A tour bus driver has told police that he warned his company three days ago that his vehicle was not roadworthy.
He said it should not be used to transport tourists until it was repaired.
He claimed that nevertheless, the company ordered him to take the Chinese tourists back to Bangkok.
Thirteen of the 17 passengers on board were taken to hospital in Pattaya after the vehicle veered off the road on Route 7 KM marker 120 and hit a barrier and lamppost.
Driver Kiatchai, 38, said he had been driving the tourists around in Pattaya for three days and had warned the company, something that fell on deaf ears, he claimed.
He said there was a problem with the bearings in the steering column that caused him to lose control.
The company is based in Phrapradaeng.
Their website in English and Thai has a section on safety itemizing the existence of six fire extinguishers, four hammers, seatbelts for all, stickers warning of hazards, GPS and automatic door sensors.
There is no mention of maintenance in the safety section.
Police are investigating.