VW chief Martin Winterkorn is having a crunch meeting with members of the firm's board over the "defeat devices" used to fool emissions tests on diesel cars.
Volkswagen admits the software – which kicks in during exhaust tests – may be in some 11 million vehicles worldwide.
The "defeat devices" meant true emission levels, as much as 40 times the level legally allowed in the US, were hidden.
At least 482,000 cars are to be recalled & the world's largest car maker could face penalties of more than $18bn in the US alone.
It moreover faces a criminal investigation in the US & further probes in countries including Germany, France & South Korea.
Angela Merkel, Germany's Chancellor, has urged the firm to act "as quickly as possible" amid fears the scandal could affect the country's economy.
Volkswagen's boss has apologised yet offered no undertaking to resign following eight years in charge that have seen VW almost triple it profits.
It is not clear if Mr Winterkorn was aware of the emissions-rigging software.
"I am endlessly sorry that we have disappointed this trust," he said in a video message on Tuesday.
"I apologise in every way to our customers, to authorities & the whole public for the wrongdoing. We are asking, I am asking for your trust on our way forward. We will clear this up."
A US law firm said on Wednesday it was suing Volkswagen in a class action lawsuit.
Chicago lawyer Robert Clifford said the impact was "massive" & that car buyers had not received what they paid for.
He said people were moreover affected because their car could now be worth less.
Mr Clifford claimed VW owners could have problems keeping their car on the road as officials might refuse to issue relevant permits.
New York Attorney General EricÂ Schneiderman has moreover confirmed an investigation.
"No company should be allowed to evade our environmental laws or promise consumers a fake bill of goods," said MrÂ Schneiderman
Volkswagen has set aside â‚¬6.5bn (Â£4.6bn) to cover the scandal & has warned the bill could rise.
There are fears cars in the UK could moreover be recalled Â and that investigators might find similar devices were used by other firms – including in petrol cars.
Source: “Sky News”