Regardless of the type of property involved, the Buyer is the legal property owner, until he misses enough payments, to be in violation of his financial agreemnt, thus allowing the Financier to take legal possession of the property. Even then, dependent on the typeof property, the orignal legal owner may still have Rights to the property, the Financier may not be able to dispose of the property and recoup his investment, until yet another time period has pass, that would allow the original Owner to fulfill the financial Contract.
Homes comes to mind. In Iowa, one can repossess but cannot sell , for one year, during which the Orignal Owner h as an opportunity to repay the laon, with fees, and retain possession of his home. Some folks buy those home sup, as an investment and do not care either way. Get paid for the loan and fees or repossess and sell it for a profit.
Either way, money is made at a nice rate of return.
Getting to what GM is attempting.
Highly doubt it is legal. GM is simply the manufacturer. Once the vehicle is actually sold, they no longer have an interest, of any kind. The warranty is one the vehicle and there are federal mandates involved. VOiding the warranty for perceived, after teh sale, violations is akin to taking ones ball home, except it is no longer ones ball.