Germany’s largest automaker said Thursday it is investigating the performance of its latest generation of diesel engine, the EA288, after having previously insisted that there were no problems with it.

The news follows a slow drip of circumstantial evidence suggesting that its doctoring of emissions data involved more people and more cars than previously admitted. If substantiated, that could lead to VW facing far larger fines and criminal penalties than reckoned with so far. VW’s head of operations in the U.S., Michael Horn, had told a Congressional committee earlier this month that the rigging had been done by a small circle of senior engineers.

Suspicions of problems with other engines rose after Horn said VW would withdraw its application for regulatory certification for its 2016 diesels in the U.S. because of the software it contained.

At the weekend, Reuters had reported that VW had made several versions of the ‘defeat device’ software installed in the EA189 engine. The EA288 started to replace the EA189 from 2012, and runs many of VW’s biggest-selling vehicles, including its VW-brand Golf.

In a statement Thursday, said that “no software is embedded in vehicles with the EA288 that would constitute an illegal defeat device, according to legislation.”

It also repeated its assurances that vehicles now on sale under the so-called Euro 6 standard conform to E.U. regulations (albeit those regulations mean little because they aren’t based on hard testing under real-world driving conditions). The engines have already received the blessing from Germany’s auto watchdog, the KBA.

However, it admitted that “the levels of emissions from the EA288 are currently being investigated further.”

No-one was immediately available to explain that cryptic sentence.

Volkswagen will have to recall some 8 million cars with the EA189 engine across the E.U., and another 482,000 in the U.S.. The recall action isn’t likely to finished till the end of next year at the earliest.