SPN 656 FMI 3 is the Detroit DD Series diagnostic fault code that identifies Injector cylinder #6 needle control valve abnormal operation (max). This DiagTechPro reference summarizes the official 7-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 | Injector cylinder #6 needle control valve abnormal operation (max) |
| Published source | TruckFaultCodes.com, Copyright © 2017 |
| Pages | 7 |
| File size | 0.7 MB |
| Format | |
| Language | English |
SPN 656 FMI 3 diagnostic overview
This Detroit EPA10/GHG14 sheet covers the injector cylinder #6 needle control valve abnormal operation (max), monitored continuously at idle and above, with MIL and CEL lamps and a 25% engine derate. The technician checks for related SPN 168 or 723 codes, reviews warranty history, warms the engine above 71°C (160°F), and inspects the rear fuel injector harness 14-pin connector. Resistance is measured on the two-piece fuel injector wiring harness and injector, then at the Motor Control Module (MCM) 120-pin connector, and a test MCM installed with extension harness J-49120 is road tested for 30 minutes.
Document table of contents
- Fault code description and enabling conditions
- Multiple-code and warranty checks
- Rear fuel injector harness 14-pin inspection
- Resistance measurements and test MCM
- Road test verification
Applicable truck models covered
This diagnostic applies to Detroit DD Series EPA10 and GHG14 diesel engines and is grouped under the Series 60 (DDEC VI – EPA 2007) DTCs. It covers cylinder #6 fuel injection on the two-piece two-filter and three-filter fuel systems. For the OEM wiring schematics referenced in this procedure, see the official Detroit engine manufacturer site.
Who needs the SPN 656 FMI 3 manual
Workshop technicians and fleet owners using the diesel diagnostic tool to read Detroit fault codes and test the needle control 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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