Japanese automaker Nissan says it found emissions and fuel economy data had been falsified at most of its factories in Japan.
Nissan said data had been deliberately "altered" although the company did not say how many cars had been affected.
The company, which makes the Leaf electric vehicle, uncovered the issues during voluntary testing after its inspection process was deemed faulty by the government.
In a statement, Nissan said it found "exhaust emissions and fuel economy tests that deviated from the prescribed testing environment" and inspection reports were created "based on altered measurement values."
Nissan said the erroneous testing does not affect exports. It also said emission and fuel economy results were still within required limits on all vehicles.
Last September, Nissan admitted unqualified workers had been carrying out final inspections at the end of production lines. The company said those illegal inspections may have dated back to 1979 at its plant in Tochigi.
Nissan is not the first manufacturer to admit falsifying emissions tests. VW admitted using illegal software to cheat US emissions tests on diesel engines in September 2015.
It later admitted so-called defeat devices were fitted to more than 11 million of the group's cars worldwide, including 1.2 million in the UK.
The fallout has cost VW more than $30bn (roughly £22.5bn) to date - the bulk of that sum in the US where, in May, prosecutors filed criminal charges against former VW boss Martin Winterkorn.
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