In April of 2015, Volkswagen of America, Inc.(VOWG_p.DE) sent letters to California owners of diesel-powered Audis and Volkswagens informing them of an “emissions service action” affecting the vehicles. The company didn’t explain that it was taking the action in hopes of satisfying government regulators, who were growing increasingly skeptical about the reason for discrepancies between laboratory emissions test results and real world pollution from Volkswagen’s diesel cars.