Safe to driveDrivable, but watch it yourself
J1939 code SPN 623. Below — how the fault is worded at the factory by International, and what the second half of the code (FMI) means in the standard.
| FMI 4 | Red Stop Lamp |
| FMI 5 | Red Stop Lamp — Red stop light malfunction; Red Stop Lamp |
| FMI 6 | Red Stop Lamp |
| SPN 623 FMI 4623/4 · 623.4 | voltage below normal or shorted to ground |
| SPN 623 FMI 5623/5 · 623.5 | current below normal or open circuit |
| SPN 623 FMI 6623/6 · 623.6 | 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.