One year ago, Volkswagen's cheating on emissions tests for millions of its diesel cars erupted into public view, leaving the mammoth carmaker battling an unprecedented crisis.

The German company has sought to make amends with mass recalls and a fresh focus on building cleaner cars, but a mountain of legal complaints and ever-louder demands for compensation have made it difficult to turn the corner.

Just on Friday, two legal claims landed on Volkswagen's doorstep with Blackrock -- the world's largest investment manager -- saying it would join a legal action accusing the car giant of misleading shareholders, echoed by the German federal state of Hesse.

The scandal "has had huge effects on Volkswagen and the whole sector", said industry expert Stefan Bratzel of Germany's Center for Automotive Management.

VW built itself over decades into Europe's car champion and now sells vehicles under 12 separate brands -- from Seat, Skoda and Volkswagen to luxury brands Audi and Porsche.

The firm rakes in 200 billion euros ($225 billion) in sales each year and employs 600,000 people globally.

But the Wolfsburg-based group was rocked to its core when US regulators on September 18, 2015, accused it of deliberately skewing emissions data.

VW then publicly admitted it had installed so-called "defeat devices" in 11 million diesel-powered vehicles around the world.

The software is able to detect when cars are undergoing regulatory tests and lowers their emissions accordingly, giving them the appearance of being less polluting than they really are.

In response to the revelations, Martin Winterkorn resigned as chief executive while insisting he had known nothing of the scheme, leaving then-Porsche boss Matthias Mueller to take over the whole group.

- Stock market blues -

So far VW has put aside 18 billion euros in legal provisions, which pushed the company last year into its first annual loss in more than 20 years.

When the crisis broke, investors watched in horror as VW stock lost 40 percent of its value in just two days -- burning up 30 billion euros of market capitalisation.

One year on, VW remains valued around 20 percent lower than it was before last September.

Beyond stock markets, the scandal triggered no collapse in business for the Volkswagen brand, which on Friday reported that sales fell by just 0.2 percent worldwide in January-August 2016 compared with the same period last year.

That period, though, saw 30,000 fewer cars with the circular VW badge drive off the dealers' lots in the United States -- a drop of 13 percent.

- Miles to go -

"One year after 'dieselgate', Volkswagen has maybe gone 50-60 percent of the way, but there's still a lot to do," Ferdinand Dudenhoeffer, director of the Center for Automotive Research at the University of Duisburg-Essen told AFP.

In the United States, the firm was able to reach a deal settling some of the claims, agreeing to pay almost $15 billion in fines and in compensation to some 480,000 car owners.

At home in Germany it faces lawsuits from hundreds of investors claiming at least 4.0 billion euros.

In the suit joined by Blackrock, the plaintiffs accuse VW of failing to disclose the looming scandal to investors in a timely fashion.

And VW still faces other legal claims in the United States as well as lawsuits and probes around the world, including in Australia, South Korea, France and Italy.

Meanwhile, European authorities are stirring in Brussels, animated by the charge that American VW customers are being treated better than EU citizens affected by the scandal.

So far, VW has refused to compensate Europeans or buy back their vehicles. Instead, it plans to retrofit the 8.5 million vehicles concerned to meet emissions standards.

Experts predict the total bill for Volkswagen could reach between 25 and 35 billion euros, leaving the firm once again raiding its piggy bank but not threatening its survival.

- 'Turning point' -

Dudenhoeffer suggests that 'dieselgate' could in the end be a "boon for Volkswagen".

New CEO Mueller has adopted a bold strategy, promising dozens of new electric vehicles in coming years as well as pushing into fields like car-sharing services and self-driving cars.

VW's cheating has also seen regulators step up scrutiny of the whole industry, shining a spotlight on the harmful effects of polluting engines.

The scandal has been a "turning point for diesel", said Bratzel of Germany's Center for Automotive Management.

From September 2017, carmakers will submit vehicles for on-road testing as well as laboratory probes, forcing them to invest in more effective anti-pollution systems.

