Train doors at Rear M1 car were not proven closed. TC recycled train doors a few times but to no ava il. Staff(JUR) feedback had isolated train door at Rear M1 car 'A3' door in closed position but DIR indication remained. ~~~~~ 1651 Train doors at were not proven closed. L3 TC recycled train doors a few times but to no avail. Staff(JUR) feedback had isolated train door at Rear M1 car 'A3' door in closed position but DIR indication remained. L3 1651 A3 door FC CLE, NRD, DOM. # #1651 A3 door found Door Lock Switch not energised when door physically closed. ER showed DIR unable to energise when doors commanded to close. TC cycled multiple times the wrong side of door & unable to clear fault. DIRBS activated to return to depot. Replaced Door Lock Device on #1651 A3 door. Function test ok. Also replaced manual isolation lock due to defects.  Jonathan Koh 45257