Possible irregularities with the company's fuel economy numbers were raised during the compilation of a report into uncertified trainees, who were involved in the final inspection of its domestic market vehicles.
Some inspectors interviewed by investigators reportedly said fuel consumption tests could have been doctored during the inspection process.
Subaru released the conclusions from the report yesterday, but made no mention at the time about concerns regarding its fuel economy figures.
"At the moment we are trying to confirm whether data was indeed fabricated, and if so, how this happened and which models are affected," Miyuki Yasuda, a Subaru spokeswoman, told Reuters.
She noted, should any discrepancies be found, a recall was unlikely as incorrect fuel economy numbers would not be a breach of safety regulations.
The company is also said to be investigating if exported vehicles are affected.
Should there prove to be any impropriety on Subaru's behalf, it will be the latest in a string of scandals tarnishing the image of Japan's industrial sector.
More recently, both Nissan and Subaru have admitted to using unqualified personnel to perform final inspections on its domestic vehicles. In October, Kobe Steel confessed to falsifying inspection certificates for the metal products it shipped to clients.