Five things to know about VW's 'dieselgate' scandal
Frankfurt (AFP) Sept 16, 2016 - It has been a year since Volkswagen admitted to fitting millions of cars with cheating software to dupe emissions tests, plunging the German auto giant into one of the biggest scandals ever to hit the industry.

Billions of dollars in compensation later and mired in legal woes and mass recalls, Volkswagen is still nowhere close to drawing a line under the nightmare.

Here's what you need to know on the first anniversary of 'dieselgate'.

What's it all about?

US authorities on September 18 accused VW of installing so-called "defeat devices" in nearly half a million cars between 2009 and 2015 to make them seem less polluting than they were.

Investigators found that some cars spewed out up to 40 times more harmful nitrogen oxide -- linked to respiratory and cardiovascular diseases -- than legally allowed.

Volkswagen confessed that 11 million diesel vehicles worldwide were fitted with the manipulating software, sending the carmaker's shares into a tailspin.

Most cars affected bear the Volkswagen brand, but vehicles made by other VW group companies such as Audi, Seat and Skoda were also equipped with the software.

VW's chief executive Martin Winterkorn offered his "deepest apologies" to the public but denied any personal wrongdoing. He resigned on September 23.

What are they doing to fix it?

After its admission, Volkswagen announced a global recall of all affected vehicles to fix the emissions manipulation.

It also offered to buy back cars and pay compensation -- but only to owners in the United States, much to the annoyance of EU authorities.

VW took a major step towards resolving the dispute in the US in June, when it agreed to a massive $14.7-billion (13-billion-euro) settlement.

The deal will see the auto giant refit or buy back some 480,000 VW and Audi cars with 2.0-litre diesel engines. Owners of those cars will also receive up to $10,000 each in cash compensation. Some of VW's money will also go towards environmental projects.

The carmaker still needs to resolve a slew of other US complaints, and remains barred from selling diesel vehicles in the country.

How bad is it for Volkswagen?

The financial hangover has been pretty bad, and could get worse.

Aside from ongoing litigation in the United States, VW is facing probes and lawsuits around the world, including in Germany, France and South Korea, setting the stage for more fines and compensation demands.

The company says it has set aside around 18 billion euros to cover repairs, buy-backs and legal costs, but experts believe the final bill will be much, much higher.

Dragged down by such costs, the group reported a 1.6-billion-euro net loss last year, its first in over two decades.

VW is also under growing pressure from the EU to offer compensation to European customers. While the European Commission cannot itself take any action, it last week urged member states to crack down on the company for violating consumer protection laws.

VW says it has no legal obligation to fork out cash for European drivers and insists that doing so could bankrupt the company, a major employer in several EU countries.

Have other carmakers been cheating?

Tests carried out in the wake of the scandal found that diesel engines by other carmakers were also more polluting on the road than during testing. But there is no formal indication any of them installed cheating software.

Rather, the manufacturers in those cases said regulations allowed deactivation of emissions controls in certain conditions to protect the engine.

Still, German makers Audi, Mercedes, Opel, Porsche and Volkswagen decided this year to voluntarily recall around 630,000 cars to fix emissions irregularities.

There's also a spat brewing between Germany and Italy after Berlin accused Fiat-Chrysler of using defeat devices in some vehicles, strongly denied by the firm and Italian authorities.

How have customers reacted?

With remarkable sangfroid. VW group sales have plummeted in the US -- down nearly seven percent this year -- but European drivers appear to have largely shrugged off the controversy.

The VW group maintains the largest share of the European car market, around 25 percent, and Audi and Skoda drove it to higher sales in the first eight months of 2016 than over the same period last year.

In figures released on Friday, the group said global sales of its vehicles increased by 1.8 percent between January and August compared with the same period in 2015.

But the US saw 30,000 fewer own-brand cars marked with the famous circular VW logo drive off dealers' lots -- a fall of 13 percent.