Train doors at Rear DT 'B1' door were not proven closed. Staff(GCL) checked and confirmed that Rear DT 'B1' door had a small gap, unable to close. Staff(GCL) as sisted to isolate the defective pair of train doors for trai ~~~~~ Confirmed 3623 B1 door isolated. From TIMS retrieve fault code 933. Fault unable to duplicate in depot. Fault trace downloaded. Checked door force and observed measurement as follows; LHS: 6.5kgf and RHS: 3.5kgf. Removed door leaves to check door rollers - satis. Cleaned door guide rails. Reinstate door leaves on 3623 B1 door and checked new force for both door leave at 3kgf. Function test door ok. conduct train doors open/close 20 times - satis with no fault occurred. Request for CE to monitor during mainline. N.A/kumar/azli/nazrul/07.12.22