But cash-strapped borrowers aren’t the only destabilizing factor. As big banks like ­JPMorgan Chase and Wells Fargo have stepped back from the sector, nonbank lenders that specialize in auto finance have filled the void. Many of them are “not regulated as prudently as banks are,” according to Mayra Rodríguez Valladares, managing principal at financial consultancy MRV Associates, and “have been loosening their underwriting standards.”