The normal duration of regulatory tests for vehicle emissions is about 20 minutes, the paper added. The Volkswagen emissions-test cheating scandal cast a spotlight on industry-wide emissions of health-threatening nitrogen oxide (NOx) levels in diesel fumes. Following the KBA investigation, the firm and some other top German manufacturers -- Porsche, Opel, Audi and Mercedes -- agreed to recall 630,000 vehicles to tweak diesel engine software technology. While no German manufacturer other than VW was found to have used illegal cheating software, carmakers were making liberal use of something they call a "thermal window" which refers to the time when carmakers are allowed to throttle back emissions management systems in order to protect the engine from condensation or other damage. Auto supplier Bosch [ROBG.UL] is said to have informed German investigators that Fiat was using a mechanism that virtually disabled exhaust filters, Bild am Sonntag reported. Bosch declined to comment.