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Mitsubishi models in the US are now under the spotlight as the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) are investigating whether models in the country meet fuel-economy regulations, Automotive News reports.

The company has been instructed by the EPA to supply the regulatory body with additional information of its US models. The Japanese automaker has also been ordered to conduct additional testing, according to EPA spokesperson, Julia Valentine.

Called a “coast-down test,” it will be coordinated by the agency and the California Air Resources Board. During the test, vehicles are required to coast to a halt from 128 km/h. With this, readings of aerodynamic drag and friction in the drivetrain will be obtained, along with other information.

Mitsubishi L200 instrument panel-01

Following this, the data will then be programmed into dynamometers, which will allow for simulation of a vehicle’s behaviour on actual roads during lab tests. The automaker admitted that it had deviated from official coasting test procedures since 1991.

The coast-down test has lead to Ford, Mercedes-Benz, Hyundai and Kia amending fuel economy ratings on a number of models since 2012. In 2014, Hyundai and Kia came to a USD$350 million (RM1.3 billion) settlement with the EPA over inflated fuel economy ratings and inaccurate coast down test data. The EPA has since updated its procedures in 2015 as a response to the errors.

In its admission, the automaker stated that driving resistance data measured via the improper tests resulted in a “fuel-economy grade” variant of the 2014 eK Wagon, which was offered in Japan. Under the Nissan brand, the model is sold as the Dayz model.

Meanwhile, the driving resistance data was then later applied to three other variants of the eK Wagon and Dayz model (four-wheel drive and turbo models), rather than data obtained from tests of other versions. The improper calculations (from the eK Wagon) were used on two other models, Mitsubishi stated.

Mitsubishi disclosed that it remains uncertain as to how many vehicles have been subjected to the improper test methods. It has stated that it will be looking into other models apart from the four kei cars and provide a separate report once findings have been obtained.

In Japan, Reuters reports that Mitsubishi Motors chairman and CEO Osamu Masuko along with president and COO Tetsuro Aikawa will likely be resigning over the scandal, which has reduced the company’s market value in half, within a week. Both are expected to step down after the newly set-up independent committee reports the results of the investigation.