Safe to driveDrivable, but watch it yourself
J1939 code SPN 1623. Below — how the fault is worded at the factory by Mercedes-Benz and SITRAK, and what the second half of the code (FMI) means in the standard.
| FMI 9 | Tachograph Output Shaft Speed - Abnormal Update Rate |
| FMI 13 | J1939 Tachograph Output Shaft Speed Signal is missing or not available = SNA (signal not available) |
| FMI 3 | Engine speed output short to battery. Scan tool code: P100C. Effect: Torque may be limited. |
| FMI 4 | Engine speed output short to ground. Scan tool code: P100D. Effect: Torque may be limited. |
| FMI 5 | Open load in the engine speed output circuit. Scan tool code: P100A. Effect: Torque may be limited. |
| FMI 6 | Over-temperature of the engine speed output powerstage. Scan tool code: P100B. Effect: Torque limited, the engine may shut down. |
| FMI 12 | Timeout of the TCO1 CAN frame. Effect: Loss of communication with the modules, some functions are disabled. |
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.