German Report Finds Large Gap Between Lab Results and Real-world NOx Emissions in Diesel Engines

After testing 53 models of passenger vehicles meeting Euro 5 and 6 emissions requirements for diesel engines, the German federal motor transport authority (Kraftfahrt-Bundesamt) found that laboratory testing and real-world testing yield significantly differing results in emissions. The report has resultedin 630,000 vehicles being voluntarily recalled by manufacturers to change emissions controls.

Specifically, the report found that diesel engines utilizing a thermofenster (thermal window) technique to limit emissions controls during engine operations at low temperatures, legally allowed as a means of protecting the engines, may be too aggressive. This results in the engines bypassing the emissions controls too often, resulting in higher emissions – especially of NOx gasses. The German transport minister has asked for a further restriction of that thermal window and most manufacturers are complying voluntarily, issuing the recall to change systems on affected vehicles.

Aaron Turpen
An automotive enthusiast for most of his adult life, Aaron has worked in and around the industry in many ways. He is an accredited member of the Rocky Mountain Automotive Press (RMAP), the Midwest Automotive Media Association (MAMA), the Texas Auto Writers Association (TAWA), and freelances as a writer and journalist around the Web and in print. You can find his portfolio at