Safe to driveTo the nearest safe stop
J1939 code SPN 31. Below — how the fault is worded at the factory by Ford Trucks, Renault Trucks and ZF AS-Tronic, and what the second half of the code (FMI) means in the standard.
Ford TrucksRenault TrucksZF AS-Tronic
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 0 | Urea Level Sensor Electrical – Chassis Short Circuit. FODP code (scan tool): P203C-00. |
| FMI 8 | Engine retarder torque signal fault. Repair: Run the diagnostic check of the EECU electronic unit. Check the parameters. Switch the ignition off, switch it on again and repeat the test. If the fault persists, replace the control unit. |
ZF AS-Tronic uses its own fault numbering: the number in the table below is an internal ZF code, not a J1939 SPN. It matches the title of this page by digit only and means something different.
| FMI 8 | No CAN bus signal: "engine retarder — actual percent torque". |
| SPN 31 FMI 031/0 · 31.0 | data above normal range (most severe level) |
| SPN 31 FMI 831/8 · 31.8 | abnormal frequency or pulse width |
Safe to drive. Below — how much time you have and what happens if you keep going.
The gearbox or clutch has gone into limp mode: some gears may be unavailable and an automated box may stop shifting under load.
The main risk is being left on a climb with no gear and rolling back. Do not take a loaded truck into the hills; reaching level ground and a shop is fine.
That said, the manufacturer flags this code as critical — if in doubt, it is safer to stop and check on the spot.
Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.