Do not driveTo the nearest safe stop
J1939 code SPN 1656. Below — how the fault is worded at the factory by Ford Trucks, and what the second half of the code (FMI) means in the standard.
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 | Input Nox Sensor (1) Communication Interruption. FODP code (scan tool): U029D-00. |
| FMI 1 | Output Nox Sensor (2) Communication Interruption. FODP code (scan tool): U029E-00. |
| SPN 1656 FMI 01656/0 · 1656.0 | data above normal range (most severe level) |
| SPN 1656 FMI 11656/1 · 1656.1 | data below normal range (most severe level) |
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.