More than 250,000 rigged Volkswagen diesels are still on the streets after the pollution scandal broke in 2015, the Star can reveal.
The company says it has fixed 833,272 of the 1.1 million affected vehicles in the UK - including 20,000 in Sheffield.
That leaves 266,728 still pumping out up to 40 times what is allowed in the US.
Worldwide, the company has admitted selling 11 million rigged diesels producing more noxious gas than tests would suggest.
Road charity Brake says air pollution causes the premature deaths of an estimated 700 people in South Yorkshire each year.
Sheffield has been missing EU nitrogen dioxide targets since 2010 and the council says it is ‘not likely’ to be below the legal limit until at least 2020.
A VW spokesman said: “The campaign is a voluntary service action rather than a safety recall. It will remain open for the foreseeable.”