Audi has halted deliveries of seventh generation A6 and A7 models fitted with its V6 diesel engine after discovering “irregularities” in the unit’s management software.

The issue relates to the 268bhp V6 variant of the Gen2 evo engine that's used in the outgoing A6 and A7. The German transport ministry has now summoned Audi for a formal hearing about whether the units were fitted with a ‘defeat device’ to help the cars pass emissions tests.

In a statement, Audi said it discovered irregularities during “internal investigations of the diesel issue”, adding that it immediately reported the discovery to the Kraftfahrt-Bundesamt (KBA), Germany’s Federal Motor Transport Authority, as well as the Luxembourg vehicle registration authority.

Audi CEO Rupert Stadler said: “We regularly inform the KBA about the results of our systematic engine test programme. We report any abnormalities to the licensing authority since our highest interest is in full disclosure. We did that immediately in this case.”

The issue was first reported by German magazine Der Spiegel, which claims that around 30,000 vehicles in Germany are affected. A total of 60,000 vehicles around the world are understood to have the affected engines fitted.

According to a statement obtained by Reuters, the KBA has requested a hearing with Audi due to the suspicion that the cars “have been fitted with an illegal defeat device”. 

Amid the Volkswagen Group's Dieselgate scandal, Audi was previously quizzed over whether emissions-cheating software was fitted to diesel A6 and A7 models sold between 2009 and 2013.