It is irrelevant who is the co-signer and who is the primary signer. It affects your credit EXACTLY the same.
It will take a while, but you should see a jump in your score...granted you are paying the payments on time. AND as long as ALL your other payments (i.e. credit cards, cell phone and etc.) are paid on time also.
It will take A LOT longer than a few months, but you should see it improve.
From your friendly Toyota Salesperson