TIMS showed Fire / Smoke Internal at car3551. Staff(TWR) checked and confirmed no signs of smoke / fire / burning smell on exterior or interior of train. ~~~~~ TIMS shows FC 720 - Smoke internal occurred once resettable Fault unable to duplicate in depot Blow clean 3551 both ends smoke detector Found no.2 end smoke sensor unit very dusty, preventively replaced sensor Both sensor units cannot plug checked, no water ingress or oxidation No fault occurrence during monitoring N.A /SANKAR/FAIRUZ/AZLI/20.08.23