An engineer who inspected a truck after it smashed into a campervan, killing two Spanish tourists, says there was no evidence of any major mechanical faults.
Joan Roma-Serra and Eva Fajula-Rovira, who were both 34, died at the scene of the crash on State Highway One, north of Whangārei, in 2009.
The first coronial inquiry in 2012 found driver error caused the crash.
A second inquest is being held in Auckland, after the driver of the truck asked the Solicitor-General for the case to be reopened in 2016.
The truck driver, Ioane Etuale, has told the hearing a power steering failure was the cause.
Mr Etuale said he heard a loud snap before the crash, and lost the ability to steer the Linfox vehicle.
But an engineer who inspected the truck after the accident, Dennis Smith, said what he found did not back up that claim.
Mr Smith was asked by lawyers representing Linfox to provide a report on the truck in its damaged condition.
He told the inquest he couldn't identify any mechanical faults with the truck's steering system.
The steering was used to move the truck around the yard at Truck City and while the power steering was not operational due to damaged hoses, the truck could be maneuvered normally.
The steering box was tested and then dismantled for further inspection, Mr Smith said.
"No fault was found in the steering box ... there were no faults found on any other steering components."
Trucks did not require power steering at high speeds and typically only used it at lower speeds, Mr Smith said.
A truck driver wouldn't necessarily even notice if power steering had failed at a high speed, he added.
A total loss of power steering was inconsistent with a steering wheel becoming loose and a driver losing control, Mr Smith said.
Mr Etuale told the inquest oil on the road after the crash clearly showed there was a mechanical fault.
But Coroner Peter Ryan said photos of the crash did not appear to back up that claim.
Police and the fire brigade washed away the oil before the pictures were taken, Mr Etuale said.
He claimed they did this to cover up that they had ignored previous warnings about the quality of the road.
When asked about the oil, Mr Smith said if the truck had lost oil, its reservoir would be the first indication that was the case.
It was full upon inspection, he said.
Coroner Ryan asked if Mr Smith could think of anything that could have caused the total loss of steering Mr Etuale had earlier described.
"The only thing I can possibly identify is this tyre failure and loss of pressure in a tyre."
Mr Smith earlier told the inquest about a slow leak he had identified in one of the tyres.
When the truck had arrived for its inspection after the crash the tyre was fully inflated, he said, but a few days later it was completely deflated.
"Other than mechanical failures, if the axles were dislodged, or if the trailer become unstable at the back, I have no information on what the condition of the trailer was but that could have an effect if it were to provide a severe side-loading unexpectedly.
"I assume the police would have carried out inspections of the trailer, or any damage in that area, or non-compliance."