Germany's transport minister said Sunday that in the wake of the Volkswagen emission cheating scandal, major automakers would have to disclose their engine software to state regulators.

Alexander Dobrindt also announced there would be follow-up tests by the state motor transport authority KBA to double-check the results of exhaust tests ordered by the manufacturers.

The minister said there would be "a comprehensive package of measures" to tighten the approval process, including "disclosure of engine software" to the KBA, confirming a report in the Bild am Sonntag newspaper.

Dobrindt said carmakers would also regularly have to rotate the auditing organisations they task with carrying out emissions tests on their new models, the newspaper reported.

Volkswagen was plunged into its deepest-ever scandal in September, when it was forced to admit it had installed emission cheating software into 11 million diesel engine vehicles worldwide.

VW was found to have used so-called "defeat devices" that activate emissions controls during testing, then turn them off under normal operations, allowing illegal amounts of nitrogen oxide to spew into the air.

The costs facing VW, once seen as the paragon of German industry, are still incalculable, in terms of reputation and global earnings and because it faces billions in possible fines and legal costs.