SPN 677 FMI 4 is the Detroit DD Series diagnostic fault code that identifies Engine starter relay circuit failed low. This DiagTechPro reference summarizes the official 1-page 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 | Engine starter relay circuit failed low |
| Published source | TruckFaultCodes.com, Copyright © 2017 |
| Pages | 1 |
| File size | 0.2 MB |
| Format | |
| Language | English |
SPN 677 FMI 4 diagnostic overview
This Detroit sheet covers an engine starter relay circuit that failed low. The technician disconnects the Motor Control Module (MCM) 21-pin connector, removes the engine starter relay, and measures the resistance between pin 21 of the MCM 21-pin connector and the relay, using the OEM wiring schematic for the correct pin location. If the resistance is greater than 3 ohms the open circuit is repaired; otherwise the engine starter relay is replaced per OEM procedures.
Document table of contents
- Fault code identification
- MCM 21-pin resistance measurement
- OEM pin-location note
- Repair or engine starter relay replacement
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 engine starter relay wiring at the Motor Control Module 21-pin connector. For the OEM wiring schematics referenced in this procedure, see the official Detroit engine manufacturer site.
Who needs the SPN 677 FMI 4 manual
Workshop technicians and fleet owners using the diesel diagnostic tool to read Detroit fault codes and test the engine starter relay 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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