TC reported TIMS shows obstacle detectedat Rear DT car B4 door. Staff(KRJ) checked and confirmed no obstacle/object caught in between the doors. No other abnor malities. ~~~~~ 3656 TC reported TIMS shows obstacle detected at B4 door. Staff(KRJ) confirmed no obstacle/object caught in between the doors. No other abnormalities. CE: T210 - 3656 B4 Door no Obstacle detected. Door Operation ok OE request for depot to check.  3656 B4 door checked/found no FOD. Postulate FOD dislodged. Cleaned J-rail & checked rollers - OK. Swapped #3656 B4 DCP (1512W020021S036) with #1656 B1 DCP (1512W020021S019). Door cyclic test 20x, no DIR fault occurred.  Alan/Sugu/Lee PT 44801