SPN 4331 FMI 18 is the Detroit diesel diagnostic trouble code for the DEF Dosing Quantity Low on DD Series (EPA 2007-Current) engines. This 2 pages GHG14 PDF documents the code description, monitored parameters, dash-lamp and engine-reaction data, and the diagnostic routine drawn from Detroit Power Service Literature.
What SPN 4331 FMI 18 means
This code indicates that the DEF pump speed is high compared with the DEF quantity actually delivered. The CEL lamp stays on until the fault is resolved, and a log file should be kept if Detroit Customer Assistance is required.
Official document details
| Brand | Detroit |
|---|---|
| Model coverage | DD Series (EPA 2007-Current), also cross-referenced on Series 60 (DDEC VI, EPA 2007) |
| System / group | Diagnostic trouble codes (DTCs) |
| Fault code | SPN 4331 / FMI 18 (GHG14) |
| Monitored parameter | DEF pump speed vs delivered quantity |
| Dash lamps | CEL |
| Verification | DEF Quantity Test service routine |
| Pages | 2 pages |
| Source | Detroit Power Service Literature |
| Format | PDF, English |
Diagnostic steps in this manual
The document checks DEF quality, dosing volume and pump values before condemning any part.
- Repair SPN 3364 (improper DEF quality) first if it is also present, then inspect all DEF supply lines for kinks, cracks and leaks.
- Run the DEF Quantity Test and confirm the dispensed volume is between 102 and 138 mL.
- Check DEF concentration with a refractometer from DEF Test Kit W060589001900; it should read 28 to 36%.
- Compare pump speed (750 to 1800 RPM) and DEF pressure (9000 to 11000 mbar) with normal values before replacing the doser valve or DEF pump.
DEF Test Kit W060589001900 and Detroit Power Service Literature flushing procedures are referenced throughout the routine. Because SPN 4331 FMI 18 is a factory-defined code, following the exact DEF dosing quantity sequence and the Detroit Power Service Literature references is what keeps the repair verifiable.
Applicable trucks and engines
This procedure applies to Detroit DD Series diesel engines built to EPA 2007 and later standards, and Detroit cross-references the same code on Series 60 (DDEC VI, EPA 2007) engines. Confirm exact coverage on the Detroit Diesel official website.
Who needs this SPN 4331 FMI 18 guide
Heavy-duty technicians and workshop owners diagnosing DEF dosing problems use this guide to follow the factory troubleshooting steps instead of guessing. The full PDF is available in the DiagTechPro manuals library, with a free account required to download.
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