NEW YORK — Suzuki Motor said Wednesday that it had used improper methods to determine the fuel economy of 16 vehicles it sells in Japan, adding to the list of automakers under scrutiny for how they perform in government tests.

Suzuki said that it had not sought to mislead customers, and that its testing had not exaggerated mileage ratings. It said it did not plan to restate any published ratings.

Still, the disclosure is likely to add to industrywide doubts over carmakers and the fuel-test results they report to governments around the world.

That scrutiny has hit Japan’s auto industry in recent weeks. On Wednesday, Mitsubishi Motors said that Tetsuro Aikawa, its president, would resign after the company’s disclosure that its engineers deliberately used unapproved test procedures that exaggerated fuel performance by as much as 15 percent on some models.


Mitsubishi’s new partner and financial savior, Nissan Motor, was accused by South Korean environmental regulators this week of cheating on fuel tests. Nissan has disputed the accusation and said it was working with regulators in that country.

Suzuki shares fell more than 9 percent in Tokyo on Wednesday.

Osamu Suzuki, Suzuki’s chairman and chief executive, apologized to customers but said the company had retested its vehicles and found no significant differences between the results and their already-published ratings.

The problem centered on the same testing regulations that tripped up Mitsubishi: the way engineers calculate what is known as running resistance, or the effect that tire friction and other factors have on fuel consumption under various driving conditions.

Suzuki said mileage tests at Suzuki’s development track in central Japan had produced inconsistent results, which engineers attributed to wind. The track is on high ground near the sea.

Instead of running multiple tests to produce an average, Suzuki engineers cut corners by extrapolating running resistance from past tests, the company said. That was a violation of regulations, the company said, but did not distort results “beyond the standard margin of error.”