The government is adjusting the Clean Car Discount scheme, after finding its success was potentially set to put a strain on its self-funded model.

The 'feebate' scheme gives rebates to those buying low-emissions vehicles, and was funded by fees charged to those buying high-emissions vehicles like utes.

More than 100,000 Clean Car Discount rebates had been paid out since its introduction in 2021.

Because of the strong uptake, the scheme was set to reduce 230 percent more emissions than originally estimated by 2025, which Transport Minister Michael Wood said had exceeded industry and government projections.

"The scheme is facilitating an increase in the number of EVs entering the fleet we did not expect until 2027.

"As planned we are further targeting the scheme to maintain its success, and ensure it will be self-funding until its next review," Wood said.

The cap for eligible vehicle's emissions would change from 146g of CO2 per kilometre to 100g from 1 July.

This covered battery electric vehicles and plug-in hybrids, but it meant hybrid-petrol cars would no longer be eligible for the discount.

The rebate paid out on new EVs would reduce from $8625 to $7015, while it would increase from $3450 to $3507 for used imports.

Wood said the increase to used vehicle rebates would encourage more lower and middle income New Zealanders to buy a lower emission car.

The rebate paid out for plug-in hybrids would be reduced.

And a special discount would be introduced for low emission disability vehicles.

Fees charged to buyers of high emissions vehicles would increase, and the threshold for what qualified as a high emissions vehicle would reduce from 192g of CO2 per kilometre to 150g.

"To fund the changes to make it easier for New Zealanders to purchase cleaner imports, we're adjusting charges on high emissions vehicles," Wood said.

"This includes vehicles like utes which are amongst the highest emitting vehicles within our fleet."

The maximum fee imposed would rise from $5175 to $6900 for new vehicles, and from $2875 to $3450 for used imports.

As part of this month's budget, the discount's repayable crown grant would also increase by $100 million.