About two thirds of vehicles inspected after New Zealand Transport Agency alerts of faulty tests have failed their new Warrants of Fitness.

Photo: 123RF

Out of 741 vehicles re-checked, 465 failed and needed repairs in order to pass.

This leaves another 19,000 vehicles still to be seen, and the slow rate drivers are responding to the New Zealand Transport Agency's (NZTA) warning letters suggests there will be a significant delay before they are re-tested.

In Dargaville, where the alerts went out in September, only a third of the 2000 alerted owners had their cars rechecked.

This has forced the agency to extend the life of the re-inspection vouchers for these owners by two months, until Christmas Eve. Others have until February.

One young driver, who RNZ agreed not to name, chose to use one of the Auckland garages that is now suspended for the very reason it would pass his 20-year-old car. About six of his friends had done the same.

"I was driving on the motorway in December 2017 and was involved in a crash that I believe could have been prevented if my brakes had been checked properly because I had known for a number of months after I got my [WOF] test that my brakes were soft and that I wasn't stopping as quick."

He rear-ended another car at about 60kmh. He got whiplash but no one else was hurt.

"This place was well-known amongst my friend group as someone you could go to and get a warrant of fitness done that was dodgy.

"We're probably all a little disappointed in ourselves for taking advantage of that but, as I say, back when I was a bit younger, the main priority was money, not safety."

He and his friends were now rethinking their preference for easy warrants dished out at for as little as $27 each, taking just 20-30 minutes.

In Coromandel township, Jessica and Mark Henson count themselves lucky to have come off with damage to just their pockets and trust in the WOF system.

They bought a 1969 Ford XW two years ago.

"We assumed that with a brand-new warrant everything on it was tickety boo," Mr Henson, a 45-year-old builder, said.

"Six months down the track and driving around with our kids in the car, we found that it failed major structural rust and was really dangerous to drive."

Rust was in the pillars, sills and boot, according to emails RNZ has seen.

The Hensons spent almost $10,000 on repairs.

There was no recourse to the Ōtāhuhu garage that had warranted it: Chester Brown Motors had been sold and its inspector was gone. RNZ has been unable to contact him.

NZTA told the Hensons, in emails provided to RNZ, that this rendered it powerless.

"The vehicle inspector who issued the WOF to your vehicle on 14th December 2016 is also no longer issuing WOFs. Therefore, we wouldn't be able to conduct an investigation from our end into whether or not the WOFs should have been issued," the agency's complaints adviser said.

The Disputes' Tribunal told them there was no way they would win a case against the previous owner because NZTA was at fault.

VTNZ is disputing a shuttle company's claims that its Gore testing site passed a bus when it should not have.

Waiheke Shuttles bought the bus second-hand in Balclutha with a fresh Certificate of Fitness (COF).

On return to Waiheke it was put through another COF test and the company said it was "alarmed that it failed several items".

"The repairs to the bus cost several thousand dollars."

The Vehicle Inspection Requirements Manual, or VIRM, which all inspectors sign up to, is meant to eliminate big variations between testers.

The shuttle company complained to both the NZTA and VTNZ.

VTNZ general manager of operations Greg O'Connor said in a statement that they were investigating but they believed the issues were not present at the time of the first inspection.

"Many of the items raised could have occurred during the 1600 kilometre trip when the bus was driven from Gore to Waiheke Island, others may have been undetectable during the COF inspection."