ScotRail has today taken its brand new fleet of electric trains out of service as a "precaution" over defective brakes, The Scotsman can reveal.
The move caused a shortage of carriages on dozens of trains on the main Edinburgh-Glasgow line and other routes today.
It was triggered by one of the class 385 trains suffering a brake fault on the line at Winchburgh yesterday, which blocked the line and caused significant disruption.
ScotRail admitted it was the latest of a series of similar problems to have hit the trains since last month - just two months after being introduced.
Six of the fleet of 70 Japanese-designed Hitachi trains have been running on the line and on the North Berwick-Edinburgh route.
ScotRail said some of its services had fewer carriages than normal on the main Edinburgh-Glasgow line via Falkirk High route this morning as a result.
More than 30 trains on the route will run with a reduced number of coaches today, including some cut from seven to three.
Many trains on North Berwick line ran with just three carriages - half the normal number.
A rail source said of a previous incident last month: “The train almost overshot Falkirk High, due to ‘very poor brakes’ after investigation by Hitachi.
“In the rear three carriages, a computer isolated all the brakes for no apparent reason, so only the front four carriages were braking.”
ScotRail and Hitachi have provided no details of the incidents.
The train operator said: "Hitachi is investigating the cause of the technical fault, but there is nothing to suggest it was a software problem."
However, it denied it related to slippery tracks caused by leaves.
ScotRail chief operating officer Angus Thom said the trains had been taken out of passenger service while the fault was investigated.
He said: “As a precaution, while Hitachi carries out further testing, we are restricting the use of class 385 trains.
“We are sorry to any customers whose journey was disrupted as a result of this.”
A ScotRail spokesman said last night: “The train in question today is heading to [Edinburgh depot] Craigentinny for testing.
“It caused some delays and cancellations earlier in the day.
“There were a small number of cancellations in September caused by the fault.
“All trains have normal braking and secondary braking to keep people safe.”
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The first train in the fleet entered service in July, ten months late, after a series of problems including the driver's windscreen, which had to replaced because it distorted the view of signals at night.
There were also delays to the electrification of the main Edinburgh-Glasgow line.
The setback follows ScotRail admitting that another fleet of trains being drafted in to provide more seats on inter-city routes such as Aberdeen-Edinburgh will be introduced later this month without being refurbished because of problems at refitting firm Wabtec.
Scottish Liberal Democrat transport spokesperson Mike Rumbles said: “This is yet another let down for Scotland’s rail users.
"Commuters will be dismayed to see the first trains from the new Hitachi fleet, introduced with great fanfare just weeks ago, taken out of action.
“The trains we have already are over-packed, the long-distance trains promised are running late and are set to come into action without being refurbished first, and now the new trains have been taken off the rails too.
"It’s a bleak outlook.
“Passengers just want trains to be reliable and value for money but they are getting neither.
The transport secretary [Michael Matheson] needs to get to grips with the catalogue of errors that hold up our rail network and get ScotRail back on track.”
Scottish Labour transport spokesman Colin Smyth said: "While it is important these defects were identified and dealt with quickly, this is another blow for passengers under this franchise.
"The SNP promised a world-leading service with ScotRail.
"Instead we have seen the problems pile up with trains withdrawn, new models late, services overcrowded, overpriced and routinely behind schedule."
David Sidebottom passenger director of passenger watchdog Transport Focus said: “Passengers will be disappointed to hear this error occurred and want assurances from ScotRail that there is a clear timescale for these trains to be back in service.
"Only then will people feel confident that they are getting the best value fare and a reliable service."
A spokeswoman for the Scottish Government's Transport Scotland agency, which controls the ScotRail franchise, said: "ScotRail has made us aware a technical issue was encountered on one of the new class 385s yesterday.
"As is normal in such circumstances, particularly with new trains, Hitachi will test the entire c385 fleet as a precaution to ensure reliable operation.
"It is imperative this testing is completed quickly, but thoroughly, to ensure the c385s can get back into service as soon as possible."