i have joint account on auto finance can bankruptc

If the co-owner is not filing bankruptcy jointly with you, then the bankruptcy filing won't hurt him/her. However, if you file Chapter 7 bankruptcy, you may get a discharge from paying the debt but the co-owner will become solely responsible for paying it. If you file Chapter 13, you will get a payment plan in order to pay off the debt.

Being that a auto finance is usually a secured loan, chapter 7 would discharge the debt and the vehicle would be surrendered. This more than likely would affect the coborrower as it would state "included in bankrutpcy"...even though they did not file, the tradeline would appear. The cosignor is just as legally liable for the debt as you.