The second-to-last obstacle to to continuing the Cash For Clunkers program, i.e. securing another $2 billion, has been removed with the Democrats successfully stopping the Republicans from adding any amendments to a vote of 65-32.
Essentially, the Republicans attempted to stop the program by adding any sort of amendment they could to the bill, including some ones Dems would normally vote for like a larger tax credit for first time home owners. This was done because, were the Senate to attach even one amendment, the bill would have to go to conference committee and then back to the House to be voted on, which isn't likely to happen while the U.S. House is in recess.
The final obstacle is passage in the Senate, but at this point it's a foregone conclusion since all the amendments were defeated. Unless the President decides to suddenly oppose the bill (unlikely), there will be another $2 billion in the pipelines.