Germany's transport ministry reportedly said it would order about 100,000 Opel vehicles to be recalled as part of an emissions probe, after prosecutors searched the PSA-owned automaker's offices earlier on Monday (15 October).
According to a Reuters report, citing a ministry statement, German motor vehicle authority KBA found four software programmes capable of altering vehicle emissions in 2015, and ordered Opel to implement a software update in cars to remove them.
"After a fifth software device was discovered in early 2018, which KBA found to be illegal, there is currently an official hearing going on with the goal of imposing a mandatory recall for the Cascada, Insignia and Zafira," the statement said.
Opel told the news agency it was fully cooperating with authorities but that it could not comment on details of the investigation.
"Opel reaffirms that its vehicles comply with the applicable regulations," the automaker added.
The transport ministry said Opel had stalled on the hearing. The KBA had told Frankfurt prosecutors about the software device in April, it added.
"The official recall of the affected roughly 100,000 vehicles will take place shortly," it added.
Reuters noted German prosecutors had searched offices at Opel's sites in Ruesselsheim (near Frankfurt) and Kaiserslautern earlier on Monday.
The Frankfurt prosecutor's office told the news agency it was probing 95,000 vehicles equipped with Euro 6d engines.
PSA Group, which owns both the Opel and Vauxhall brands, declined to comment to Reuters.
The report noted the Insignia, Zafira and Cascada were developed when Opel/Vauxhall was still owned by General Motors which subsequently sold the automaker and the two brands to PSA in 2017.
Reuters also noted Opel had admitted in 2016 the Zafira contained engine software which switched off exhaust emissions treatment systems under certain circumstances but insisted at the time that it was making use of a legal loophole.