SPN 4094 FMI 18: EGR performance below normal – power loss, smoke, frequent regens. Symptoms (3), causes (3), and fixes (3). What to check first to prevent derate and downtime.
| Code | SPN 4094 FMI 18 |
|---|---|
| Severity | Warning |
| Applies to | Varies by OEM configuration (confirm your exact calibration) |
| Can I drive? | Usually yes for a short distance, but fix it soon. Warning faults like SPN 4094 FMI 18 commonly escalate into torque derate if ignored. The scan-tool checks below help determine urgency. |
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When SPN 4094 FMI 18 sets, the ECM is indicating a fault condition that affects performance, protection strategy, or emissions (depending on calibration).
OEM definitions can vary slightly, so confirm your exact meaning with your service manual or diagnostic tool.
Treat repeat faults as ACTIVE and diagnose using a scan tool and basic inspections before replacing parts.
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.
Drivers usually notice this as a “lazy” truck that keeps asking for regen. In winter, long idle time and short trips make soot build up faster.\n\n**Best approach:** verify airflow and EGR feedback first. Swapping parts without checking for leaks and sensor data is how you end up paying twice.
The DPF differential pressure sensor is usually mounted on/near the firewall or aftertreatment bracket. It connects to the exhaust via two small pressure tubes (pre- and post-DPF). Check the tubes for soot blockage, cracks, water intrusion, and heat damage.
Tip: Soot blockage or water in the DP tubes is a very common cause of erratic differential pressure readings.
If your tool can’t run actuator tests, you can still diagnose a lot with careful inspection + repeatability testing.
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.
If the fault repeats after clearing, diagnose it as ACTIVE. Many faults escalate into derate when ignored.
The videos below are embedded using YouTube’s official player. We do not host or claim ownership of this content. Use it as a visual reference and always confirm with diagnostics for your exact truck configuration.
Mechanic community notes for SPN 4094 FMI 18
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