Safe to driveTo the nearest safe stop
J1939 code SPN 1079. Below — how the fault is worded at the factory by Ford Trucks, International, Isuzu, KAMAZ, Renault Trucks and SITRAK, and what the second half of the code (FMI) means in the standard.
Ford TrucksInternationalIsuzuKAMAZRenault TrucksSITRAK
Ford Trucks/Ecotorq writes fault numbers in its own format: the code in the table below is a Ford code (hexadecimal, zero-padded), not a J1939 SPN. It matches the standard only where the signal itself is standard, and usually matches the title of this page by digit alone.
| FMI 3 | Connector or wiring harness defective (short circuit between AU1 and VPSx/AIMx, short circuit between Erx and VPSx/AIMx, short circuit between EU1 and VPSx/AIMx), IT-ECU defective |
| FMI 4 | Connector or wiring harness defective short circuit between AU1 and VMGx/vehicle ground), IT-ECU defective |
| FMI 0 | Vref Sensor Supply Voltage — 5V Sensor Supply Above Normal Range |
| FMI 1 | Vref Sensor Supply Voltage — 5V Sensor Supply Below Normal Range |
| FMI 2 | Voltage fault in 5-V power supply 1 (P1631) |
| FMI 3 | Sensor supply voltage, branch 1 |
| FMI 4 | Sensor supply voltage, branch 1 |
| FMI 14 | EECU common supply (+5 V). Repair: Replace the EECU. |
| FMI 3 | High voltage on SVE1 |
| FMI 4 | Low voltage on SVE1 |
| FMI 31 | SVE1/2 tracking voltage difference out of range |
Safe to drive. Below — how much time you have and what happens if you keep going.
The electrical system is not holding voltage. While the engine runs the alternator carries it; shut it off and you may not restart.
Next the lights go, then modules start dropping out and false codes appear all over the truck. Get to somewhere with help without shutting the engine down.
That said, the manufacturer flags this code as critical — if in doubt, it is safer to stop and check on the spot.
Check the battery terminals and earth strap — corrosion and loose clamps throw false codes all over the truck. Running voltage should be 27–29 V.
Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.