TheUngeek: Dealers cannot for any reason contract out of the cga. Even via trademe auctions. Lots get caught out by that. Dealers sells via auction, all cga still applies.
First thing you have to do is contact the dealer. You mist give then a chance to repair first. Failing that call the MTA for advice. You will find depending on the age and milage the dealer will help out.
Rear the MTA mag, lots of examples of dealers sorting out cars many months after purchase as they have failures not considered reasonable for the age.
This ^^^ is incorrect.
See the actual law here.

When a dealer gets an old beat up tradein they sell as dollar reserve on trademe solely because then its NOT covered by any come backs and fair enough too.
Its hard enough trying to make a living out of used cars these days and all the possible comebacks already that are possible way after youve sold a good car.
All sorts of things can happen to a car and who do the public blame and come running to fix it? the poor old car dealer.
Theres next to no margin in used cars these days, its not like the 90's where dealers where able to make a chunk of change. These days you have to sell hundreds of cars a year to make a decent salary for one person!
If you have salesman to pay and yard lease, power bill, petrol for an entire yards worth of cars and test drives, commercial insurance (3 times more expensive than personal) to cover all the stock, finance interest payments...it goes on and on.
Still Joe Public wants the car for next to nothing and will come back and want the dealer to pay a workshop to diagnose and repair any number of faults on a 8 year old car a year after they bought it!