SRT Electrified Train, which operates the Airport Rail Link (ARL), has been ordered to find the party responsible for the shambolic rescue operation which took place after one of its trains broke down on Monday, stranding hundreds of passengers in hot carriages.
Deputy Transport Minister Ormsin Chivapruck said Tuesday he had instructed the company to find out who should be held accountable.
He added ARL management will be penalised for failing to properly maintain the system, which led to the break-down.
A power failure halted the train and trapped more than 700 passengers in stuffy carriages without air conditioning for an hour en route from Suvarnabhumi airport to the city on Monday morning.
Prime Minister Prayut Chan-o-cha said SRT Electrified Train, a subsidiary of the State Railway of Thailand, must be investigated for leaving its emergency backup power system out of order for months.
"I have checked. The airport link has had problems for a long time. No one has bothered to pay attention," Gen Prayut said.
He said the ARL trains would be modified to carry more passengers, and the company would not buy additional trains at this time.
The six-year-old ARL route stretches about 29 kilometres from inner Bangkok to Suvarnabhumi airport, east of the capital.
Mr Ormsin said the company had failed to maintain the rail system and take sufficient care of commuters.
The deputy minister said he expected the purchase of new emergency power backup units for seven stations, at a cost of 32 million baht, would be approved by the SRT board by next Tuesday.
He said Gen Daran Yuthawongsuk, the director and acting president of the company, had been aware of the decrepit emergency backup power system since October last year, but failed to fix the problem even though he had the authority and money to do so.
Mr Ormsin said the SRT board had allocated the company 380 million baht for an overhaul of the system, but management opted for a partial overhaul.
Each ARL train requires a major overhaul after it has run 1.2 million kilometres.
However, the trains have each clocked up between 1.5-1.6 million km.
Gen Daran admitted Tuesday staff must improve how they deal with passenger rescues.
They should have opened the train doors for stranded passengers to allow air to circulate and advised them to remain on board.
The rescue was hampered by some passengers who managed to escape from their carriages and who descended onto the rail tracks, which prevented the train from being towed to the station quickly and added to the delays.