Safe to driveDrivable, but watch it yourself
J1939 code SPN 178. Below — how the fault is worded at the factory by ZF AS-Tronic, and what the second half of the code (FMI) means in the standard.
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 4 | CAN bus fault. |
| SPN 178 FMI 4178/4 · 178.4 | voltage below normal or shorted to ground |
Safe to drive. Below — how much time you have and what happens if you keep going.
This is an electrical fault: an open, a short or a bad contact in the sensor circuit. The value it measures is most likely fine.
You can drive. But until the circuit is repaired this system runs blind and cannot warn you about a real failure.
Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.