Can I drive with SPN 94 FMI 4?

Usually yes for a short distance, but fix it soon. Warning faults like SPN 94 FMI 4 commonly escalate into torque derate if ignored. The scan-tool checks below help determine urgency.

How do I fix SPN 94 FMI 4?

Start with: Inspect sensor connector and wiring first (fast and common). Then follow the diagnostic steps and scan-tool checks on this page.

What tools help diagnose SPN 94 FMI 4?

A quality J1939 scan tool and, when available, Cummins INSITE for actuator tests and live data.

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Level: WarningCummins

SPN 94 FMI 4: Fuel delivery pressure sensor circuit voltage low – hard starts, surging, power loss

SPN 94 FMI 4: Fuel delivery pressure sensor circuit voltage low – hard starts, surging, power loss. For Cummins. Symptoms (3), causes (3), and fixes (3). What to check first to prevent derate and downtime.

Code	SPN 94 FMI 4
Severity	Warning
Applies to	Cummins
Can I drive?	Usually yes for a short distance, but fix it soon. Warning faults like SPN 94 FMI 4 commonly escalate into torque derate if ignored. The scan-tool checks below help determine urgency.

Symptoms

Likely causes

Fixes

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What does SPN 94 FMI 4 mean?

When SPN 94 FMI 4 sets, the ECM is indicating a fault condition that affects performance, protection strategy, or emissions (depending on calibration).

This page includes notes for Cummins when available.

Treat repeat faults as ACTIVE and diagnose using a scan tool and basic inspections before replacing parts.

How this system works (why SPN 94 FMI 4 happens)

Most modern fault logic is based on expected vs actual sensor readings, timing windows, and plausibility checks.

A single event might store a code, but repeated events across drive cycles are what typically trigger warnings, derate strategies, or inducement (emissions systems).

Your goal is to identify the failure mode (electrical, mechanical, sensor drift, or upstream cause) rather than “parts cannon” replacement.

Images for SPN 94 FMI 4 (location, common failures)

Common rail fuel injection system diagram — Common rail diagram (general). Fuel supply pressure problems can cause rail pressure issues.
Credit: Wikimedia Commons • License: Public Domain

Only use images you own or that have a license allowing commercial reuse (example: CC BY). Attribution alone is not permission.

Detailed guide for SPN 94 FMI 4

SPN 94 FMI 4 – Fuel delivery pressure voltage low

Winter adds a bonus layer: **fuel restriction and gelling** can make this code show up alongside real electrical problems.

What drivers usually report

Starts rough when cold
Feels like it’s starving for fuel on acceleration
Acts better after warming up (classic restriction clue)

Fix order that makes sense

1) Electrical checks at the sensor connector

2) Fuel filters and fuel quality

3) Lift pump supply pressure test

Location hint for SPN 94 FMI 4

Component location varies by OEM and chassis. Use your engine’s service manual to confirm the sensor/valve location before replacing parts.

Tip: Inspect connectors and harness routing before replacing parts.

Scan tool checks for SPN 94 FMI 4

Check status: ACTIVE vs INACTIVE / stored. If it’s not active, look at last occurrence conditions (freeze-frame if available).
Record companion codes. Fixing the “first” code often makes others disappear.
Clear and re-test under similar conditions. If it returns quickly, you have a repeatable fault (good for diagnosis).

If your tool can’t run actuator tests, you can still diagnose a lot with careful inspection + repeatability testing.

Step-by-step diagnostic for SPN 94 FMI 4

Visual inspection (fast wins). Harness routing, connector pins, hoses/lines (if applicable), and obvious damage.
Check fluid sanity. Not applicable unless your fault is fluid-related. Focus on inspections + repeatability.
Confirm the fault is ACTIVE. Stored-only faults can be old events.
Run actuator tests (if supported). Use Cummins INSITE (or a capable J1939 tool) to command tests when available.
Verify after repair. Clear codes, road test, confirm it stays inactive.

Decision guide (fast path) for SPN 94 FMI 4

If the fault is STORED only → inspect, clear, and monitor. If it returns, treat it as active.
If ACTIVE → check connector/harness first → then confirm sensor values and plausibility → then consider component testing.
If you have multiple codes → diagnose the earliest/most upstream code first.

Common misdiagnosis mistakes for SPN 94 FMI 4

Replacing sensors without checking wiring, grounds, and connector pin fitment.
Clearing codes repeatedly without confirming whether the fault is ACTIVE and repeatable.
Missing companion codes that point to the real upstream problem.

Will SPN 94 FMI 4 cause derate or inducement?

Warning aftertreatment faults often start as an emissions warning, then progress to torque derate if the fault remains active over multiple drive cycles. If ignored, many platforms can eventually enter inducement and severe speed limiting.

Exact behavior depends on ECM calibration and which companion faults are active.

“Do this first” checklist for SPN 94 FMI 4

Scan for companion/derate codes and record freeze-frame data (if available).
Inspect connectors, harness rub points, and pins for corrosion.
Check for other active faults that may be upstream causes (communications, sensors, air/fuel issues).
After repair, clear codes and confirm the fault stays inactive after a drive cycle.

Tools needed to diagnose SPN 94 FMI 4

Basic hand tools + good lighting for inspection
Multimeter for connector/power/ground checks (if wiring suspected)
Cummins INSITE (or equivalent scan tool) for actuator tests and live data

Prevention tips to avoid repeat SPN 94 FMI 4

Fix small wiring/connector issues early before they become repeat faults.
During service, inspect harness routing and clamp points near heat/vibration.
Don’t ignore intermittent faults. “Erratic” usually gets worse.

What to check first for SPN 94 FMI 4

Inspect connectors and harness near the affected component for corrosion, rubbing, or loose pins.
Check for upstream causes (communications, sensors, air/fuel issues).
Check for other active faults that may be upstream causes (communications, sensors, air/fuel issues).

If the fault repeats after clearing, diagnose it as ACTIVE. Many faults escalate into derate when ignored.