TIMS showed Smoke External Alarm at car2555. Staff(AMK) checked and confirmed no signs of smoke / f ire / burning smell on exterior or interior of train. Rear T 405 line clear and confirmed no abnormalities. TIMS showed S ~~~~~ 2555 TIMS showed Smoke External Alarm. Staff(AMK) confirmed no signs of smoke/fire/burning smell on exterior or interior of train. Rear T405 line clear and confirmed no abnormalities. IMDC(RS) was informed. Train was scheduled withdrawal to UPD after morning peak CBR NB.  2555 FC 721/731. Checked smoke detector external cable gland - OK. Found rubber gasket missing at Terminal cover. Cleaned smoke detector as preventive measure. Swapped SDR-11 from #2555 to #2556 for monitoring. OPS 20 raised to BSD to c/o smoke detector at #2555 NO.2 End.  Anand/Sugu 45154 2555 To C/O External smoke detector.   Checked and found smoke external sensor to be very dusty and PCB having slight corrosion. Replaced and function test ok. Notification to CSC: 2518601 Done by: Rizman, Shah (26.8.2023)