The newly revealed software makes a pollution control catalyst heat up faster, improving performance of the device that separates smog-causing nitrogen oxide into harmless nitrogen and oxygen gases. Volkswagen already faced an ongoing criminal investigation and billions in fines for violating the Clean Air Act for its earlier emissions cheat, as well as a raft of state investigations and class-action lawsuits filed on behalf of customers. If it is determined the new issue is a second defeat device, that would call into question recent assertions by top VW executives that responsibility for the cheating scheme lay with a handful of rogue software developers who wrote the original code installed with the company's diesel engines starting with the 2009 model year.