Do not driveTo the nearest safe stop
J1939 code SPN 28. 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 Temperature and Level Sensor Communication Interruption. FODP code (scan tool): U02A2-00. |
| FMI 8 | Transmission retarder torque signal fault. Repair: Run the diagnostic check of the intarder electronic unit. Check the Astronic unit 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: "driveline retarder — actual percent torque". |
| SPN 28 FMI 028/0 · 28.0 | data above normal range (most severe level) |
| SPN 28 FMI 828/8 · 28.8 | abnormal frequency or pulse width |
Do not drive. Stop as soon as it’s safe to do so — don’t keep going.
The code is flagged critical: the manufacturer considers it unsafe to keep driving without checking.
This code alone cannot say what will fail next, so stop at the first safe opportunity and look at it on the spot.
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.