TIMS showed Fire / Smoke Internal at car1639. Staff(KTB) checked and confirmed no signs of smoke / fire / burning smell on exterior or interior of train. Trainwas escorted to terminal station. ~~~~~ 1639 TIMS showed Fire/Smoke Internal. Staff(KTB) confirmed no signs of smoke/fire/ burning smell on exterior or interior of train. Train was escorted to terminal station.  1639 FC 720 (smoke internal). Checked no.1 and no.2 end smoke detector no signs of water ingress. Preventively swapped SDR1 from #1639 to #3639 and SDR2 from #1639 to #2639. OPS 20 raised to check internal smoke detectors.  Daniel/Redzwan 45373  Smoke internal sensor found dusty, clean up and function test-ok. Done by: Sanip and Koh