Safe to driveDrivable, but watch it yourself
J1939 code SPN 647. Below — how the fault is worded at the factory by Dongfeng and Renault Trucks, and what the second half of the code (FMI) means in the standard.
| FMI 3 | Short circuit to power or open circuit of the fan control drive |
| FMI 4 | Fan control output short circuit to ground |
| FMI 3 | Fan control circuit — short to positive (with the fan switched off). Repair: Check the fan hub and the wiring (B 4, B 9, B 14, B 22, B 23, B 34). Check the electrical components of the fan and the wiring (J 2/4, J 2/7, J 2/18, J 2/40). |
| FMI 4 | Fan control circuit — short to ground (with the fan switched on). Repair: Check the fan hub and the wiring (B 4, B 9, B 14, B 22, B 23, B 34). Check the electrical components of the fan and the wiring (J 2/4, J 2/7, J 2/18, J 2/40). |
| FMI 5 | Fan control circuit — open circuit. Repair: Check the fan hub and the wiring (B 4, B 9, B 14, B 22, B 23, B 34). Check the electrical components of the fan and the wiring (J 2/4, J 2/7, J 2/18, J 2/40). |
| SPN 647 FMI 3647/3 · 647.3 | voltage above normal or shorted high |
| SPN 647 FMI 4647/4 · 647.4 | voltage below normal or shorted to ground |
| SPN 647 FMI 5647/5 · 647.5 | current below normal or open circuit |
Safe to drive. Below — how much time you have and what happens if you keep going.
This is an electrical fault: the sensor or its wiring is lying, not the cooling system.
The temperature gauge is unreliable now and the fan may not kick in on time. Watch the coolant level and keep the engine off load on long climbs.
Let the engine cool — never open the expansion tank cap while hot. Then check the level and the hoses.
Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.