Train door not proven closed at Rear M1car. TC opened and closed a few times to no avail. Staff(BBT ) checked and confirmed Rear M1 car 'B4' door not proven clo sed. Staff(BBT) isolated Rear M1 car 'B4' train door in clos ~~~~~ Train door not proven closed at Rear M1 L3  No door related FC during fault timing    Open Close speed pass: Yes FOD found: No Door cycle 20x: Yes Rubbing marks: No Door Push/Pull force: Satis Door mating gap: Satis Door Lock Switch red line when door closed ok. Door Lock Switch Cushion Rubber intact: Yes Door Close Switch distance from actuating plate within criteria. Door Wobble: No Rectification Actions: When 1701 B4 doors were normalised, doors were able to cycle without any abnormalities. There was a scratch mark along the guide rail of 1701 B4 door. Postulate FOD caused the door to be stuck, and subsequently dislodged when staff pushed the door closed and train returned to depot. Checked door operation, found to be smooth. Checked guide rail and J-rail satis. No signs of wobbly door. Preventively changed out the Door Lock Device as there was no FC during time of fault. Checked both sides DIRBS sealed. Done by: Sanip, Koh, Jack (5/6/24)