Code Details
| Display code | SPN 94 FMI 1 |
|---|---|
| SPN | 94 |
| FMI | 1 |
| OEM code | None listed |
| Manufacturer | Detroit Diesel |
| System | Engine �?fuel system |
| Component | Fuel lift pump / fuel filter / fuel supply circuit |
| Source address | Unknown or not applicable |
| Severity | high |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-12 |
Plain-English Meaning
The DD15 uses a low-pressure lift pump to feed fuel to the high-pressure pump. SPN 94 FMI 1 means the fuel delivery pressure is too low for proper HP pump operation. On a Freightliner Cascadia or Western Star 5700XE equipped with the DD15, this fault typically points to a clogged fuel filter, a weak lift pump, or an air leak in the supply circuit. Low delivery pressure starves the HP pump, causing loss of rail pressure and engine power reduction. On Freightliner Cascadia and Western Star trucks with the DD15, the fuel delivery pressure sensor monitors the low-pressure fuel supply entering the CP4.2 high-pressure pump. DiagnosticLink displays fuel delivery pressure in real time and records the pressure at fault trigger time. The DD15 secondary fuel filter, located between the primary filter and the CP4.2 pump, should be inspected first because a restricted secondary filter is the most common cause of below-normal fuel delivery pressure on high-mileage Cascadia trucks. A delivery pressure that only drops below normal under high-load conditions indicates a marginal restriction, which becomes progressively worse as filter load increases.
SPN 94 FMI 1 is Fuel Delivery Pressure below normal operating range. On Detroit DD15 with MCM2.0, the ECM monitors fuel delivery pressure continuously. DiagnosticLink displays this value in live data and can help distinguish between a filter restriction (pressure drops under load) and a lift pump failure (pressure is consistently low regardless of demand).
Common Symptoms
- Power loss under load �?may feel like a sudden derate
- Hard start or extended crank
- Rough idle or hesitation
- SPN 157 (fuel rail pressure) may appear simultaneously
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Clogged primary fuel filter
- Lift pump worn or failing
- Air ingestion from a supply line fitting or low fuel level
- Restricted or kinked fuel supply line from tank
- Fuel delivery pressure sensor fault
First Checks
- Replace the primary fuel filter �?the most common fix for SPN 94 FMI 1 on the DD15
- Connect DiagnosticLink and monitor fuel delivery pressure under idle and load conditions
- Check for air in the fuel return line (clear lines allow visual inspection)
- Inspect the supply line from the fuel tank for kinks, soft collapse, or restriction
- If fuel delivery pressure remains low after filter replacement, test lift pump output with a manual gauge
- Inspect the secondary fuel filter and replace if at or past the service interval
- Monitor fuel delivery pressure at idle and under load in DiagnosticLink to characterize the restriction pattern
Can I Keep Driving?
Reduced power under load. The DD15 may enter a derate to protect the fuel system. Address promptly.
Related Codes
Related Lookup Pages
Sources
- Detroit Diesel Service and Diagnostic Resources — Public Reference Detroit Diesel (Daimler Truck North America) · oem · accessed 2026-06-11 · confidence medium
Source: Detroit Diesel (Daimler Truck North America), Detroit Diesel Service and Diagnostic Resources — Public Reference. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - DiagnosticLink Detroit Diesel Corporation · oem · accessed 2026-05-05 · confidence medium
Source: Detroit Diesel Corporation, DiagnosticLink. 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
Does the Detroit DD15 have an internal lift pump or an external frame-mounted pump?
The DD15 fuel system uses a gear-driven lift pump that is part of the engine assembly, not a separate frame-mounted electric pump. This means lift pump service is an engine-level repair. DiagnosticLink and Detroit service documentation specify the access procedure and pressure test method for the specific model year.
Can a partially clogged secondary filter cause SPN 94 FMI 1 on the DD15?
Yes. The secondary fuel filter is a common restriction point and should be replaced along with the primary filter when this fault appears. On GHG17 DD15 engines with an updated filter system, confirm the correct filter specification for the model year to avoid using a filter with incorrect micron rating.
Can I drive a Freightliner Cascadia with DD15 SPN 94 FMI 1 to a dealer?
Low fuel delivery pressure reduces HP pump life and can cause injector damage from fuel starvation. Short-distance driving to a service facility is typically possible if the engine is not derating severely, but continued operation under load is not recommended. The DD15 will activate a derate if rail pressure falls critically low.