Production of a second group of locomotives is on hold as a Chinese manufacturer tries to eliminate serious problems KiwiRail has had with its first order from the firm.
A KiwiRail document obtained by the Labour Party reveals a large list of issues the 20 locomotives have experienced since coming into service in the past two years.
The DL locomotives were bought from CNR Dalian Locomotive and Rolling Stock Company for $75 million.
Since they were introduced into service there have been various problems with the control system, traction motor, water pipes, exciter base, vibration, silencer, compressor auxiliary, basin pump, adhesion and with other equipment.
The trains are currently failing about twice as often as other locomotives in the fleet.
KiwiRail chief executive Jim Quinn says problems are part of the commissioning process and repairs will be completed by September.
"Every locomotive we've had over the years has had commissioning issues," he says.
He says the DL locomotives are the first of their kind, and takes a while to bed them in.
Another 20 locomotives, purchased for $62 million, were due to begin arriving this year, but Mr Quinn says production is on hold while they make sure the prototype is exactly right.
Each locomotive will spend one to three weeks in the workshop under the rectification programme. Eighteen staff from manufacturer CNR are in Hamilton assisting KiwiRail.
Rail and Maritime Transport Union general secretary Wayne Butson says the level of failures and problems is unprecedented and goes well beyond commissioning issues.
He says KiwiRail has admitted to the union it does not have any records from past commissioning processes to refer to, so it is misleading for it to say the Chinese locomotives are on a par with other locomotives.
Labour Party leader David Shearer says the decision to go for the cheapest option could prove expensive in the long run.
KiwiRail says it is happy with the quality of the locomotives and there will be fewer commissioning issues with the second generation.
The state-owned enterprise says it has not lost any revenue due to the problems, and parts and labour are also covered under warranty.