Two services are affected by the fault, which is on the line between Carluke and Lanark.
Services from Lanark to Dalmuir and Milngavie to Motherwell have been delayed.
Scotrail posted a notice on it's website this morning.
It said: "Owing to signalling problems between Carluke and Lanark: Train services running to and from these stations may be cancelled, delayed by up to 15 mins or revised at short notice.
"Disruption is expected until 9.15am.".
Signalling problems at Ladybank are also causing delays for passengers travelling through the station from Glasgow to Edinburgh and Inverness.