VOBC passive / Speed sensor failureDT3556 encountered the above symptom. LDC log analysis show: Large discrepancy between velocity. RS event record show BCP abnormalities at 3556. Please investigate and follow up, thanks. Train cleared on Signal side. ** Fault timing: ADM2, 0852hrs. ~~~~~ 3556 VOBC passive / Speed sensor failure DT3556 encountered the above symptom. LDC log analysis show: Large discrepancy between velocity. RS event record show BCP abnormalities at 3556. Please investigate and follow up, thanks. Train cleared on Signal.  3556 replaced with new BCU. Checked tacho resistance within specs. Swapped #2556 BCU to #1555 & adjusted the wheel diameter accordingly. Checked BCP - OK (BCP checklist attached).  Shafie/Sugu/Lee PT 44641