SPN 4374: Detroit DEF Pump Speed Diagnostics
What SPN 4374 identifies
SPN 4374 concerns DEF pump speed. This page's examples are Detroit GHG14. For FMI 0, the cited bulletin identifies a system in which pump speed is too high for the pressure being delivered. High speed does not mean high DEF pressure. Detroit 5 21-14 (May 2014)
Documented SPN/FMI examples
Scroll horizontally to see the application and source.
| SPN / FMI | OEM FC | Meaning | Application / source |
|---|---|---|---|
4374 / 0 | — | Pump runs too fast for delivered pressure | Detroit DD GHG14 Detroit 5 21-14 (May 2014) |
4374 / 3 | — | Pump-speed signal above measurement range | Detroit GHG14 Detroit 1 11-13 (January 2013) |
4374 / 4 | — | Pump-speed signal below measurement range | Detroit GHG14 Detroit 1 11-13 (January 2013) |
Examples only; a dash means no separate FC is supplied here. *See source applicability below; a model name alone does not establish calibration coverage.
The GHG14 FMI 0 bulletin documents a 25% derate. Apply that reaction only within the cited scope; another FMI or calibration can have a different reaction. Detroit 5 21-14 (May 2014)
Use the matching pump test
- Save related faults and identify the installed dosing system. For signal faults, follow the electrical branch; for FMI 0, evaluate the speed-versus-pressure condition.
- Inspect the supply path, lines, filter and dosing system as required by the OEM sequence. A pump-related fault does not isolate the failed component.
- Run the specified service routine and record its actual pass/fail result. A dosing quantity test and a pressure test are not interchangeable.
- Repair the established cause, then repeat the required verification. Use the OEM procedure for opening, depressurizing and testing the DEF system.
Sources and applicability
Source check: September 12, 2026. These are documented examples. Confirm the engine serial number, software calibration and current OEM instructions before using a test or repair procedure.
- Detroit 5 21-14 (May 2014) — GHG14 DD: 4374/0, pump speed compared with DEF pressure.
- Detroit 1 11-13 (January 2013) — GHG14: 4374/0, /1, /3 and /4; use the procedure for the actual FMI.
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