SPN 647 FMI 4 — Fan drive voltage low
What it means: Fan drive voltage low.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Start with the most likely cause: Short to ground.
Don't risk it — look up listed providers near you and give them this SPN/FMI when you call.
Listed providers nearest Louisville, KY
Closest first. Tell them SPN 647 FMI 4 and what the truck is doing. RoadService.app lists these providers and does not employ them or carry out the repair.
- 0.0 mi away — based in Louisville, KY · (502) 773-1159
- 0.0 mi away — based in Louisville, KY · (502) 447-1234
- 0.0 mi away — based in Louisville, KY · (502) 648-6725
Applies to: Paccar · Volvo
What SPN 647 FMI 4 means
Fan drive voltage low.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Short to ground
FAQ
Fan drive voltage low.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Short to ground.
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Related codes
Codes that commonly appear alongside SPN 647 FMI 4, or share the same subsystem.
- Fan drive — voltage high (SPN 647 FMI 3)
- Engine Protection — Power Derate Active (SPN 1569 FMI 31)
- Intake Manifold (Charge Air) Temp — High (SPN 105 FMI 0)
- Turbo Boost Pressure — High / Overboost (SPN 1127 FMI 16)
- Boost pressure high (SPN 102 FMI 0)
- Boost sensor — voltage low (SPN 102 FMI 4)
- Intake manifold temp — voltage high (SPN 105 FMI 3)
- Intake manifold temp — voltage low (SPN 105 FMI 4)
Same symptom: Running hot
Other codes that show up as coolant temperature climbing or a hot-engine lamp.
- Coolant level — low (SPN 111 FMI 1) · Cooling
- Engine Coolant Over-Temperature Condition (P0217) · Cooling
- Engine Coolant Temperature — Too High (SPN 110 FMI 0) · Cooling
- Coolant temperature — moderately high (SPN 110 FMI 16) · Cooling
- Coolant Thermostat Below Regulating Temperature (P0128) · Cooling
- Engine Coolant Temperature Sensor 1 Circuit (P0115) · Cooling
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.