The truck and BP tanker trailer decoupled on the Wodonga-Yackandandah Road on August 7, 2014.

The trailer hit two vehicles, with three people killed.

The prosecution alleges Heavy Mechanics failed to ensure people weren't exposed to risks and failed to properly service the coupling between the truck and trailer.

The company's director Keith Haire gave evidence in an earlier trial, which was replayed to the jury in the Wodonga County Court on Tuesday.

He said one type of service undertaken by the business was "a very quick service just to make sure the vehicle's not falling apart or anything like that".

He said there was "absolutely no movement" in the coupling, which meant he knew a nut was tight.

The court had heard the nut was key to the towing system.

Wear would allegedly be caused to components unless the system was completely rigid.

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It's alleged the company should have decoupled the truck and trailer during services to check for movement.

Mr Haire said nothing he saw indicated a need to disassemble the coupling and no damage was viewed.

Lawyer Daniel Gurvich QC asked if it wasn't industry practice to disassemble a coupling during a service.

"You do not pull it apart," Mr Haire said, and said a lack of movement meant the nut was tight.

Mechanic Richard Trethowan, who conducted the final service six days before the crash, said the tow eye coupling "was all good".

He said the business was highly regarded and his boss "extremely thorough in my books".

Materials engineer David Padfield tested the failed components.

He also told the court there shouldn't be any movement.

"There shouldn't be any wiggle room between the tow components, so they should, once inserted, it should be quite almost stiff in a way," he said.

Mr Padfield said movement, even if small, would cause damage.

The trial will continue on Wednesday.

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