The latest delay follows extensive safety checks by Centro, the delivery arm of the West Midlands Integrated Transport Authority, on the eve of the planned opening.
Centro’s Midland Metro programme director Phil Hewitt said: “It is bitterly disappointing as everything else is in place and ready to go but, as we have said right from the start, safety is paramount.
“A stringent testing programme has identified minor anomalies in some of the track alignment which need to be addressed.
“These are exactly the sort of issues the tests were designed to identify.
“However remedial work is relatively straightforward. Once that is complete, on-street driver training can begin and we will soon have passenger services running.”
Balfour Beatty won the £127m contract to deliver the 1.2km extension from Snow Hill to New Street back in August 2013 .
At the time the 1.2km Midland Metro extension through Birmingham city centre was programmed to finish late last year.
This had to be put back to May due to technical issues caused by difficulties associated with existing utilites during construction.
Trams returned to the streets of Birmingham for the first time in more than 60 years last December when the Metro started running to the new stop in Bull Street.