Safe to driveTo the nearest safe stop
J1939 code SPN 191. Below — how the fault is worded at the factory by Mercedes-Benz, Renault Trucks and ZF AS-Tronic, and what the second half of the code (FMI) means in the standard.
Mercedes-BenzRenault TrucksZF AS-Tronic
| FMI 9 | J1939 ETC1 Message is missing or not available |
| FMI 13 | J1939 Transmission Output Shaft Speed Signal is missing or not available = SNA (signal not available) |
| FMI 19 | J1939 Transmission Output Shaft Speed Signal erractic = undefined value but not SNA |
| FMI 0 | Checksum fault. Repair: Perform the programming. |
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 0 | EEPROM programming parameter checksum error. |
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.