Volkswagen emissions scandal: car manufacturer issued recall in April to appease suspicious regulators

US drivers were asked to go to a dealer for a software update

Volkswagen's US arm wrote to car owners in the US state telling them of an "emissions service action" needed on their vehicles (Reuters)

Regulators' growing suspicions about the accuracy of the vehicles' emissions tests prompted Volkswagen to issue a recall of its diesel powered cars in April, four months before the emissions scandal that culminated in the firing of the Volkswagen CEO on Wednesday.

Volkswagen's US arm wrote to car owners in the US state telling them of an “emissions service action” needed on their vehicles, Reuters said.

They were asked to go to a dealer for a software update to ensure exhausts were “optimised and operating efficiently”.

What Volkswagen did not say was that the action was a response to concerns from regulators who were beginning to question the results of emissions tests on Volkswagen's diesel cars, the news agency added.

The revelations follow days of crisis at the car-maker after it admitted it had in fact cheated on US emissions tests.

The ruse involved installing “defeat devices” in vehicles that masked the true level of emissions while in a testing environment.

The US Environmental Protection Agency found that the affected VW and Audi cars emit 10 times to 40 times the legal limit of harmful nitrogen emissions during normal driving.

The company now faces multiple probes, including a criminal investigation by the US Department of Justice, as well as possible class action law suits.

VW boss Martin Winterkorn yesterday fell on his sword after coming under intense pressure from the company's board, shareholders and even German chancellor Angela Merkel.

Winterkorn said he would leave to give the company “a fresh start” after the scandal.

Reuters said US officials had agreed in December last year to allow a voluntary recall of Volkswagne's diesel cars to fix what the company described as a technical glitch.

The letters sent in April were part of that recall.

“This is one of the fixes they presented to us as a potential solution. It didn’t work,” California Air Resources Board spokesman Dave Clegern told Reuters.