"Risks will increase if owners aren't vigilant."
Wairarapa road policing manager Sergeant Chris Megaw said car faults went "hand in hand" with irresponsible drivers, and were often a contributing factor to local crashes.
"We do come across a number a number of cars that aren't fit for the road," he said.
A green stickering system meant cars could be taken straight off the road, but while it was easy to spot a balding tyre, problems with brakes and steering weren't so simple to identify.
"We issue [green sticker orders] for vehicles that haven't had a warrant for many years."
All motorists should be checking the car before driving as responsibility fell on them - regardless of who owned the vehicle, Mr Megaw said.
Dunedin siblings Danielle Ngametua Kiriau, 17, and Shannon James Kiriau, 22, were both killed when their green-stickered Honda Integra, which should not have been on the road, crashed on May 17.
The car was not up to warrant of fitness standard.
Another fatal crash near Kopaki in Waikato last month - in which an unrestrained baby travelling on its mother's lap later died - is thought to have been partly caused by the condition of two bald tyres.
AA general manager of motoring affairs Mike Noon said the most important thing for drivers to check was tyre tread and air pressure.
"A lot of people have relied completely on their warrant of fitness but there are things that, as an owner of a vehicle, you should be doing on a regular basis."
A simple check with a 20 cent coin could reveal whether tyres were fit for the road.
"You push [the coin] into the tyre, with the 20 at the bottom, and if you can see the base of the 2 then that means you've only got 2mm of tread and you should consider changing your tyres."
Other things to look out for included "squealing" of the brakes - which meant the brake pads were wearing out - and making sure indicators and lights were working. - APNZ