Nissan said today it had unearthed misconduct related to exhaust emissions and fuel economy measurements for 19 models sold in Japan.

This marks the second case in under a year where misconduct has been discovered in its inspection processes. 

Japan's second-largest car maker said it had found that the testing environments for emissions and fuel economy in final vehicle inspections at most of its factories in Japan were not in line with requirements.

It also discovered that inspection reports were based on altered measurements. 

"A full and comprehensive investigation of the facts including the causes and background of the misconduct, is underway," Nissan said in a statement.

It added that the issue was discovered during voluntary compliance checks it launched following last year's improper vehicle inspection scandal. 

Nissan said the misconduct did not compromise the safety of the affected models, and that mileage readings were in line with levels presented in product catalogues.

It was in the process of compiling data for the low-production GT-R sports car to confirm that it satisfies safety standards. 

In October last year, Nissan said that for decades uncertified inspectors had signed off on final checks for cars sold in the country, triggering a domestic recall of 1.2 million vehicles. 

The company blamed staffing shortages for the misconduct, which contributed to a slide in full-year operating profit in the year ended March.

Nissan said today it would take appropriate action to prevent future occurrence.