If I cosigned for an auto loan and the person I signed for passed away, am I responsible for the loan if I turn the car in?

If you surrender the car to the lender, the lender will sell the car and apply the proceeds of the sale to the loan balance. If the proceeds are not enough to pay off the loan in full, you will remain liable for that deficiency balance. If you file bankruptcy, you will be relieved of that liability.

Yes. They will sell the car at a low price at an auto auction and hold you liable for any deficiency (difference between the sales price and the debt.) If you have title to the car (e.g., it was held in joint tenancy with right of survivorship), check the value in one of the standard price guides, take it to a dealer and offer to sell it. Get a quote in writing. Send the quote to the finance company and ask them to release the title for payment in that amount. You are still liable for any deficiency, but you are likely to get more than it would bring at an auction. If the finance company refuses to release the title, they may have violated the law and either barred themselves from recovering a deficiency, given you a claim for statutory damages, or both.