Code Details
| Display code | SPN 94 FMI 1 |
|---|---|
| SPN | 94 |
| FMI | 1 |
| OEM code | None listed |
| Manufacturer | Cummins |
| System | Engine �?fuel system |
| Component | Fuel delivery pump / fuel filter / fuel supply lines |
| Source address | Unknown or not applicable |
| Severity | high |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-12 |
Plain-English Meaning
The Cummins XPI (Xcelerator Pump Injector) fuel system uses a gear-driven low-pressure lift pump to supply fuel to the high-pressure pump. When the fuel delivery pressure drops below normal, the high-pressure pump cannot maintain adequate rail pressure, which leads to power loss, rough running, or a no-start condition. The most common causes on the ISX15 and X15 are a clogged primary fuel filter, a failing lift pump, or air ingestion from a leaking supply line or fitting.
SPN 94 FMI 1 is Fuel Delivery Pressure below the normal operating range. On Cummins CM2350 ISX15/X15, the ECM monitors fuel delivery pressure via a dedicated sensor upstream of the HP pump inlet. Insite displays fuel delivery pressure as a live parameter and sets this fault when the reading falls below the calibration threshold for the current fuel demand. FMI 1 indicates a valid reading �?the sensor is functional but reporting a below-normal value.
Common Symptoms
- Loss of engine power, particularly under heavy load
- Rough idle or engine stumble at low speed
- Hard starting or extended crank time
- SPN 157 FMI 18 (fuel rail pressure low) may appear alongside this code
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Primary or secondary fuel filter restriction �?most common cause
- Lift pump worn or failing, unable to maintain adequate supply pressure
- Air ingestion from a leaking supply line fitting, cracked primary filter housing, or low fuel level
- Restricted fuel supply line (kinked, collapsed, or frozen in cold weather)
- Fuel delivery pressure sensor fault
First Checks
- Replace the primary and secondary fuel filters if overdue �?a restricted filter is the most common cause of SPN 94 FMI 1
- Connect Cummins Insite and monitor fuel delivery pressure at idle and under load �?compare to the spec for the engine serial number
- Check for air bubbles in the clear return line (if visible) to diagnose air ingestion
- Inspect the fuel supply line from the tank to the lift pump for kinks, soft spots, or restriction
- If filters are new and pressure is still low, test lift pump output pressure with a mechanical gauge
Can I Keep Driving?
Loss of fuel delivery pressure will cause reduced power and may result in a derate or no-start. Address promptly to avoid fuel system damage from cavitation.
Related Codes
Related Lookup Pages
Sources
- Cummins INSITE Service Tool — Public Reference Documentation Cummins Inc. · oem · accessed 2026-06-11 · confidence medium
Source: Cummins Inc., Cummins INSITE Service Tool — Public Reference Documentation. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - QuickServe Online Cummins Inc. · oem · accessed 2026-05-05 · confidence medium
Source: Cummins Inc., QuickServe Online. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - SAE J1939 Standards Collection SAE International · official · accessed 2026-05-05 · confidence medium
Source: SAE International, SAE J1939 Standards Collection. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
How often should the Cummins ISX15 or X15 fuel filters be replaced?
Cummins specifies fuel filter replacement intervals in the engine operation and maintenance manual, typically tied to mileage or operating hours. High-sulfur or low-quality diesel can clog filters faster than normal. When SPN 94 FMI 1 is present, always replace both the primary and secondary fuel filters before performing further diagnosis �?this resolves the fault in the majority of cases.
Can SPN 94 FMI 1 on the Cummins X15 cause SPN 157 FMI 18 (low rail pressure) at the same time?
Yes. SPN 94 FMI 1 (low fuel delivery) and SPN 157 FMI 18 (low rail pressure) are related faults that frequently appear together. Low delivery pressure means the HP pump cannot build adequate rail pressure, so both codes result from the same root cause. Fix the delivery pressure fault first �?resolving it will usually clear the rail pressure fault as well.
What is the correct fuel delivery pressure specification for the Cummins ISX15 or X15?
The exact specification depends on engine serial number and calibration version. Cummins Insite and QuickServe Online provide the engine-specific fuel delivery pressure specification. As a general reference, ISX15 and X15 engines typically require lift pump delivery pressure in the range of 30�?5 psi depending on load conditions, but always confirm with the official specification for the specific engine.