Auto sales have yet to fully recover from the economic downturn and dealers say they are facing a stubborn obstacle: Your used car is working just fine.

For years the auto industry has counted on car owners wearing out or tiring of their current rides and buying new. But owners are holding onto their cars much longer now, in part because cars last longer than they used to. Not only is this stunting sales of new cars, but also depriving dealers of an important source of secondary income — used cars they received as trade-ins.