Suzuki Motor Corp. submitted weather data as part of fuel efficiency test results possibly to cover up the fact that it used data from indoor tests rather than road tests as required by the government, sources close to the matter said.

Suzuki recently admitted it collected data needed for determining vehicles' fuel efficiency from wind tunnel testing.

Under Japanese regulations, automakers are required to use a road testing method known as a "coasting test" to gather data on rolling and air resistance.

Suzuki said it used the coasting test method on all models but said it could not use the data gathered because it was significantly influenced by weather conditions, such as wind.

The company denies trying to pad the fuel efficiency numbers of its vehicles and says there is no need to correct numbers for any of the affected models.

The transport ministry has ordered the automaker to file a further report by May 31 on its testing methodology before deciding how to respond in the case.

News of Suzuki's noncompliant fuel efficiency testing surfaced shortly after Mitsubishi Motors Corp. admitted to cheating on fuel efficiency testing for several models, using running resistance data from desktop calculations.