Reported 3566 with recurring BCU WSP fau ~~~~~ 2566 Reported with recurring BCU WSP fault on both bogies since August 20.  2566 ER D/L & found the following frequent FC : FC 327 - BCU Speed Probe 4 Fault FC 322 - BCU WSP Timer 1 Activated FC 323 - BCU WSP Timer 2 Activated. Analysed ER & found WSP occurance only on #3566 at fault recorded timing. Physically checked dump v/v 1 & 2, wheels for any defects & BCU cannon plugs security - All OK. On exterior outlook of BCU confirmed recent c/o to GEN 2.1. Further checked TachoGen 4 & found impedence fluctuating. Replaced Tacho 4 on 3566. Limited movement & fault not duplicated. To further monitor during M/L revenue service. 3566 Tacho 4 S/N : OLD : 1249223 NEW : 1015109  Kana 44097