The Carbon Emissions-Based Vehicle Scheme(CEVS) was launched to encourage the adoption of cars that are more eco-friendly. The amount of rebate depends on your car's carbon emission.
The rebate comes in the form of an ARF rebate, and therefore, reduces your PARF rebate. Do note that no matter how much the rebate is, you will need to have a minimum ARF payable of $5,000.
You can find the CEVS rebate table here: https://www.lta.gov.sg/apps/news/page.aspx?c=2&id=8aa03b88-409f-4852-b2df-09077e101468