Test runs of new railcars delivered to Iarnród Éireann as part of a multimillion-euro order have been delayed because of mechanical problems.
Gearbox transmission difficulties emerged in the first train delivered by the Spanish group CAF, which arrived in January, two months after a scheduled delivery date in November.
The train has been stationed at the Iarnród Éireann depot in Inchicore, Dublin, since then, pending repairs.
Test runs will not begin until the middle of March after the delivery next week of the first modified train. Each of the trains under construction has had to be modified at CAF's plant in Beasain, near San Sebastian.
Iarnród Éireann has ordered 20 trains from CAF, each train comprising four carriages, at a cost of €115 million, and an additional 67 mainline carriages at a cost of €117 million. The suburban trains will be mainly used on routes linking Dundalk, Kildare and Arklow with Dublin.
A testing programme which usually takes about six months has been delayed because of a gearbox fault. It was expected to begin at the start of this month on the stretch of line between Limerick Junction and Mallow.
Most of the tests will be carried out at night, to avoid disruption to timetables.
Confirming that a fault had emerged, an Iarnród Éireann spokesman said: "The responsibility is the manufacturer's and there is no added cost to us."
Despite the delay, the company is still confident that the first of the new trains can go into service during June, as planned.
Iarnród Éireann normally brings out a new annual timetable in May or June of each year. However, a six-month timetable will be introduced for the June-December period, when the new trains are commissioned.
Another new timetable will be introduced next January as more of the trains come into service.
Each of the trains has the capacity to carry about 750 people. Their introduction is expected to increase capacity on suburban routes.
It is planned to run a double set of the trains, with eight carriages, on some routes.