Subaru has admitted inspectors at its manufacturing plants in Japan “inappropriately altered” the emissions and fuel efficiency data of some 900 vehicles so that the average data values would pass quality control standards.

An internal investigation demanded by a Japanese government ministry found factory-floor inspectors at the company’s Gunma and Yajima assembly facilities fudged the data on hundreds of cars between December 2012 and November 2017, Autoblog quotes the automaker, and possibly even for a decade before that.

Close to 7,000 vehicles went through final inspections in that five-year span, and Subaru found that its quality control inspectors and their foremen altered the emissions and fuel consumption data on some 903 cars’ inspections in that time, making some vehicles’ numbers better and some worse just to reduce the variation and steer closer to the required standards.

While Subaru does allow some data alterations to adjust for errors made by the measurement equipment, the changes these inspectors made were done via inappropriate methods.

Subaru will not recall any vehicles because it says customers shouldn’t suffer quality issues as a result of the test-cheating and because its quality control standards are already stricter than required by law. Instead it has apologized and says it will ensure such tampering doesn’t happen again.