A mechanical problem is causing Caltrain delays Monday morning.
The problem occurred on northbound train No. 221, which was taken out of service at the Millbrae station, Caltrain spokeswoman Christine Dunn said.
Passengers aboard that train were able to transfer to the next northbound train.
As of 9 a.m., three northbound trains were behind schedule by up to half an hour.
There were no delays to southbound trains.