From CBS:

The Obama administration is developing plans to wind down the popular Cash for Clunkers program and could announce by Friday when the incentives will no longer be available.
Transportation Secretary Ray LaHood said Wednesday the department would announce within 48 hours how it intends to discontinue the program that offers car buyers rebates of $3,500 or $4,500 for trading in older vehicles for new, more fuel-efficient models. Department officials met with car dealer trade groups on Wednesday to discuss how the program will eventually end and respond to complaints over a backlog of rebate payments to dealers.