SPN 4374 FMI 1 is the Detroit Diesel diagnostic trouble code set when an over-pressurized DEF system is detected on DD Series (EPA 2007-current) engines. This 3-page troubleshooting sheet lists the fault definition, the relevant monitor or note data, and a numbered diagnostic routine that ends in the correct wiring or component repair. It is drawn from TruckFaultCodes.com (© 2017) and applies to the GHG14 emissions calibration.
Official document details
| Brand | Detroit Diesel |
|---|---|
| Model coverage | DD Series engines (EPA 2007-current) |
| System / group | DTCs — DEF dosing hydraulics |
| Suspect parameter (SPN) | SPN 4374 |
| Failure mode (FMI) | over-pressurized DEF system |
| Emissions calibration | GHG14 |
| Verification | SCR ADS self-check |
| Source / copyright | TruckFaultCodes.com, © 2017 |
| Pages | 3 |
| File size | 0.2 MB |
| Format / language | PDF / English |
SPN 4374 FMI 1 table of contents
The procedure walks through every DEF electrical connection in turn – the DEF metering unit, the DEF pump, the Chassis/Aftertreatment System 47-pin, and the ACM2.1 connectors – inspecting each for corroded, spread or unseated pins and moisture. It then isolates the hydraulic side: the DEF return line is diverted into a DEF-safe container and an SCR ADS self-check confirms flow, first at the metering unit and then at the tank. The DEF supply filter is checked for debris, and the sheet ends with staged replacement of the metering unit, return line, tank header, DEF pump or ACM2.1 as the tests dictate.
- Fault code header and log-file note
- Connector inspections (metering unit, pump, ATS 47-pin, ACM2.1)
- DEF return-line flow tests with SCR ADS self-check
- DEF supply filter and tank header inspection
- Staged component replacement
Applicable truck models
This sheet is part of the DD Series diagnostic trouble code library and addresses the DEF dosing hydraulic and electrical system. The SPN 4374 FMI 1 procedure applies to Detroit DD Series (EPA 2007-current) engines running the GHG14 calibration, and the same code index is cross-referenced under the Detroit Series 60 (DDEC VI, EPA 2007) fault-code set. For engine identification and warranty details, see the Detroit Diesel official site.
Who needs this SPN 4374 FMI 1 manual
It is built for technicians chasing an over-pressurized DEF condition, where the cause can be electrical, a blocked line or a failed metering unit on Detroit DD Series trucks. The ordered flow tests keep a shop from replacing the pump when a pinched return line is the real fault.
The full 3-page PDF is available in the DiagTechPro manuals library; a free account is required to download.
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