Japanese car-maker Subaru is investigating whether it carried out illegal inspections on its own vehicles and if any recalls might be needed.
Spokeswoman Miyuki Yasuda said the company would submit a report to the government as soon as possible.
Japanese media reports on Friday said unauthorised people had inspected vehicles at two Subaru plants in Gunma prefecture, north-west of Tokyo.
The government ordered car-makers to check their inspection procedures after Nissan apologised for allowing unauthorised employees to carry out vehicle checks for years.
Subaru, formerly called Fuji Heavy Industries, is partnered with Toyota, a top shareholder. Toyota and Honda had said they did not have dubious inspections. Toyota said it was checking with Subaru on the reported irregularities.
The transportation ministry said it had not received a report from Subaru.
Nissan is recalling more than a million vehicles in Japan to re-inspect them, and has set up an investigative team that includes a third party to get to the bottom of the scandal and prevent a recurrence.
The wrongdoing, spanning its six plants nationwide and many years, has stunned the public and cast a shadow over the country's prized "monozukuri", or production, reputed for quality, order and meticulousness.
The problem does not affect Nissan vehicles sold outside Japan and is not believed to have affected vehicle safety as they were final-stage checks.
But the scandal raises serious questions about ethics and professionalism at Nissan, which makes the Leaf electric car and Infiniti luxury models, and is allied with Renault of France and Mitsubishi of Japan.
The vehicle industry has been hit by a series of scandals.
Nissan took a controlling stake in Mitsubishi Motors last year after that company was caught inflating fuel economy figures for its minicar models, which are also sold under the Nissan brand.
Japanese supplier Kobe Steel acknowledged recently that it had systematically falsified data on its products, including steel, aluminium, copper and other materials, affecting some 500 companies including major global car-makers, as well as the aircraft, electronics and railway industries.
Volkswagen of Germany acknowledged in 2015 that it had equipped its diesel cars with illegal software that enabled cheating on US emissions tests. Volkswagen has agreed to more than 20 billion US dollars in fines and civil settlements over the scandal.
Air-bag maker Takata filed for bankruptcy protection after some 100 million air-bag inflators were recalled worldwide. The defect has been linked to 19 deaths and dozens of injuries.