If a co-signer has taken possession of a vehicle because the borrower became delinquent is the co-signer now responsible for all payments on the car?

If the primary borrower has defaulted on the vehicle loan, the co-signer will need to make regularly scheduled payments and any that have been missed. If the co-signer is unable to do this, the vehicle may be repossessed by the lender. In which case both the primary borrower and co-signer will be responsible for any deficiency and fees incurred when the vehicle is sold. The repossession will also appear on both person's credit report. It would be advisable to contact the lender to discover what options might be available pertaining to the specific circumstances.