Safe to driveDrivable, but watch it yourself
SPN 4056 is a manufacturer number outside the standard J1939 table: different makes can put different things under it. Below — how it is worded by International, Knorr-Bremse EBS and MAN, and what the second half of the code (FMI) means.
InternationalKnorr-Bremse EBSMAN
| FMI 5 | Two Speed Axle Actuator — Two Speed Axle Solenoid Relay Under Current Or Open Circuit |
| FMI 6 | Two Speed Axle Actuator — Two Speed Axle Solenoid Relay Short To Ground |
| FMI 3 | Central control unit, software error. Not identified |
| FMI 3 | Central control unit software error - Not identified |
| SPN 4056 FMI 34056/3 · 4056.3 | voltage above normal or shorted high |
| SPN 4056 FMI 54056/5 · 4056.5 | current below normal or open circuit |
| SPN 4056 FMI 64056/6 · 4056.6 | current above normal or grounded circuit |
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.