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SPN 647 FMI 3 — Fan drive — voltage high
SeriousEnginePower derate likely — plan to stop soon
Applies to: Detroit · Volvo
Fan drive — voltage high.
Don't risk it — get a diesel tech on the truck.
Your SPN/FMI rides along, so nearby mechanics see the fault before they quote you.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Wire short to voltage
- Driver circuit
- Short to voltage
FAQ
What does SPN 647 FMI 3 mean?
Fan drive — voltage high.
How serious is SPN 647 FMI 3?
Serious — Power derate likely — plan to stop soon.
What's the most likely cause of SPN 647 FMI 3?
The most common cause is: Wire short to voltage. Other possibilities include Driver circuit; Short to voltage.
Can I keep driving with SPN 647 FMI 3?
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Throwing this code right now?
Find a mechanic or related guides
General diagnostic guidance for heavy-duty diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack). Not a substitute for a scan-tool diagnosis on your specific truck.