SPN 4334 FMI 3 is the Detroit diesel diagnostic trouble code for the DEF Pressure Sensor Circuit Failed High on DD Series (EPA 2007-Current) engines. This 2 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 3 means
This code sets when the Diesel Exhaust Fluid (DEF) pressure sensor circuit reads a failed-high signal. It lights the MIL and CEL and applies a 25% engine derate, verified at engine idle for one minute.
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 3 (EPA10) |
| Monitored parameter | DEF pressure sensor |
| Enabling condition | Always enabled |
| Dash lamps | MIL, CEL |
| Engine reaction | 25% derate |
| Verification | Engine idle (1 minute) |
| Pages | 2 pages |
| Source | Detroit Power Service Literature |
| Format | PDF, English |
Diagnostic steps in this manual
The document walks through a voltage-based check of the sensor circuit and its wiring to the ACM.
- Check whether SPN 4334/FMI 3, SPN 4335/FMI 3 and SPN 3510/FMI 3 are set together to isolate a shared circuit fault.
- Disconnect the DEF pressure sensor and, key on and engine off, measure the voltage at pin 1 on the harness side to ground.
- Above 5.0 V points to a short to battery, while below 4.75 V calls for a wire repair toward pin 100 of the ACM.
- A reading of 4.75 to 4.9 V confirms a failed sensor that is replaced per Detroit Power Service Literature.
Repairs reference ACM pins 99 and 100, and the ACM software must be at version 8.7 ZGS002 or higher before the codes are cleared. Because SPN 4334 FMI 3 is a factory-defined code, following the exact DEF pressure sensor circuit 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 3 guide
Heavy-duty technicians and workshop owners diagnosing DEF pressure sensor 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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