Safe to driveTo the nearest safe stop
J1939 code SPN 1089. Below — how the fault is worded at the factory by Ford Trucks, International, KAMAZ and Mercedes-Benz, and what the second half of the code (FMI) means in the standard.
Ford TrucksInternationalKAMAZMercedes-Benz
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 9 | Driveline CAN wiring defective, terminating resistor of driveline CAN bus defective, error in transmission control unit (EDC) |
| FMI 0 | Auxiliary Equipment Supply Pressure — Auxiliary Air Tank Sensor Reading Above Normal |
| FMI 1 | Auxiliary Equipment Supply Pressure — Auxiliary Air Tank Sensor Reading Below Normal |
| FMI 4 | Air pressure sensor circuit, circuit 4, shorted to ground |
| FMI 5 | Air pressure sensor circuit, circuit 4, open |
| FMI 7 | Air pressure sensor signal, circuit 4, out of range |
| FMI 9 | J1939 AIR1 Message (Air Supply Pressure) is missing from first source address |
| FMI 13 | J1939 AIR1 Message (Air Supply Pressure) is missing from second source address |
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.