Volkwagen faces billions in fines and its executives risk criminal charges after admitting that it cheated so as to make about half-a-million diesel cars look cleaner-burning than they are.

VW admitted systematically cheating on US air pollution tests for years, the Environmental Protection Agency said on Friday in citing violations that could total $18bn in fines.

Volkswagen admitted it sold 2009-15 diesel Volkswagen and Audi cars with software that turns on full pollution controls only when the car is undergoing official emissions testing, the Environmental Protection Agency said and called the algorithm a “defeat device”.

The agency could fine the company $37,500 per violation, said Cynthia Giles, the agency’s assistant administrator for enforcement. With 482,000 cars part of the case, the total number could reach $18bn.

Also, VW could face criminal exposure according to lawyers, since the Clean Air Act has criminal provisions in cases of tampering with monitor devices, and making false statements.