Do not driveTo the nearest safe stop
J1939 code SPN 21. 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 Injector Inconsistent Operation. FODP code (scan tool): P208E-00. |
| FMI 1 | Urea Dosing System – Pump Inconsistent. FODP code (scan tool): P208B-00. |
| FMI 2 | Active emergency braking system electrically – not connected. FODP code (scan tool): U101C-02. |
| FMI 5 | Short to 0 V. Repair: Check the wiring between the control unit and the clutch actuator. Run the diagnostic check of the clutch actuator. 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 5 | Short circuit to ground on valve Y14 output (clutch fast engagement). |
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.