Seriously, you would be much better off buying a 2 or 3 year old car than participating in this lemon of a program... do the math... you get $4000 toward a new car, and you give up your old car... the dealer will likely inflate the price of that new car by a few thousand anyway, so what you end up with is a new car for $4000 off the sticker price... say the car you want is $20,000, you'd get it for $16,000... if you bought it on contract, with interest it would add up to close to $20000 after 5 years...
buy the same car, used one year, and you'd pay maybe $10, 000, or 8000 or less on a 2 year old car... the cars they make today usually run 15 years or more before their engines start to get unreliable... buy the same car used 5 years, and you'll likely get it for under 3000... same car, 10 years old, can be had for under a thousand, less if the car needs work, but you'd add the cost of the work to the price, bringing it close to the price of the 5 year old car.
so,
pay $16000 plus interest for a car that will last 15 years,
or
pay $8000 for a car that will last 13 years,
or
pay 3000 or less for a car that will last 10 years
brand new car price per year: over $1000 (plus interest)
2 year old car price per year: around $600 (plus interest)
5 year old car price per year: $300
or, even better, keep your clunker, drive it till it dies, price per year $0, then use the money you saved to buy a 5 year old, reliable ride.