A report by the land ministry showed Thursday that four diesel models of three domestic carmakers emitted two to 10 times more nitrogen oxide ( NOx) when they were running on roads than is allowed by the country’s emissions standards.
The report is based on tests conducted on diesel sedans and cargo vehicles driving on streets and highways. The test followed last year’s global scandal by Volkswagen over cheating on emissions tests.
The report shows that the amount of emissions increased when the vehicles ran on pavement. But their emissions when checked in a test structure where the vehicles’ wheels spun in place met the standards.
Based on the finding, the ministry plans to create new standards for diesel cars driving on roads. At the same time, this could raise concerns among carmakers over the image of diesel cars and the potential higher development costs to keep emissions legal. The ministry also started to consider introducing a test on driving diesel trucks.
The inspection was made on one cargo and five sedan models by Toyota Motor Corp., Nissan Motor Co., Mazda Motor Corp and Mitsubishi Motors Corp. The vehicles were equipped with emissions gauges and driven in towns and rural highways in Tokyo and Saitama Prefecture.
The land ministry noted nitrogen oxide emissions increased when the roads were crowded or when drivers suddenly accelerated.
In Volkswagen’s case, its diesel vehicles were found to be equipped with so-called defeat device software that turned on their pollution controls only during standing emissions tests. There was no such software found on the models the land ministry tested.
The government has offered tax incentives for diesel cars, as it has promoted them due to their high fuel efficiency and lower emissions. In 2015, new sales of diesel sedans in Japan stood 103,804 units.