Safe to driveDrivable, but watch it yourself
SPN 3999 is a manufacturer number outside the standard J1939 table: different makes can put different things under it. Below — how it is worded by International, and what the second half of the code (FMI) means.
| FMI 5 | Electrical Load Shed ON — Load Shed ON Relay Under Current Or Open Circuit |
| FMI 6 | Electrical Load Shed ON — Load Shed ON Relay Over Current |
| SPN 3999 FMI 53999/5 · 3999.5 | current below normal or open circuit |
| SPN 3999 FMI 63999/6 · 3999.6 | 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.