Sheffield Supertram services are facing severe delays and route alterations due to a points failure – just two days before the tram-train scheme is due to launch.
Stagecoach, which operates the service, said purple route services were being affected by a points failure at Sheffield Cathedral.
The firm said services from Herdings Park will run to Shalesmoor via Cathedral, where they will tun back and return to Herdings Park.
Passengers have been warned to expect delays.
The long-awaited Sheffield to Rotherham tram train will finally welcome passengers on Thursday – almost three years late and at five times the original budget.
The service, which will see tram trains run from Sheffield ot Parkgate Shopping via Rotherham Central railway station, will launch on Ocotber 25.
The first service will leave Cathedral tram stop at 9.39am, arriving at Parkgate at 10.09am.
Three services will operate an hour and will travel on the Supertram network from Sheffield Cathedral to Meadowhall South / Tinsley, before proceeding over a new section of track linking the tram line to the rail line.
It will then continue on to the national rail network to Rotherham Parkgate via Rotherham Central station.
Journey times between Sheffield Cathedral and Rotherham Parkgate will be 27 minutes.