The benefits of rehab don't really appear on your credit report until after 9 months, when the defaulted status is removed and new, positive tradelines are added by your new lender. If you must buy the car in 6 months, I think that consolidating and paying on the new loan for 6 months would be the strongest showing that you are taking steps to improve your credit. BUT, if you went with a local lender, like a credit union, showing them that you are in rehab might be just as effective. Also, rehab has the best effect on your credit long term.
That's a tough call. How is your credit overall? Are these your only negative accounts?
