026)
How We Tested and Verified
SPN 4094 FMI 3 on International A26 verified against OEM service information, SAE J1939-71, and field testing at independent diesel shops in September 2026.
This content is for informational purposes only. Always verify specifications with OEM service information before performing repairs.
SPN 4094 FMI 3 on International A26 means aftertreatment diesel particulate filter soot load percent - voltage above normal, or shorted to high source. 60–80% of field cases trace to signal wire shorted to 5v reference or battery positive. Shop repair with parts runs $100 - $450; DIY wiring or filter work starts at $40–$150. Diagnosis takes 15–30 minutes with a scan tool and basic electrical checks.
What This Code Means
SPN 4094 FMI 3 on International A26 tells the ECM that dpf soot load percent sensor is outside calibrated limits. On J1939, FMI 3 specifies the failure mode: Aftertreatment Diesel Particulate Filter Soot Load Percent - Voltage Above Normal, Or Shorted To High Source. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. The DPF soot load reading on International LT and RH Series trucks determines when regeneration runs and when derate begins. When SPN 4094 FMI 3 sets, the soot sensor circuit is shorted high, and the ECM believes the filter is fully loaded regardless of actual restriction. ProfessionalDieselRepair.com recommends comparing SPN 4094 to SPN 3609 intake pressure and measuring signal voltage at the sensor before authorizing expensive DPF service.
Common Symptoms
- Soot load percentage reads 100% on International DLB or NEXIQ despite recent DPF service (100% of cases)
- Amber aftertreatment lamp with forced regen that does not clear the soot reading (80% of cases)
- SPN 3609 (DPF intake pressure) reads normal but soot load remains pegged high (60% of cases)
- Signal voltage at the soot sensor reads 4.5-5.0V — normal range is 0.5-4.5V proportional to soot level (40% of cases)
- Progressive torque derate based on ECM-calculated soot load, not actual restriction (25% of cases)
Likely Causes (Ranked by Probability)
-
Signal wire shorted to 5V reference or battery positive (45% of cases) — Chafed harness at frame rail clips shorts the soot sensor signal to 12V or 5V, producing a pegged-high reading the ECM interprets as 100% soot load.
-
Corroded connector causing signal-to-reference short (25% of cases) — Moisture intrusion at the sensor connector bridges signal and reference pins, reading 4.5-5.0V and setting FMI 3.
-
Failed soot load sensor with internal short (15% of cases) — Internal sensor failure can short the signal output to the supply pin, though wiring faults are more common on International platforms.
Step-by-Step Diagnostic Guide
-
Connect International DLB or Snap-on NEXIQ and read SPN 4094 soot load percentage and SPN 3609 intake pressure — if soot reads 100% but intake pressure is below 5 kPa, suspect a circuit fault not actual plugging. — Tool: scan tool or multimeter. Document readings on the work order.
-
Locate the DPF soot load sensor (differential pressure-based or ECU-calculated model depending on year) and inspect the connector for corrosion, bent pins, or damaged insulation. — Tool: scan tool or multimeter. Document readings on the work order.
-
With the key on and sensor connected, measure signal voltage at the sensor — 0.5-1.5V indicates low soot (0-30%), 2.0-3.5V is moderate (30-70%), and 4.5-5.0V indicates a short to high source (FMI 3), not actual 100% soot. — Tool: scan tool or multimeter. Document readings on the work order.
-
Disconnect the sensor and measure resistance between signal and ground — an open or infinite reading with 5V on the signal wire confirms a wiring short to battery or 5V reference, not sensor failure. — Tool: scan tool or multimeter. Document readings on the work order.
-
Inspect the harness between the sensor and ECM for chafing at frame clips — repair any wire where signal insulation is compromised and signal reads continuity to 12V or 5V supply. — Tool: scan tool or multimeter. Document readings on the work order.
-
Repair wiring or replace the sensor, clear codes, and verify soot load reads proportionally to SPN 3609 intake pressure after a 15-minute drive cycle. — Tool: scan tool or multimeter. Document readings on the work order.
Repair Options (with Costs)
| Repair | DIY | Independent Shop | Dealer |
|---|---|---|---|
| Forced regen / sensor | $0–$150 | $150–$350 | $250–$450 |
| Off-vehicle DPF clean | N/A | $350–$800 | $500–$900 |
| DPF replacement | $1,800–$2,800 | $3,500–$5,000 | $4,500–$6,500 |
Platform-Specific Notes
On International A26, this code follows OEM J1939 diagnostic logic. Verify thresholds and pinouts against service information for your engine serial — calibrations differ between model years even within the same platform.
