SPN 677 FMI 2 is the Detroit DD Series diagnostic fault code that identifies Low or no voltage for the starter switch. This DiagTechPro reference summarizes the official 2-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 | Low or no voltage for the starter switch |
| Published source | TruckFaultCodes.com, Copyright © 2017 |
| Pages | 2 |
| File size | 0.2 MB |
| Format | |
| Language | English |
SPN 677 FMI 2 diagnostic overview
This Detroit sheet covers low or no voltage for the starter switch. The technician first checks whether the code is inactive; if it stays inactive after a restart the truck is released. If the fault is active, the Motor Control Module (MCM) 21-pin connector is disconnected and voltage is measured on pin 20 with the key in the crank position, looking for more than 11.5 volts. The Common Powertrain Controller (CPC) connector #1 is then checked on pin 18 for more than 11.5 volts, and the cause of any low or no voltage is repaired.
Document table of contents
- Fault code identification and status check
- MCM 21-pin voltage check on pin 20
- CPC connector #1 voltage check on pin 18
- Repair of low or no voltage cause
Applicable truck models covered
This diagnostic applies to Detroit DD Series (EPA 2007-Current) diesel engines across all model years, and is also grouped under the Series 60 (DDEC VI – EPA 2007) DTCs. It covers the starter switch supply through both the Motor Control Module and the Common Powertrain Controller. For the OEM wiring schematics referenced in this procedure, see the official Detroit engine manufacturer site.
Who needs the SPN 677 FMI 2 manual
Workshop technicians and fleet owners using the diesel diagnostic tool to read Detroit fault codes and test the starter switch 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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