VW in particular is still struggling to come to terms with the so-called “dieselgate” scandal which erupted in late 2015 after it admitted to fitting millions of diesel engines worldwide with software to distort data on the amount of poisonous gases they were emitting.
But Der Spiegel said that the KBA vehicle licensing authority is now set to recall some Mercedes-Benz Vito vans produced by Daimler, as well.
The suspicions this time concern a software device that regulates the amount of a special fluid known as AdBlue used in the engines to neutralize harmful nitrogen oxides (NOx).
Nitrogen oxides are poisonous, can contribute to acid rain and suffocating smog and can cause breathing problems and headaches in humans.
“We are in a technical exchange with the KBA,” about the vans, a Daimler spokesman told AFP, saying around 1,000 of the 1.6-litre models were affected in Germany.
Quoting transport ministry sources, Der Spiegel reported that officials in Berlin believe the software amounts to an “illegal defeat device”, designed to cheat regulators' emissions tests.
“What's more, it is believed that this kind of manipulation could be found elsewhere” in Daimler's range, the weekly added.
But Daimler denied any wrongdoing.
“We would take all legal means against the allegation of a defeat device,” the Daimler spokesman said, while adding the firm would “continue to cooperate fully with the authorities”.
VW also remains in officials' sights.
KBA investigators have discovered “questionable” software functions in Macan SUVs produced by VW's subsidiary Porsche and could rescind the luxury cars' licenses, Der Spiegel reported.
If the licenses are withdrawn, VW might have to buy thousands of vehicles
back from their owners.
VW's own-brand van range has also raised questions, with officials suspecting its popular T6 Transporter consumes more fuel and emits more carbon dioxide than the company claims in its advertising.
The group denies offering misleading statistics for the Transporter.
The new reports come as the German auto industry faces a decisive week, with the Federal Administrative Court set to decide whether diesel vehicles can be banned from parts of major city centres like Düsseldorf or Stuttgart to slash pollution.