This is my understanding of cosigning on a loan. Since both names are on the loan, you both have a right to access the car (neither of you own the car, the bank does). Legally it doesn't matter whose bank account the money comes from. If the loan isn't paid in full, it will affect both of your credit scores. I'm definitely no lawyer though so I could be wrong. I definitely wouldn't disable the car or take it back without talking to a lawyer first.