Train encountered BCU fault at Rear M2 car. Train was proceeding very slowly. TC performed brake sta tus check and fault subsequently self clear. Train was able to proceed in AM mode. TC also reported fault was intermitte ~~~~~ 2680 encountered BCU fault. Train was proceeding very slowly. TC performed brake status check and fault subsequently self-clear. Train was ableto proceed in AM mode. TC also reported fault was intermitted.  2680 found FC 308/312/314/330/331 & unasual ticking sound from ACU but no air leak found. Replaced ACU & function test - OK. Brake pressure test & no residual pressure at COAST - OK. No fault recurred. Limited/depot shunting - OK. 2680 ACU S/N :    OLD : 1541/191                   NEW : 1538/161 RF  : 1749/339                   RF  : 1749/564 (Mod 3) RC  : 1749/536                   RC  : 1749/003 (Mod 3) AF  : 1744/137                   AF  : 1847/972 (Mod 4) EM  : 1747/477                   EM  : 1751/405 (Mod 3) AC  : 1739/110                   AC  : 1851/231 (Mod 4) (Mod 3)  Sarma/Redzwan 43888