Four more car models have been added to the list of vehicles deemed too risky to warrant a discounted registration, which has affected thousands of motorists who missed out on cheaper car registration.
ACC has admitted overcharging 8800 people and says it will fix the problem and start working back through other complaints to see if more motorists are affected, following a Fair Go investigation.
The list of cars deemed too risky to warrant a discounted registration has been updated from 18 to 22 vehicles by ACC.
Shirley Hewitt heard the ACC was cutting the registration fee on average by 41 per cent, but her 2008 Nissan Skyline missed out because ACC told her it was in the highest risk category for causing injury.
"I wasn't too fazed about the price of the actual rego, I was more worried about the fact that they said my car wasn't safe," she told Fair Go.
ACC told Ms Hewitt that it based its call on a huge database of crashes reported by police in Australia and New Zealand - five and a half million of them between 1987 and 2009.
When Fair Go investigated it discovered that ACC was basing Ms Hewitt's registration cost on crash reports from Skyline's at least 20 years older than hers.
That ignored numerous safety features that give her 2008 model car five stars in one crash
Prompted by Fair Go, ACC says they looked into why Ms Hewitt's 2008 model was .
"That was when we found we actually had this coding error," ACC's Sid Miller says. "Thank you Fair Go."
The technical issues relate to imported second-hand cars. ACC says it identified that some vehicles had been allocated to the wrong risk rating bands so a rule was put in to fix the error. However another programme overrode that but it wasn't picked up until some customers contacted ACC about their vehicle banding.
Mr Miller says the problem was caused by a glitch in ACC's software that put Ms Hewitt's car in the wrong risk category, along with many others.
"9000 people have been impacted by not having the right info and I apologise for that," he says.
Customers with queries can contact ACC on 0800 222 776.
ACC says 22 models are affected:
Alfa Romeo, Spider, 1995 & 2006-2009
Audi, 80/90, 1991-1996
Citroen, XM, 1989-1995
Ford, Mondeo, 2001-2006
Ford, Mustang/Shelby, 1994-1998
Hyundai, Accent/Excel, 2005-2010
Nissan, Bluebird, 1996-2008
Mitsubishi, Galant, 1996-2011
Nissan, Cima, 1991-1995 & 2001-2008
Nissan, Laurel, 1989-2002
Nissan, Silvia, 1993
Nissan, Skyline, 1993-2010
Nissan, Prairie/Liberty, 1988-2004
Suzuki, Alto, 2004-2011Renault, Scenic, 1997-2000
Suzuki, Carry, 1999-2006
Toyota, Corona, 1992-2002
Toyota, Supra, 1993-2002