A report by the Motor Trade Association (MTA) based on NZ Transport Agency data showed Otago, along with Waikato and Gisborne, had the highest fail rates in New Zealand at 46%.
Southland was not far behind at 45%, while the national average was climbing and stood at 41%.
City Mechanical Repairs manager Tony Crowther said he was not surprised at Otago's high failure rate.
He said it was because there were more older cars on the road and mechanics in the region were more scrupulous in their inspections.
He had seen "scary stuff", such as completely worn-out tyres.
Dunedin's hills also resulted in more brake and clutch failures, because drivers tended to brake more often and clutches in older automatic cars were often not equipped to deal with steep terrain.
The change from six-monthly to yearly warrant of fitness testing for cars registered after the year 2000 was also contributing to a higher fail rate across New Zealand.
Tyres and brakes seemed to be the most likely culprits behind warrant failures.
However, with more older cars in the region, rust problems were also common.
Nationally, official figures showed the number of cars failing at their first presentation for a Wof had climbed steadily in the five years since annual checks superseded six-monthly ones for most light vehicles.
It has gone from 34% of all inspections in 2014, to 41% now, a rise that represents more than a quarter of a million vehicles.
The Government's new Road to Zero proposals that aim to reverse the rising road toll include a review of how cars get warrants of fitness.
However, the biggest Wof issuer in the country, VTNZ, and the Motor Trade Association (MTA) which covers thousands of inspectors, both point to big information gaps in the vehicle defect and crash data the policymakers are relying on.
"We've seen a trend of increasing warrant of fitness fails and vehicle factors contributing to fatal crashes," Greig Epps, of the MTA, said.
"If we can't analyse the data, if we don't have the data to analyse, we can't figure out what to do next and how to fix the problem."
Wof consultant Andrea Andrews, who gives advice to 200 garages nationwide, said there needed to be a return to six-monthly warrant of fitness checks.
- Additional reporting RNZ
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Comments
People are not maintaining their vehicles the sake of their own conscience and assurance while driving , but to a lesser degree are maintaining them to keep central government departments happy.
"older cars contribute to high warrant failure rate" Like everybody has the money to buy a new car.