Safe to driveDrivable, but watch it yourself
J1939 code SPN 645. Below — how the fault is worded at the factory by KAMAZ, Knorr-Bremse EBS, MAN, MAZ and YaMZ, and what the second half of the code (FMI) means in the standard.
KAMAZKnorr-Bremse EBSMANMAZYaMZ
| FMI 3 | Vehicle speed measurement, path 3 (pulse signal) |
| FMI 4 | Vehicle speed measurement, path 3 (pulse signal) |
| FMI 12 | Vehicle speed measurement, path 3 (pulse signal) |
| FMI 4 | Channel data connection with tachograph timeout. No signal |
| FMI 4 | Data connection with tachograph - No signal |
| FMI 3 | Vehicle speed sensor fault - Pulse width above maximum. Blink code: 3-2-4. Repair: Check the vehicle speed sensor and its wiring. Check the CAN bus connection. |
| FMI 4 | Vehicle speed sensor fault - Pulse width below minimum. Blink code: 3-2-4. Repair: Check the vehicle speed sensor and its wiring. Check the CAN bus connection. |
| FMI 12 | Vehicle speed sensor fault - Signal invalid. Blink code: 3-2-4. Repair: Check the vehicle speed sensor and its wiring. Check the CAN bus connection. |
| FMI 3 | Vehicle speed sensor fault (Pulse width greater than maximum). Blink code: 3-2-4. Repair: Check the vehicle speed sensor and its wiring. Check the CAN bus connection. |
| FMI 4 | Vehicle speed sensor fault (Pulse width less than minimum). Blink code: 3-2-4. Repair: Check the vehicle speed sensor and its wiring. Check the CAN bus connection. |
| FMI 12 | Vehicle speed sensor fault (Signal incorrect). Blink code: 3-2-4. Repair: Check the vehicle speed sensor and its wiring. Check the CAN bus connection. |
| SPN 645 FMI 3645/3 · 645.3 | voltage above normal or shorted high |
| SPN 645 FMI 4645/4 · 645.4 | voltage below normal or shorted to ground |
| SPN 645 FMI 12645/12 · 645.12 | faulty device or component |
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.