SPN 520371 FMI 31: DPF regeneration inhibited due to conditions – regen will not initiate. Symptoms (3), causes (3), and fixes (3). What to check first to prevent derate and downtime.
| Code | SPN 520371 FMI 31 |
|---|---|
| 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 520371 FMI 31 commonly escalate into torque derate if ignored. The scan-tool checks below help determine urgency. |
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When SPN 520371 FMI 31 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.
This shows up when the system wants to regen but refuses to start because conditions are not right.\n\nIf you keep driving like nothing is happening, soot climbs until you get a real restriction/derate code.
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.
Mechanic community notes for SPN 520371 FMI 31
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