FC 418 — Water-In-Fuel Indicator – Above Normal (SPN 97 FMI 15) — Cummins ISX15
Diagnostic reference for Cummins ISX15 (2010–2017) FC 418.
What it means
The water-in-fuel sensor detected water in the fuel filter.1
Most likely causes
- Water actually present in the fuel/water separator or fuel filters from contaminated fuel or condensation. — The sensor is reporting water above the normal threshold. Typical on this platform is to drain the fuel/water separator and check fuel quality.1
- Water-in-fuel sensor or its wiring giving a false high reading. — A faulty sensor or wiring can cause the ECM to see water when none is present. Verify sensor operation and wiring integrity before assuming fuel contamination.1
- Improperly drained or reinstalled fuel/water separator allowing water to remain in the sensing area. — Residual water after service or a disturbed sensor can keep the indicator above normal. Confirm separator condition and sensor seating.1
How to diagnose
- Confirm active FC 418 with SPN 97 FMI 15 on the ISX15 CM2250/CM2350 ECM and note any accompanying fuel system codes.
- Inspect the fuel/water separator for visible water and check fuel quality; typical on this platform is to drain the separator and check fuel quality.
- Test the water-in-fuel sensor signal and wiring for correct resistance/voltage and intermittent faults to rule out a false high reading.
- Review recent fueling history, filter service, and separator maintenance for contamination or improper reassembly that could leave water in the sensing area.
Parts and tools you may need
- Fuel/water separator drain valve
- Water-in-fuel sensor
- Digital multimeter
- Fuel sample jar
- Cummins Insite or equivalent diagnostic tool
Tools you’ll need
- OBD-II scan tool — Reads active FC 418 with SPN 97 FMI 15 on the ISX15 CM2250/CM2350 ECM and shows accompanying fuel system codes.
- Digital multimeter — Tests the water-in-fuel sensor signal and wiring for correct resistance/voltage to rule out a false high reading.
- Fuel drain container — Collects drained fuel from the water-in-fuel separator to inspect for visible water and assess fuel quality.
- Inspection mirror — Allows visual check of the fuel/water separator and sensing area for residual water or improper reassembly.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| Wiring or connector repair | $10–$100 | 1–4 hrs | DIY with tools and a manual |
| Temperature or pressure sensor (coolant, intake air, oil, fuel temp) | $30–$150 | 0.3–1.5 hrs | Easy DIY |
| Fuel filter service | $60–$200 | 0.3–1 hrs | Easy DIY |
Typical US independent-shop figures; labor runs about $140–$200 per hour (dealers charge more). Confirm the diagnosis before buying parts.
When to see a pro
If water contamination is confirmed, have the fuel system professionally evaluated to prevent injector or high-pressure pump damage on the XPI common rail system. If the sensor tests good but the code persists, have the ECM data and wiring diagnosed by a qualified Cummins technician.
Check for recalls
Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.
Sources
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