Nissan has admitted that it has uncovered falsified data from car exhaust emissions tests at most of its Japanese factories.
The firm did not disclose how many cars were involved, but said emissions and fuel economy tests had “deviated from the prescribed testing environment”.
The carmaker added that inspection reports had been “based on altered measurement values”.
Nissan pledged there would be a “full and comprehensive investigation”.
It added that “appropriate measures” would be taken to stop any future recurrence.
Nissan’s shares fell more than 4.5 per cent on Monday after the company alerted investors that a statement on exhaust emissions was imminent.
Last year, Nissan recalled 1.2 million vehicles in Japan after regulators said safety checks did not meet domestic requirements.
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.”
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.
A subsequent investigation into why its safety inspections did not meet government standards has now led to the latest revelations.
The admission by Nissan comes after a huge scandal involving diesel emissions test cheating by Germany’s Volkswagen.
Last month, VW was fined €1bn (£880m) by German prosecutors for selling more than 10 million cars between mid-2007 and 2015 that had test-cheating software installed.