All but three (B121, B125, and B135) were fitted with Train Door Control equipment for operation with the Inchicore-built, BR Mark 3 based, Push-Pull train units. The push-pull equipment of locomotive B132 was subsequently decommissioned. Entering service in 1989, these trains, consisting of a single 121 Class and up to six carriages, were mainly used on the Dublin northern suburban passenger railway service. These were to be the last regular passenger duties for the 121s within Greater Dublin. The Limerick shuttle continued to be worked by 121s for several years after this date. In 1994, a railcar "revolution" had begun, and the push pull carriages were later re-deployed to inter-city duties with the 201 Class locomotives.