1509 Train prep reported BCU fault. ~~~~~ #1509 FC 308/330/331 Brake cyclic test check ACU no sign of abnormalities.Check PBSV & Brake silencer no sign of leak.Physical check brake able to release and apply,brake status ok.BC1 isolated <1min air stop purging.Isolated BC2 <1min air stop purging.#1509 ACU swap to #2509 conduct brake cyclic ok.Unoccupped cab for 10min.Occuppied CAB BACK FAULT TRANSFER TO #2509.sAME FAULT CODE 308/330/331.Replace #2509 ACU and brake cyclic test ok.BCP within criteria. #2509 ACU:- Old s/n: 1047-079    New s/n: 1047-085 Not: 2431869 raise to CSC. Done by Saini/Haslan. 02/11/22