SPN 4334 FMI 2 is the Detroit diesel diagnostic trouble code for the DEF Metering Unit Pressure Sensor Drift on DD Series (EPA 2007-Current) engines. This 3 pages EPA10 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 4334 FMI 2 means
This code reports drift on the Diesel Exhaust Fluid (DEF) metering unit pressure sensor, enabled when the pressure limiting unit is off and evaluated after a five-hour engine-off period. It illuminates the MIL and is verified with the SCR Quantity Test.
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 4334 / FMI 2 (EPA10) |
| Monitored parameter | DEF pressure |
| Enabling condition | Pressure limiting unit off |
| Dash lamps | MIL |
| Verification | SCR Quantity Test |
| Pages | 3 pages |
| Source | Detroit Power Service Literature |
| Format | PDF, English |
Diagnostic steps in this manual
The procedure compares live pressures, then cleans and re-tests the metering unit.
- Connect the diesel diagnostic tool and compare DEF pressure against ambient (baro) and DEF air pressure.
- A reading within 2 PSI passes; otherwise remove the DEF metering unit air pressure sensor and re-test.
- Flush warm water through the metering unit cavities, reinstall the components and run the SCR air pressure test for 60 seconds.
- Use the recorded results to decide between replacing the DEF pressure sensor or servicing the metering unit.
Removal of the DEF pressure sensor, air pressure sensor and compressed-air supply screen follows Detroit Power Service Literature, and ACM software must be version 8.7 ZGS002 or higher. Because SPN 4334 FMI 2 is a factory-defined code, following the exact DEF metering unit pressure sensor 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 4334 FMI 2 guide
Heavy-duty technicians and workshop owners diagnosing DEF metering unit 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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