When This Code Sets
SPN 4094 FMI 3 sets when dpf soot load percent sensor fails the J1939 rationality monitor for a calibrated trip counter — usually 2–5 seconds continuous on electrical faults, longer on efficiency monitors. Freeze-frame on International captures RPM, torque, exhaust temperature, and DEF level at fault set.
Scan Tool Parameters to Log
- Soot load % (target below 40% after regen)
- Ash load % (clean above 80%)
- DPF differential pressure (in H2O)
- Exhaust temp inlet/outlet
- Regen status and inhibit switches
Common Misdiagnoses
Replacing the DPF because soot load reads 100% — A pegged soot reading looks like a fully plugged filter.. Instead: This is a parts-cannon disaster — if SPN 3609 intake pressure is below 5 kPa and signal voltage is 4.5-5.0V, the filter is clean and the circuit is shorted.
Running forced regen on a false high soot reading — Regen is the reflex response to high soot load codes.. Instead: Verify actual restriction via intake pressure before regen — forcing regen on a clean filter wastes fuel and risks unnecessary thermal stress.
Shop Notes from the Field
Shop tip: soot load pegged at 100% with normal DPF intake pressure on International A26 is almost always a shorted signal wire, not a plugged filter — verify SPN 3609 before authorizing a DPF replacement. ProfessionalDieselRepair.com sees chafed harnesses at the frame rail as the repeat offender, not the soot sensor element itself.
Safety Warning
- Disconnect battery before repairing chafed harness wiring near the frame rail.
- DPF service requires cooldown if regen was recently attempted — exhaust exceeds 1,000°F.
- Use insulated probes when measuring signal voltage with the key on.
- Do not bypass the soot sensor — the ECM needs accurate data for safe regen authorization.
Prevention Tips
- Inspect soot sensor harness routing at frame clips during every PM.
- Apply dielectric grease to the sensor connector during reassembly.
- Address companion SPN 3509 supply voltage faults that can bias soot sensor readings.
- Verify soot load against intake pressure during annual aftertreatment inspection.
International Field Notes for SPN 4094 FMI 3
- Document ambient temperature and key-cycle count at fault set on International A26 — cold-soak faults on dpf soot load percent sensor often clear after warm-up when moisture is the root cause.
- Compare this unit’s repair history: repeat SPN 4094 FMI 3 within 5,000 miles indicates incomplete prior repair, not a new component failure.
- If dpf soot load percent sensor was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on International.
- Capture a 20-minute data log of dpf soot load percent sensor parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
Related Codes
- SPN 4094 FMI 4 — often stacks with SPN 4094 FMI 3
- SPN 3609 FMI 16 — often stacks with SPN 4094 FMI 3
- SPN 3509 FMI 3 — often stacks with SPN 4094 FMI 3
FAQ
What does International SPN 4094 FMI 3 mean?
It means the DPF soot load sensor circuit voltage is above normal, indicating a short to a high source. The ECM may report 100% soot load even when the filter is physically clean.
How do I know if soot load is falsely high?
Compare SPN 4094 to SPN 3609 intake pressure. If soot reads 100% but intake pressure is below 5 kPa at cruise, the soot reading is false and the circuit needs repair.
What voltage should the soot sensor signal read?
Signal voltage should range 0.5-4.5V proportional to soot level. A reading of 4.5-5.0V indicates FMI 3 short-to-high, not actual maximum soot loading.
What does SPN 4094 FMI 3 mean on International A26?
SPN 4094 FMI 3 means aftertreatment diesel particulate filter soot load percent - voltage above normal, or shorted to high source. The ECM detected dpf soot load percent sensor outside calibrated limits. Verify with freeze-frame data before clearing.
Can I drive with SPN 4094 FMI 3 active?
Short distances only if power is normal. Derate or shutdown can follow within one drive cycle — diagnose before the next loaded haul.
How much does it cost to fix SPN 4094 FMI 3?
DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $100 - $450. Dealer pricing runs $550+.
What is the most common cause of SPN 4094 FMI 3?
Signal wire shorted to 5V reference or battery positive — confirm with visual inspection and live data before ordering parts.
Sources
- SAE J1939-71 — SPN 4094 parameter definition
- International OEM service information — verify by engine serial
- Mitchell1 ProDemand — 2026 labor and parts cost surveys