German Transport Minister Andreas Scheuer summoned Zetsche after the KBA's discovery, even as Daimler disputes they were illegal.
The auto industry's diesel emissions scandal continues to spread its noxious tentacles.
Daimler declined to comment on the 1 million vehicles figure, but said it is cooperating fully and transparently with the KBA and Germany's Transport Ministry.
Germany ordered Monday the recall of some 774,000 vehicles from Mercedes-Benz maker Daimler across Europe, citing illegal "defeat devices" created to hide high levels of harmful emissions from regulators´ tests.
The Stuttgart-based carmaker has said the US Department of Justice has inquired about the company's emission certification processes, and that German prosecutors in Stuttgart are investigating Daimler employees on suspicion of fraud and criminal advertising.
German newspaper Bild Am Sonntag reported that the Federal Motor Transport Ministry believes the majority of Mercedes' Euro 6 diesel engines are fitted with such devices, which could affect as many as 1million vehicles globally. Last year, Mercedes-Benz retrofitted roughly 3 million cars with modified emissions controls to bring those cars into compliance with Euro 5 and Euro 6 regulations.
Mercedes-Benz C-Class and Vito models with diesel engines and a sports utility variant of the sedan, known as the GLC, were the main cars found to be at fault, the ministry said.
Recent weeks have seen Germany´s KBA vehicle licensing authority hit Volkswagen subsidiaries Audi and Porsche with mass recall orders over their engine control software, as well as a smaller batch of cars from rival BMW.
Daimler hasn't denied the existence of the functions, but have refuted the suggestion that they are illegal.
Daimler Chief Executive Dieter Zetsche said on Monday that the carmaker had found a technical solution for updating the software on its vehicles, and he therefore expected the company to avoid a fine.
'For the existence of the relevant test cycle NEDC, the specific programming in question is not required'.
'Overall, this outcome should de-risk the stock'.