SPN 679 FMI 7 is the Detroit DD Series diagnostic fault code that identifies Pressure Limiting Valve, failed to close. This DiagTechPro reference summarizes the official 3-pages Detroit diagnostic sheet so a technician can confirm the condition before opening the truck, and it links to the full downloadable PDF.
Official document details
| Brand | Detroit |
| Model coverage | Detroit DD Series (EPA 2007-Current) diesel engines |
| System / Group | DD Series (EPA 2007-Current) / DTCs |
| Fault condition | Pressure Limiting Valve, failed to close |
| Published source | TruckFaultCodes.com, Copyright © 2017 |
| Pages | 3 |
| File size | 0.3 MB |
| Format | |
| Language | English |
SPN 679 FMI 7 diagnostic overview
This Detroit sheet describes a pressure limiting valve (PLV) that failed to close. The PLV opens when rail pressure rises above 1150 bar, and the Motor Control Module commands a lower rail pressure to force it shut; if the valve does not close, the code is set with MIL and CEL lamps and a 25% engine derate. Troubleshooting has the technician check for related codes, then monitor fuel rail pressure at idle and again at 1800 rpm; if pressure stays above 900 bar the needle return and injector lines are inspected, otherwise the PLV is replaced on the three-filter system per Power Service Literature.
Document table of contents
- Fault code description and enabling conditions
- Monitored parameter, dash lamps and engine reaction
- Troubleshooting steps (fuel rail pressure checks)
- Pressure limiting valve replacement reference
Applicable truck models covered
This diagnostic applies to Detroit DD Series (EPA 2007-Current) common-rail diesel engines across all model years, and is also listed under the Series 60 (DDEC VI – EPA 2007) group. It concerns high-pressure fuel rail control, so it is relevant wherever a three-filter fuel system is fitted. For the OEM wiring schematics referenced in this procedure, see the official Detroit engine manufacturer site.
Who needs the SPN 679 FMI 7 manual
Workshop technicians and fleet owners using the diesel diagnostic tool to read Detroit fault codes and test the pressure limiting valve and Motor Control Module wiring will need this sheet. The full step-by-step PDF is available in the DiagTechPro manuals library, and a free account is required to download it.
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