SPN 3509 FMI 4 is documented in this Detroit DD Series fault code reference PDF, which covers the 5V Sensor Supply Bank 1 Circuit Failed Low condition on Detroit engines. The 2-page document lists the fault description, the step-by-step troubleshooting sequence and the connector measurements a technician uses to confirm the repair.
Official document details
| Brand | Detroit |
|---|---|
| Model coverage | Detroit DD Series (EPA 2007-Current) GHG14 engines using the MCM2.1 |
| System / group | DD Series (EPA 2007-Current) / DTCs |
| Diagnostic code | FMI 4 / SPN 3509 |
| Year / revision | Source dated 2017 |
| Pages | 2 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification: SPN 3509, FMI 4
- 5V sensor supply bank 1 failed low
- Monitored parameter and pin table
- Component isolation with diagnostic tool
- Sensor-by-sensor disconnection
- Engine harness repair or MCM2.1 replacement
Applicable truck models and engines
This fault code applies to Detroit DD Series (EPA 2007-Current) GHG14 engines using the MCM2.1, and the DiagTechPro library also files it under the Series 60 (DDEC VI, EPA 2007) DTC set. The diagnostic references the Motor Control Module (MCM2.1) used on these Detroit powertrains. See the manufacturer’s Detroit official website for current engine specifications and dealer support.
SPN 3509 FMI 4 troubleshooting overview
The monitored parameter is the MCM2.1 5V internal power supply, and the document lists the affected MCM2.1 pins 58, 82, 117 and 85 with the sensors on each. With the diesel diagnostic tool connected and the ignition on, the technician disconnects each listed component in turn, such as the crankcase ventilator speed, fuel rail pressure, water pump speed, oil pressure, camshaft position, fan speed, EGR delta P and intake throttle valve, watching for the fault to clear. If none clears it, the MCM2.1 120-pin connector is disconnected to decide between harness repair and module replacement.
Who needs this SPN 3509 FMI 4 manual
Detroit-certified technicians, independent truck repair shops and fleet maintenance teams will use this reference to follow the factory diagnostic sequence with a diesel diagnostic tool before replacing any control module or sensor.
The full PDF is available in the DiagTechPro manuals library; a free account is required to download it, alongside the related Detroit Power Service Literature.
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