The Greater Wellington regional council hopes to have the first of its new Matangi trains in service by the end of the week.
The council has purchased 48 of the Korean-made two-car units as part of the $550 million upgrade of the network.
The council says the first train was meant to be operational in late February but is now expected to be running on Friday.
The council says completing all the necessary paperwork has delayed the service, not glitches.
It could not confirm whether a further two trains would be in service by the end of March.