TIMS showed fire External Alarm at rearM2 car. Staff(AMK) checked and confirmed no signs of smoke /fire / burning smell on exterior or interior of train. Rear T442 line clear and confirmed no abnormalities. ~~~~~ 2515 TIMS showed fire External Alarm. Staff(AMK) confirmed no signs of smoke/fire/burning smell on exterior or interior of train. Rear T442 line clear and confirmed no abnormalities. CE : T430 - 2515 Smoke External pre-alarm fault. Reset. Fault Cleared.  2515 Found FC 721 (smoke external) on TIMS. Checked 2515 external smoke detector. Found smoke detector unit, plaseal, cable gland and gasket - OK. No water or dust ingress. Swapped SDR11 relay on fire control panel between #2515 & #1515.  Aliff/Redzwan 45174