Mitsubishi Motors: How did it falsify its fuel economy data?

Tyre Image copyright AFP
Image caption It's all in the pressure

Mitsubishi Motors has admitted rigging data on some of its models' fuel efficiency. About 625,000 cars sold in Japan were affected, and the production of the relevant models has been halted.

The inaccurate tests involved 157,000 of its own cars - the ek Wagon and eK Space - as well as 468,000 vehicles produced for Nissan - the Dayz and Dayz Roox.

What has Mitsubishi done?

Car companies try to outdo each other on how fuel-efficient their models are. It impresses consumers because it's good for the environment, and it's easy on the wallet at the petrol station.

Fuel efficiency is tested by putting cars on what is essentially a treadmill where they run at a certain speed and fuel consumption is measured.

Mitsubishi appears to have overinflated the tyres, which gave better results on the fuel efficiency test.

Imagine inflating your bicycle tyres to the maximum and going up a hill, then letting half the air out and going up the same hill again. It's much harder. The extra muscle you need gives you an idea of the extra fuel that a car would burn through.

Image copyright Bongarts
Image caption That climb is even harder with half the pressure

The controversy comes hard on the heels of the Volkswagen emissions scandal but is slightly different.

Volkswagen installed hidden software in its diesel models that detected when an official emissions test was being conducted. The software would then lower the emission so the test readings were more favourable.

So VW rigged the level of harmful gases coming from the exhaust pipe to make their cars look greener than they were.

Mitsubishi rigged the fuel consumption readings so their cars would appear to use less fuel than they actually did.

Mitsubishi: Cars, aircon, fridges and nuclear?

Mitsubishi is a somewhat confusing brand. There are a whole host of independent companies that share the name and trace their origins back to the original Mitsubishi company founded in 1870 in the shipping industry.

The current companies though are entirely independent from each other.

That means you will find the name in aviation, banking, air conditioners, the nuclear and chemical industry, optics and of course, cars.

Image copyright AFP
Image caption The eK Wagon is one of the models affected

Mitsubishi Motors is the sixth biggest car maker in Japan and number 16 worldwide.

Large-scale production got under way in the 1960s. In 1977 the company entered the European market and in 1982 the US market. Annual car production currently stands at 1,218,853 vehicles.

The current scandal is at Mitsubishi Motors. Any damage to the brand name though, might spill over to the other companies.

Has Mitsubishi been involved in any other scandals in the past?

It's not the first time that Mitsubishi Motors has been in the headlines for misconduct.

In the early 2000s, the company had to admit to lying about defects in its cars for decades.

Back then, an internal investigation found that the firm had covered up faults since 1977 and repaired cars secretly, instead of reporting the problems to the transport ministry.

The cover-up led to huge recalls, criminal charges against several employees and a cost of billions to the company.

More on this story