In 2015, Audi admitted that at least 2.1 million Audi cars had been involved in the Volkswagen emissions testing scandal in which software installed in the cars manipulated emissions data to fool regulators and allow the cars to pollute at higher than government-mandated levels. The A1, A3, A4, A5, A6, TT, Q3 and Q5 models were implicated in the scandal. Audi promised to quickly find a technical solution and upgrade the cars so they can function within emissions regulations. Ulrich Hackenberg, the head of research and development at Audi, was suspended in relation to the scandal. Despite widespread media coverage about the scandal through the month of September, Audi reported that U.S. sales for the month had increased by 16.2%. Audi's parent company Volkswagen announced on 18 June 2018 that Audi chief executive Rupert Stadler had been arrested.